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FAQ

Last Update: 03/23/2008

 

GENERAL ZR-1 INFORMATION

 

QUESTION: What is a ZR-1 Corvette and how do I recognize one?
QUESTION: What is different about the ZR-1 engine?
QUESTION: I heard the LT5 engine in the ZR-1 wasn't design by GM?
QUESTION: How many ZR-1's did GM build?
QUESTION: I understand there was a horsepower change at some point?
QUESTION: Are all ZR-1's the same?
QUESTION: When was the last ZR-1 built?
QUESTION: Why did GM stop building ZR-1's?
QUESTION: How fast are ZR-1's?
QUESTION: Can any Chevy dealer work on a ZR-1?
QUESTION: How much was the ZR-1 option?
QUESTION: Could you buy a ZR-1 convertible?
QUESTION: Could you buy an automatic ZR-1?
QUESTION: I heard that the LT5 wasn't built by GM?
QUESTION: What is that little cut out I see in the bottom of the windshield?
QUESTION: How do you recognize a ZR-1?
QUESTION: Which thermostat is in the ZR-1, 180 or 195 degree?
QUESTION: I bought a '90 or '91 and I didn't get an owners kit? What is in this owners kit?
QUESTION: Are there any options that are rare on a ZR-1?
QUESTION: How many 1990 ZR1s were shipped with manual AC (C60)?
QUESTION: I understand there is a build sheet somewhere on the ZR-1?
QUESTION: How can I get a copy on my window sticker? 
QUESTION: What is that keyhole below the radio for? 
QUESTION: I want to buy a ZR-1 but I heard so many stories about cost of parts and other issues?
QUESTION: What's in the '93-'95 owners kit?
QUESTION: Are the 6-speed transmissions in the ZR-1 the same as in other 6-speed C4s?
QUESTION: Are the roof panels stamped with a VIN number?
QUESTION: What is this ZR-1 "Black Motor" I hear about?
QUESTION: I understand a second design head was introduced in late production engines?
QUESTION: How come you can't buy just the cam covers without the heads?
QUESTION: Are the "power keys" special or coded for each ZR-1?
QUESTION: What about oil break in for '90-'92 ZR-1s vs '93-'95 ZR-1s?
QUESTION: What's the story with Birmel vs Dunn heads on the later model ZR-1's?
QUESTION: Are there any durability differences between the 2 bolt '90 - '92 LT5 engines and the 4 bolt '93 - '95 LT5 engines?
QUESTION: What are the changes between each year?
QUESTION: I understand there are some differences in transmission gears and torque in late MY ZR-1's?
QUESTION: Is the AC compressor in the ZR-1 the same as in other C4's?
QUESTION: What is the weight of the LT5 engine?

QUESTION: What is this ZR-1 "Black Motor I hear about?

QUESTION: I heard the first year for the ZR-1 was actually 1989?

 

PERFORMANCE


QUESTION: What kind of exhaust systems are offered for the ZR-1?
QUESTION: What's the story on the different spark plugs and gaps?
QUESTION: Do after market chips really make a difference?
QUESTION: Does moving the MAT sensor help in performance?
QUESTION: Does installing a lower temperature thermostat help performance? 
QUESTION: What kind of Dyno results should I see if I Dyno my ZR-1?
QUESTION: When do the secondaries open on a ZR-1?
QUESTION: EPROM & Learning Procedure
QUESTION: I've heard that early ZR-1, 90-92, exhaust manifold were better than later model, 93-95, manifolds?
QUESTION: Did GM build any right hand drive ZR-1's?
QUESTION: Why do stock fuel injectors go bad and leak?
QUESTION: Does Plenum & Injector Housing porting make a hp difference?
QUESTION: Can I use the 405hp heads on a 375hp LT5?  

 

MISCELLANEOUS


QUESTION: What's the best way to store tires?
QUESTION: Why do Corvettes have orange peel in the paint?

QUESTION: What is this active suspension on the ZR-1?

 

MAINTENANCE


QUESTION: How do you reset the Change Engine Oil light?
QUESTION: How come I can't purchase an original ZR-1 battery?
QUESTION: I'm getting noise over my radio?
QUESTION: I'm hearing a strange rattle sometimes at certain RPM's?
QUESTION: I'm getting a squeal from my clutch?
QUESTION: How can I tell either the coolant temp or oil temp from the analog gauges?
QUESTION: My ZR-1 runs hot, anything I can do to improve this?
QUESTION: I need to touch up my '94/'95 wheels, what color paint do I use?
QUESTION: I'm having problems with my INFL REST light coming on.
QUESTION: What happens if I remove all my Low Tire Pressure sensors?
QUESTION: Sometimes I have problem with my ZR-1 not starting.
QUESTION: The feeling of loss power under heavy acceleration or in hard high speed turns.
QUESTION: Can the surface of the flywheel for a ZR-1 be machined?
QUESTION: Why is the cost for the valve cover emblems so expensive?
QUESTION: How good is the clear coating on our wheels?
QUESTION: How do I know if the odometer hasn't been changed or the ZR isn't a salvage?
QUESTION: What if I need a brake job, what should I look out for?
QUESTION: I'm having a problem with my ZF 6-speed transmission, how do I repair this?
QUESTION: How do I enter diagnostic mode for my A/C and how to get digital readout of various engines parameters and settings
QUESTION: I have an oil leak somewhere?
QUESTION: My oil temperature sensor is a 3 terminal sensor but the shop manual shows only 2 terminals?
QUESTION: My ZR-1 gear shift knob rattles?
QUESTION: When I removed my LTPWS from my wheels I get a code 99?
QUESTION: It seems my Bilstein shocks are leaking, are they bad?
QUESTION: Why is my clutch pedal at a different height than my brake pedal?
QUESTION: I hear a lot about different after market brakes, how do they compare?
QUESTION: Are head gaskets a problem on the LT5?
QUESTION: Can the ZR-1 dual mass flywheel be machined?
QUESTION: Bilstein shocks are expensive to replace. Is there a way to rebuild them?
QUESTION: My ZR-1 stalls after a few minutes or when the temp reaches 177 degrees?
QUESTION: How does one pop out the opening to the non functioning exhaust outlet in an early stock ZR-1?
QUESTION: I'm seeing a loss of platinum pads from my spark plugs?
QUESTION: Can I put Dex-Cool in my ZR-1?
QUESTION: Why does the LT5 have two different PCV valves?
QUESTION: Can the starter in the ZR-1 be rebuilt?
QUESTION: What is the best way to jack up a ZR-1?
QUESTION: Why do I see oil in the plenum area?
QUESTION: How do I replace the battery in my ZR-1?
QUESTION: What type of thermostats do ZR-1's use and at what temps do they run?
QUESTION: How do I reset the security code in my radio?
QUESTION: Outside of GM where can I get a new key made?

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QUESTION: What is a ZR-1 Corvette and how do I recognize one?

ANS: ZR-1 was an option package (RPO ZR1). The option included a new high performance engine called the LT5. The option also included a change in the body panels from the doors back which made the ZR-1 3" wider in the rear than the standard model Corvette. This extra width was needed to accommodate the new wider tires (Goodyear Z-rated P315/35ZR17) on 11" wide wheels. You also got a new specially laminated "solar" windshield. Option RPO's that were included standard with the ZR1 package were AC1, AC3, AQ9, FX3, LT5. The 6-speed transmission was required also.

 

It can be a little difficult to tell the difference between a ZR-1 and the standard L98/LT1/LT4 Corvette. But here are some clues:

 

1. All ZR-1s are coupes.

2. All ZR-1s have the 3rd brake light on top of the hatch or roof area.

3. All ZR-1s are 6-speeds

4. From the rear all ZR-1s have a ZR-1 emblem in the right rear corner.

5. From the rear all ZR-1s have a 1 1/2" spacer between the license plate and the back up light.

6. All ZR-1s have 315/35ZR17 tires and 11" wheels in the rear.

7. Inside all ZR-1s have a "power key" on the center dash below the radio.

8. All ZR-1s 1992 and up have a ZR-1 emblem on the side of the hood.

9. All ZR-1s have a special solar windshield glass with a cutout at the bottom middle for using "garage door openers" or in actuality radar detectors.  (Not a heads up display)

10. All 1994 and 1995 ZR-1s have the new 5-spoke wheels.

11. All ZR-1's have a unique VIN number 1G1YZ vs 1G1YY.

12 All ZR-1s have a 8,000 RPM Tach vs 6,000.

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QUESTION: What is different about the ZR-1 engine?

 

ANS: The ZR-1 engine or LT5 was an all aluminum block and cylinder heads, 4 overhead camshafts, 32 valves 350 cu. inches V8. The HP rating was 375 at 370 ft lbs of torque from 1990-1992 and 405hp at 385 ft lbs of torque from 1993-1995.

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QUESTION: I heard the LT5 engine in the ZR-1 wasn't design by GM?

 

ANS: Not totally true, the LT5 was designed by both GM and Lotus.

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QUESTION: How many ZR-1's did GM build?

 

ANS: GM built a total of 6,939 ZR-1s. The first year, 1990, they built 3,049, in 1991 they built 2,044, 1992 502, in 1993-1995 they built 448 each year.

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QUESTION: I understand there was a horsepower increase at some point?

 

ANS: Yes in 1993 the hp went from 375hp to 405hp with cylinder head and valve train changes.

 

Some of the highlights were:

 

Revised back angles of the valves.
Multi-angled inlet and exhaust seats
Head work to increase flow
Revised exhaust cam timing
Revised injector housings and injectors
Altered plenum for increased flow
Smog Changes
Reduced rotating mass of all major components
4 bolt cylinder case
Valve retainers
Revised PROM
Oil system improvements.
Platinum Spark Plugs.
Synthetic Oil.

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QUESTION: Are all ZR-1's the same?

 

ANS: Almost, the first year (1990) was the most unique. The front end had the older style design (same as the base Corvette) while the rear had the new rounder tail you see today as well as the new "square" taillights. The early '90's also had steel half shafts in the rear vs aluminum later. The windshield is also a little different as the clear opening for "radar detectors" is bigger. In 1991 all Corvettes had the new ZR-1 style rear and a new front end. Other changes over the years included different wheels, tires, PKE system, 40th Anniversary package, passenger side air bag, etc. Also in 1993 the Hp rating changed from 375hp to 405hp. This was done by additional tuning to the engine and exhaust system. Like optimizing the induction system by creating a slight increase in valve overlap (4 degrees) and a slight reduction in exhaust back pressure (2" Hg). Emission and fuel economy gain was achieved through calibration improvements and the use of linear EGR which was first used on a LT-5. Plus at this time GM went with 4 bolt mains to increase stiffness and rigidity. The load spread over 4 fasteners. Therefore, assembly stress was lowered allowing the engine to tolerate higher operating loads.

 

Suspension tuning changed in '92, reduction in front spring rate from 96.2 N/mm to 75.4 N/mm, reduction in rear spring rate from 39.9 N/mm to 33.0 N/mm. Tires went from Goodyear Gatorbacks to Goodyear GS-Cs.

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QUESTION: When was the last ZR-1 built?

 

ANS: The last ZR-1 was built on April 28th 1995 in Bowling Green, KY. It was then driven to the Corvette Museum in Bowling Green where it's on display.

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QUESTION: Why did GM stop building ZR-1's?

 

ANS: Several reasons, one was because of low volume.

 

Second, after GM came back with the LT-1 which produced and honest 300 hp, the performance narrowed between a stock corvette and the ZR-1. Because of this sales dropped for the ZR-1.

 

Third, GM did not do enough to differentiate the ZR-1 from a regular corvette. When you pay double the price for a corvette you want people to know what you got.

 

Fourth, the LT-5 was a very expensive engine to produce and GM was in the development of the New Gen Three V-8 which would (over time) produce similar hp at a significant cost savings which GM could pass on to the customer.

 

Fifth, EPA rules meant having to engineer OBD 2 in to the car and that was another expense.

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QUESTION: How fast are ZR-1's?

 

ANS: That is a hard question to answer. Performance numbers vary from ZR to ZR because not every engine built on an assembly line will all have the same horsepower. The LT5 in the ZR-1 will vary from 355 to 414 for example in the 1990 - 1992 375hp cars. Then in 1993 - 1995 the hp went up to a rating of 405hp. Then of course once on the track things like weather conditions, track conditions and driver can affect results. But on average a ZR-1 will do 1/4 mile times around 12.9 at 110mph and 0-60 in 4.9 to 5.2 seconds. I have seen stock ZR-1's do the 1/4 in 12.5 and some in 13.7.

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QUESTION: Can any Chevy dealer work on a ZR-1?

 

ANS: Yes and no. For the most part the ZR-1 is a standard Corvette. The main difference is the LT5 engine. In order to work on the LT5 the dealer had to be "ZR-1 Certified" meaning they had to send someone to ZR-1 training and purchase special tools to work on the LT5 engine. So if you don't have a LT5 problem then take your ZR-1 to any Chevy dealer. But if you have a LT5 problem then you should look for a ZR-1 certified dealer to work on your engine.

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QUESTION: How much was the ZR-1 option?

 

ANS: The ZR-1 option was from $27,000 to $31,000 depending on year.

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QUESTION: Could you buy a ZR-1 convertible?

 

ANS: No, GM never offer a ZR-1 convertible.

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QUESTION: Could you buy an automatic ZR-1?

 

ANS: No, all ZR-1's were 6-speeds only.

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QUESTION: I heard that the LT5 wasn't built by GM?

 

ANS: Correct, GM, because of small volume of LT5 engines, went outside GM to find someone to build the LT5. They chose Mercury Marine because of their reputation in building aluminum engines.

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QUESTION: What is that little cut out I see in the bottom of the windshield?

 

ANS: GM used a special solar windshield in ZR-1's to cut down on solar heat. But this special windshield also blocks "radar" waves from coming though which affects the reception of radar detectors. So GM created this cut out in the solar glass so that owners would have a place to install their radar detectors.

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QUESTION: What kind of exhaust systems are offered for the ZR-1?

 

ANS: There are several after market exhaust systems available for the ZR-1. Some of the most popular are:

 

Borla: 2 1/2" Stainless steel pipes with stainless steel resonator and mufflers.

 

Flowmaster: 2 1/2" galvanized steel pipes with galvanized steel mufflers.

 

Desert Development: 3" galvanized steel pipes with a choice of muffler systems including Stormer, Flowmaster, and Walker.

 

Mallet: 3" stainless steel pipes with a choice of muffler systems.

 

Power Effects: 2.75" steel pipes with integral tunable muffler.

 

Corsa: 2 1/2" 304L stainless steel, unrestricted, straight -through muffler design has no baffles or sound-absorbing packing materials that can deteriorate over time.

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QUESTION: What's the story on the different spark plugs and gap?

 

ANS: The '90-'92 LT5's use the FR2LS (now replaced by #41-602) plug and were factory gapped at .035. The '93-'95 LT5's had some changes done to boost the HP to 405 used a tapered platinum plug, Bosch #41-913 and was gapped from the factory at .050. Some owners claim that re-gapping the '90-'92 plugs to .050 gives them better performance. The draw back is that the plugs don't last as long and should be replaced every 10,000 miles. An alternative is to purchase platinum plugs which will give you longer spark plug life for your '90-'92 ZR-1 and gapped them at .050

 

The difference between the 41-907 (907 now discontinued replaced by 913) and 41-913 AC spark plugs. Both are specified for 90-94 but only the 913 is specified for 95. Both plugs are identical except that the 907 came with threads pre-coated with anti-seize and with its porcelain insulator pre-coated with an anti-stick compound to protect the plug boots. GM has found that, because most people apply anti-seize on to threads of plugs going into aluminum heads and because the LT5 spark plug boots run very cool (as opposed to the LT1's which are next to the exhaust) that the anti-seize compound and anti-stick were unnecessary. If one is worried about the boots, use dielectric grease (standard procedure at dealers).

 

Another new plug is the 41-800 which is a single platinum tipped plug, an aftermarket replacement. Other choices include the Rapidfire #5 or the #9 if you drive hard.

 

However you can use the tapered seat platinum plug in earlier ZR-1's. When the LT5 was introduced, the taper seat, platinum plug the engine was designed for was not available from AC. Only the flat seat, conventional unit could be had. So, that's what Lotus, GM and Mercury decided to use. Tim Holland described the plug seat in the LT5 cylinder head, regardless of model year, is a "universal" type and can accept both plugs. The hook is that when you convert the earlier engines to the taper seat plug (a wise idea...better sealing) you have to observe a one-time only torque specification (which slightly reforms the plug seat in the head) then loosen and retighten to a lower figure.
First, torque specifications to use the first time one installs a taper seat plug in a motor previously equipped with flat seat plugs. The first time you install a taper seat plug, 1) torque to 17-23 Nm. 2) back off half a turn or so 3) retorque to 10-20 Nm and use that as the subsequent torque figure. Also should you want to go back to the flat seat plug, you can at any time.

 

What about using colder plugs for racing? Few LT5 racing applications need a colder plug because the 41-907/41-913 are an AC heat range #2 (already really cold). About the only folks that will really NEED a colder plug are those running LT5s wide-open for long periods of time such as dyno testing and road racing (not street/track but race-only). Running a colder plug for drag racing is unnecessary. That said, your single choice in AC for a colder LT5 plug is the FR1LS, a flat seat, heat range #1 plug. While there maybe some even colder choices in non-resistor plugs, use of non-resistor plugs may generate RF interference that will effect the operation of the PCM.

 

Thanks to Hib Halverson, Tim Holland, and Mark Weaver for this information.

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QUESTION: What's the best way to store tires?

 

ANS: The tread and sidewall of tires are compounded to resist deterioration caused by sunlight and ozone. Nevertheless, stored tires should be protected against these and other potentially damaging conditions.

 

GUIDELINES:

 

DO STORE:

* where area is clean, cool, dry, dark and well ventilated but with a minimum of circulating air.
* so that tires on the bottom of a stack retain their shape.
* whitewall-to-whitewall to avoid staining.
* protected by an opaque waterproof covering, if outdoors, but avoid creating a heat box or steam bath.
* where tires are raised off the storage surface, if outdoors.

 

AVOID STORING:

* where area is wet, oily, greasy.
* where subject to extreme temperatures.
* in the same area as an electric motor or other ozone generating source (if there is a question, check ozone levels to be sure they do not exceed .08 ppm).
* on black asphalt or other heat absorbent surfaces.
* adjacent to highly reflective surfaces (i.e., snow covered ground or sand).
* on piers, ship decks or other open unprotected areas.

Storing Tires Mounted on Vehicles:

It is best to store a vehicle on blocks to remove all weight from the tires.

If the vehicle cannot be blocked up from the storage surface, completely unload it so minimum weight will rest on the tires. Keep tires inflated to recommended operating inflation pressure. The surface should be firm, reasonably level, well drained and clean. Do not store on blacktop or oil stabilized surfaces.

 

Move the vehicle at least every three months to prevent ozone cracking in the bulge area and also to prevent a "flat spot" from developing (due to strain from deflection). If tires do develop a temporary "flat spot", it will usually disappear in a short period of time (for example, the first 25 miles of service).

 

Storing Inflated Tires Not Mounted on Vehicles:

 

All of the preceding guidelines apply in this instance. Keep tires inflated to recommended operating pressure.

 

Before Placing Tires in Service:

* Inspect tires to be sure they are clean and free from foreign object.
* Remove any water that has collected in an unmounted tire.
* Check for proper operating inflation pressure.

 

Thanks to Jim Ingle and Goodyear Engineering for the above information.

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QUESTION: How do you recognize a ZR-1?

 

ANS: A couple of different ways. First is by the ZR-1 emblems on the rear bumper and on the later models on either side of the hood just behind the front tires. Second is all ZR-1's are coupes and all ZR-1's have the square tail lights and a roof mounted 3rd brake light. Also all ZR-1's have a wider rear end over the standard Corvette by about 3 inches as well as wider rear tires and wheels.

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QUESTION: Which thermostat is in the ZR-1, 180 or 195 degree?

 

ANS: There has been a lot of confusion on which thermostat is really in the ZR-1. Some manuals say 180 and others 195. The best answer is that your ZR-1 has a 195 that starts to open at 180 degrees and is fully open at 195 degrees.

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QUESTION: Why do Corvettes have orange peel in the paint?

 

ANS: Orange peel is the result of an applied coat of paint (basecoat, clearcoat, or both) that doesn't flow out or level fully. Keeping in mind that paint is basically applied as a liquefied plastic. The cause of peel is that the paint either doesn't stay liquid long enough to completely flow or the material is to viscous to allow it to flow out. In either case, the paint ceases to flow before the surface is completely level. The result of this is a lumpy or lopey surface that resembles the peel of an orange, hence "orange peel".

 

In the US, manufacturers are required to use high solids paints, with a ratio of about 60% solids to 40% solvent. To better flow the paint out, we need to add more solvent. The problem is that the EPA won't let the US manufacturers add additional solvents. These solvent restrictions stem from the EPA's limits on Volatile Organic Compounds 

 

Thanks to Dan Stauft for this information.

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QUESTION: How do you reset the Change Engine Oil light?

 

ANS: 1. Turn key to run, but do not start the car.

 
2. Press ENG MET on the trip monitor, then within 5 seconds, press it again.


3. Within 5 seconds, press and hold GAUGES on the trip monitor. The CHANGE OIL light should flash.


4. Hold the GAUGES or RANGE button until the CHANGE OIL light stops flashing and goes out. This should take about 10 seconds.

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QUESTION: Do after market chips really make a difference?

 

ANS: I think we should first discuss basics here, because I think most of these "chip" discussions are more involved with "mine's better than yours", etc. than realistic expectations. The power production of our engines is a function of many factors, but a few basics dominate. The first and most important factor involves how much air the engine can pump. This is the part of power production that gets most of the attention. Hear me now and believe me later, "more mass of air moved equals more horsepower."


Naturally, the biggest part of this is the actual displacement of the engine. Consequently, everything else being equal, bigger is better. (The builders of the Viper took this one to the bank!) In the same vein, everything else being equal (hard to achieve) higher RPM is better. If volumetric efficiency were constant at all speeds, obviously higher speeds move more air.


This brings up the other main area of concern with increasing the mass of air moved - volumetric efficiency. This is where most people spend most of their effort. This encompasses air cleaners, ducts, head flow, valve sizes, exhaust systems, cam profiles, etc. Some of these areas affect air flow at all speeds; others, e.g. cam profiles favor specific RPM ranges. Again, in all these areas increasing the mass of air flow is the objective since it is directly related to power. Of course, the ultimate in volumetric efficiency is to be greater than 100%. That's exactly where supercharging and turbocharging comes in.


Factors other than increasing mass air flow that are related to power output include compression ratios, combustion dynamics and parasitic losses.


As far as calibrations go, they are only involved when they're wrong. In other words, having precisely the optimum air-fuel ratio is of minor importance. Having the optimum spark advance is of more consequence. However, getting both of these right is not difficult and doesn't vary substantially with the other elements mentioned above. Consequently, with computer controlled systems as used in the LT5, a fairly wide variation of engine basics can occur and the engine will still be very close to optimum full throttle fueling and spark advance. Therefore, for full throttle power the prospect of magic increases through calibration changes is unlikely.

 

Thanks to Jim Ingle from GM Power Team for the above information.

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QUESTION: How come I can't purchase an original ZR-1 battery?

 

ANS: It seems that the original battery (75Z-72) has been discontinued by AC-Delco, General Motors and the authorized "upgraded replacement" is now (75B-84). This replacement battery is a Delco Freedom 84 series battery and is warranted for 84 months from the date of purchase as compared to 72 months for the original. It also has an increase in CCA (Cold Cranking Amps) of 735 CCA as compared to the original 690 CCA. The new battery is noticeably heavier, has a black case, and raised reinforcement ridges on both ends. The label is slightly different in color & number, but all else is the same.

 

From ACDelco:

 

The correct battery number, with the eye at the opposite end, is battery number 75A-72. Part number 75Z72 has been discontinued.

 

Thanks to ACDelco Customer Assistance for this info.

 
UPDATE 1/31/00: A newer battery has been introduced for the ZR-1, 75-7YR. The hydrometer eye is placed in a standard position on the 75-7YR replacement battery. The hydrometer is not a method to check the wellness of the battery. The hydrometer eye is only an indicator to see if your battery is ready for a load test. For a load test to be performed the battery would be disconnected and not in the vehicle, thus allowing the hydrometer eye to be viewed.

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QUESTION: I bought a '90 or '91 and I didn't get an owners kit? What is in this owners kit?

 

ANS: For '90 and '91 GM had a "special" ZR-1 Customer Kit created. It was mailed to the original owners (car registered to) name/address after purchase, but only went to US customers.

 

The kit came in a vinyl wrapped box with the ZR-1 logo and is the size of a pizza box, only higher. Inside it contained:

 

1- A duplicate window sticker.
2- A Leather portfolio with ZR-1 logo and a metal tag with your vin number and or name/vin number.
3- A Photo album/coffee table book (90 and 91 were different).
4- Video tape, again different for 90 and 91.
5- A ZR-1 specific owners manual with ZR-1 logo.
6- A Brass Key ring with ZR-1 logo.

 

On the open market these can sell from $300 to $1,000.

 

Click here to see a picture of a 1990 owners kit.

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QUESTION: Are there any options that are rare on a ZR-1?

 

ANS: There were really only two options, electronic climate control and dual roofs. The electronic climate control was drop as an option in 1991 and became a standard. Very few '90 ZR-1's were delivered with manual climate control. Rumors were around 14 ZR-1's had manual AC.


Something unusual happen in the 1992 model year. An option that was standard in the RPO ZR1 package was dropped 1/2 way though the 1992 year. The power passenger seat AC1 which had always been packaged into the ZR1 option was pulled and had to be ordered separately.

In 1993 GM once again included AC1 as part of the RPO ZR1 option.

 

Not an option but early '90 ZR-1's had steel 1/2 shafts in the rear vs aluminum on all others.

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QUESTION: I'm getting noise over my radio?

 

ANS: There could be several reasons for noise over your radio. Here are a couple of problems that ZR-1 owners have found and corrected.

 

The noise/squeal described is exactly what my 90 did, first to the right rear speaker/amp then to the left rear speaker/amp. When the right rear finally failed (Yes you could turn the radio off/on and the noise would go away but it finally completely failed) I took the assembly out (3-4 screws and a disconnect) and took the amp apart. It was obvious the amp was bad as you could see where the circuit board had gotten hot and the power transistors were fried.

 

The Delco/Bose systems installed in 90 and up Corvettes apparently are prone to a failure in the rear speaker amps. The problems first appear as a loud alternator wine and popping that seems to come from the whole system rather than any one speaker and at first you can turn the system off then on and it will sometimes go away. To troubleshoot you can disconnect the rear speakers one at a time to find the problem. This involves using a screwdriver to remove the speaker covers and disconnecting the wires that come from the radio. After finding which side is bad you can remove the speaker assembly using a 7MM socket. The amp will have one of the following part # 16148750 or 16148752. I have tried various parts houses but these #'s listed as a back order item that nobody had seen in years and were doubtful about getting. They also listed the following as the latest replacement # that they could order 16179367 which has a dealer list of $354 a dealer cost of $285. Since the first #'s are not available I talked to Hamp at Speedometer Service in Atlanta Ga and he will ship at dealer cost to those who are in need. His phone is 1-800-241-2385 and he will take VISA/Master. If I get any other information I will post it. Hamp is very knowledgeable on these systems and does rebuild dash units as well as the radios.

 

Another possible problem could be an alternator. A "high-pitched whine" suggests possibly alternator produced noise. And the note that it goes away with the engine off relates to that possibility as well. Alternators can deteriorate to produce RF (Radio Frequency) emissions while continuing to function otherwise, so that may be related. Another whole class of problems with cars relates to "ground faults". If there is a poor (high resistance) path to ground of the radio, it can result in performance loss. A quick check is to temporarily run a wire from the radio case to ground (preferably the battery ground terminal) and see if it affects your problem. If so, consider some more permanent arrangement. Finding and repairing poor original equipment grounds can get messy. I believe the Service Manual Electrical Section shows ground points, so it may be worth referencing (if you have access to one).

 

Other sources for radio parts:

 

-Baker Automotive has the unit you're looking for. Call Kim Baker for prices at 413-596-9475. Baker is a race car driver, so his "used" parts are actually removed from new Vettes he gets and converts to race cars.

 

-Buy a used one out of a wrecked Vette from Roy Landrum Enterprises- 606-586-6218 - Office 513-535-8688 - Mobile

 

-Contact United Radio in NY. 1-800-448-0944 They Do a lot of warranty work for  GM

 

-Brad's Corvettes - via internet at bradscorvettes@flinet.com Price was $100 for speaker and amp.

 

-C&S Corvettes - 1-800-886-5064. $120.

 

-Vette Wrecks - 1-800-462-0123. $150

- Contemporary Corvette (advertises in Corvette Fever and Vette). $75

 

- America Corvette in Atlanta just received 500 new amps. They also purchased new speakers, and radios. They are selling the amps for $60.00 a piece, that's correct $60.00 new. These amps are also higher output, 50 watts vs 30 watts stock.

You can call Jim Bressner at 1-800-377-6793 to order.

 

Past and Present Automotive in Clearwater Fl 813-535-7288 will repair all Bose speaker amps.

 

Another member this with his amps.

 

Several people on the net have expressed a desire to learn more about repairing the Bose speaker amps.

 

There are probably six or seven manufacturers of small electronic capacitors in the world (just a guess). One of the companies apparently manufactured poor quality parts in the 1988-92 era. Time and humidity cause the capacitors to leak electrolyte and fail after a couple of years.

 

I have a 1989 Toyota Supra and the stereo went bad a couple of years ago. The stereo in my sister's '89 Supra also went bad, as did the stereo in a friend's '91 Supra and all of the Supras made during that time period. I took my Supra to a radio repair shop and the guys were intimately familiar with the problem - leaking capacitors. The fix was to replace the capacitors.

 

When the left rear speaker in my ZR-1 recently quit working, I called a local repair shop. They have been very busy the past couple of years repairing Bose amps. The problem is... you guessed it - bad capacitors. My Corvette is a '90 model and Bose apparently bought capacitors from the same manufacturer that Toyota's stereo supplier, Fujitsu, did.

 

There are eight small green colored capacitors in each rear amp that look like miniature Sprite cans. I replaced them all. They are all high temp (105 C) mini radial electrolytics with various capacitance and voltage values. You can get these at a large electronic supply store for $.50 to $.75 each. I bought mine here in Houston at Electrotex (713) 526-3456. If you have never desoldered and soldered anything before, find a friend who has and learn from him. Capacitors are polar, so make note of where the positive and negative sides are connected to the board before removing the old capacitors so that the new ones may be installed correctly. The negative side of capacitors is marked with a longitudinal band.

 

After the replacement, I reinstalled the amp in the beast and the speaker now plays perfectly.

 

Some people have posted on the net that they believe the amps fail due to heat buildup destroying the power transistors. I have heard that the failed boards have brown spots on them with is assumed to have come from overheating. My observation was that the board became discolored (brown) where it was contacted by leaking electrolyte from the capacitors. Anyway, since I have heard that the new style amps have a larger heat sink area than the old style, I exercised precaution and applied some white dielectric heat conducting grease to the two power transistors where they contact the metal cover. The stamped sheet metal amp cover serves dual duty as a RF shield and heat sink. By the way, the high temp capacitors are made to withstand 105 degrees C, which is pretty darned hot.

Thanks to William Barrett for this info.

 

FROM AMP OPTIONS:

We at Amp Options have a product you might be interested in. We have developed an amp to replace the Bose* type amp in car stereo's 84 and up with minimal install hassle. In fact, with 91 and up simply remove bad Bose* type amp and plug our amp in. Pre 91 requires chopping of the wire harness and connecting with a connector supplied by us. Each amp is built and tested in the USA and comes with a two year limited warranty. Amps come in a box of twelve at $79.95 per amp, connectors are $3.29 apiece and also come in a box of twelve. Each amp is individually boxed and comes with instructions on installing the product. Every amp comes with a gain adjustment to synchronize the volume with current factory amps still in the vehicle. Any order $2,000.00 or more is shipped prepaid. If you would like to deal in volume please contact me to discuss the price further. Thank you for your time, if you have any questions or comments contact me at:

e-mail at: loki251638@aol.com or call between 8:00 AM to 9:00 PM EST at 770-638 0359

 

Sincerely,
Michael Knoll
Factory Representative

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QUESTION: I'm hearing a strange rattle sometimes at certain RPM's?

 

ANS: It's always difficult to describe noises and to understand what the description means. A possibility is a rattle from an exhaust system heat shield. You may have a loose, missing or broken fastener or the part may have shifted such that it's contacting another part. These rattles tend to be very "peaky" so they occur in a very small RPM window.

 

Another possible reason could be the dual mass flywheel. The dual mass flywheel is just what the name implies. It's two flywheels connected by a spring damper system. The engine crankshaft bolts to the forward flywheel and the clutch attaches to the rear one. It does not change position with speed but it does "wind up" with torque. It's purpose is to control transmission gear rattle. Replacing the flywheel with a conventional single mass flywheel will result in a very high level of gear rattle.

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QUESTION: I'm getting a squeal from my clutch?

 

ANS: The problem you're most likely experiencing is a noisy crankshaft pilot bushing. There is a later design released for service that tends to retain grease better than the one you have and therefore doesn't squeal when cold. Unfortunately, the transmission has to be removed to access the bushing, so it's not a minor repair although the part cost itself is trivial.

 

In the event you're not familiar with these parts, the input shaft to the transmission is externally spined to connect to the inside spine of the clutch disk. The forward tip of the transmission shaft is a smooth section that is located radically by the bushing in the end of the crankshaft. When the clutch is engaged (foot off the pedal) the transmission input shaft turns with the crankshaft, so there's no relative motion. However, when the clutch is released (foot on the pedal) such as when you're at a traffic light, the transmission shaft is not turning and the crankshaft is. This is when the squeal would occur with a dry bushing.

 

The new bushing has grooves in it to help it retain grease and it seems to have solved the problem.

 

Thanks to Jim Ingle for his input.

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QUESTION: How can I tell either the coolant temp or oil temp from the analog gauges?

 

ANS: See chart below:

 

Percentage
of Scale 
LT5 Oil Gauge
READING | ACTUAL 
Coolant Gauge
READING | ACTUAL 
0 %  100 deg F | 100 deg F  100 deg F | 100 deg F 
25 %  -------- | 191 deg F  -------- | 184 deg F 
50 %  -------- | 220 deg F  -------- | 210 deg F 
75 %  -------- | 246 deg F  -------- | 232 deg F 
100 %  280 deg F | 280 deg F  260 deg F | 260 deg F 

 

Thanks to Gordon Killebrew for the chart.

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QUESTION: My ZR-1 runs hot, anything I can do to improve this?

 

ANS: For some applications it is known that the stock ZR-1 cooling system has proven to be inadequate. This has been born out through observations by many individuals on the ZR-1 Network. Various options have been explored with one option, two suppliers, proving the be the most viable fix to over heating.

 

The larger radiator from Doug Rippie Motorsports and the unit from Lingenfelter Performance Engineering both have proven themselves to be very well made pieces of equipment. They do an excellent job at keeping engine temperatures in a very comfortable zone under the most extreme conditions of operation. Typical operating temperatures run in the 90c-97c range, the upper end under track conditions. This is well below the 112c temperatures witnessed by several people.

 

With many members of the ZR-1 Net having installed one of these units, not one disparaging remark has been made, only glowing reports. We all highly recommend one of these units in addition to a Doug Rippie modified thermostat. In bang for your buck, this is one of the best values you can possibly do.

 

Thanks to Jim Milstead for this information.

 

More important for proper cooling, is a clean and unobstructed radiator, and possibly a modified prom calibration. Take a half day and remove the top shroud of your radiator from the top. Look down in between the AC condenser and the radiator and you'll be shocked. If car show judges could find a bent up mirror to get down in there, all you waxers would be in misery! It's filthy! As Corvettes are bottom feeders, we've found that the radiator's airflow is severely obstructed in many cars. This is not visible from the bottom but sometimes you can see a little through the oil cooler line cut outs in the passenger side of the shroud.  We've also made a pipe that screws onto a hose that is about 3 feet long. At the end, we put a 90 deg. elbow. After the shroud is removed, this pipe can be used to "reverse" flush the radiator fins with water. This will help. Just for info: We've also found that most ZR1's out here in furnace land will gradually start overheating after 3 to 4 years no matter what. With the addition of a new radiator, they run cooler than ever. Adding a Stant t-stat and recalibrated prom helps even more.

 

Also the stock cooling fans were manufactured with several air holes in the case. Wet climates or washing the shroud area will allow water to settle within the electric motor. Along with dirt and dust, this causes the motors to get weak over time. The new motors, part number 15-8484, do not have any breather holes and are a sealed unit which eliminates this problem. In addition, I believe they turn more RPM's.

 

You'll also want the new blades 15-8468 which flow much more air than stock.

 

Thanks to Jim VanDorn for this info.

 

More on cooling........

There is a coolant bypass device in the stock ZR1 cooling system which does compromise the cooling ability of the package, the same is true of the oil cooling system. My recommendation is to install an aftermarket radiator with sufficient flow capacity to cope with the 100 USGPM that the water pump is capable of. But I would strongly advise against altering the pressure setting of the radiator since the system is very sensitive to pressure variation. The typical failure mode with either too little or too much pressure is material erosion in the pump itself (caused by cavitations) and also in the cylinder liner and seat areas caused by nucleate boiling. Which is basically small pockets of super heated coolant near the metal surface flashing to steam and eating away at the part in question. During its development phases the LT5 was run at several dyno facilities other than Lotus, each time we had to ensure the correct parameters for the cooling system or holes would appear in the early running life of the engine. So if you wish to change the system pressures be warned, puddles of coolant may be prone to appearing on the floor and/or the oil level in the pan may rise.

 

In so far as the oil cooler is concerned, the stock unit is not capable of dealing with the heat rejected to the engine oil at sustained high speed operation, no matter when the waxstat opens. So fit a cooler that is and then it doesn't matter where the stat opens since the cooler is capable of coping with the heat rejected by the engine. If people insist on earlier opening of the oil cooler lines then simply buy and fit a lower temp waxstat, since the unit is pretty similar to many water thermostat devices, this should not be too hard to find. Furthermore there is a constant controlled leak across the valve to ensure that cooler opening in extreme cold conditions does not result in oil pressure loss due to the cold slug of oil being pushed into the engine.

 

P.S. the amount of power to coolant flow rate was 4bhp to 1 gpm as a rough rule of thumb.

Thanks to Graham Behan of Lingenfelter for the above info.

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QUESTION: I need to touch up my '94/'95 wheels, what color paint do I use?

 

ANS: Go to your local hobby store the one that sells plastic models, and get a paint that is made by Tamiya. Its called Tamiya color, Acrylic Paint and the code number is X-11 (chrome silver). Don't worry about the color (chrome sliver) when it dries its the exact same color as the wheel. Just remember to stir the paint and do not shake it.

 

Touch up the ding with a small soft brush filling the ding to just higher than the surface of the surrounding paint. Let dry for 24hrs then lightly buff down with some polishing compound to the same surface level of the rest of the paint. Be sure that the wheel is cool before attempting to touch it up.

Thanks to Pete Bordonali for this info.

 

Another member has found Testors #1181 Aluminum FLAT ENAMEL in the little tiny bottle (like kids and dads use for model airplane building). It is very close and looks great. And it's cheap - $1.10 at Michaels craft stores. It makes the outside wheel weights almost disappear too.

Thanks to Randy Schulkers for this info.

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QUESTION: I'm having problems with my INFL REST light coming on.

 

ANS: Well, it seems as if all us 90 owners have experienced the famous "INFL REST" problem. I have also had the problem, and in my case I was able to fix it for free. Mine was a code "25" which is a "Front Sensor #2 (RH); Open Circuit". The most likely reason for this failure is corrosion under the sensor. The reason for the corrosion is AC accumulator run-off. The water drips down from the accumulator and runs down the frame rail to the sensor. It wicks under the sensor, and corrodes the bolts and holes. This opens the connection to ground, and creates the error #25 condition. Mine goes out each summer (when I'm using the AC) and I have to re-clean the connection. Here's the procedure to fix.

 

1. Read the stored codes. (They remain, even after a battery is disconnected)

 

1a. Turn ignition switch to "Off". 1b. Ground ALDL terminal "K" to ground ("A"). Consult the manual pg. 9J-A-3 for picture of ALDL connector. (Too hard to explain)

 

1b. Turn ignition switch "On".

 

1c. The flashes of the "INFL REST" indicator lamp correspond to the digits of the two digit malfunction codes. Code 12 will be displayed three (3) times, followed by any other codes, which may be stored. Each code will flash three (3) times. After all the codes are displayed, the sequence starts over with "12" again. If you have a code "25", you can proceed. Here is a total listing of all the codes;

 

14 Front Sensor #1 (LH); Short to Ground

15 Front Sensor #1 (LH); Open Circuit

16 Front Sensor #1 (LH); Sensor Fault

24 Front Sensor #1 (RH); Short to Ground

25 Front Sensor #1 (RH); Open Circuit

26 Front Sensor #1 (RH); Sensor Fault

31 Inflator Squib; Current leakage to Battery

32 Inflator Squib; Current shorted to battery voltage

33 Inflator Squib; Current leakage to ground

34 Inflator Squib; Current shorted to ground

35 Inflator Squib; Open circuit

36 Inflator Squib; Squib fault

41 Indicator lamp circuit; Shorted to battery or ground

42 Indicator lamp circuit; Open circuit

51 Diagnostic unit faulty

52 Firing sequence confirmation set

53 Firing current confirmation set

54 Squib current has flowed

 

2. Disconnect the battery. (You don't want the SIR to fire when your working) You should also wait 30 minutes after disconnecting battery before working any SIR problem.

 

3.Remove the passenger side front tire.

 

3a.Remove the rear inner wheel well. It has an assortment of Torx and hex head bolts.

 

3b. You will now be able to see the sensor, which is mounted on the frame rail. (It is located towards the back of the wheel well area. The box is around 2x3".

 

3c.The sensor has 2 different bolts securing it. (13mm and 10mm I think). Remove them (Yes, it's is very hard to get the rear one out).

 

3d. Carefully work the sensor forward out of its position. The cable has some slack, and will allow a few inches of movement. It is just enough to get the sensor up out of the way, to allow for cleaning.

 

3e. Once removed, you can clean up the surface and apply some dielectric grease to the surface to keep the water out. Make sure you clean both the frame and the sensor. Mine was very wet and greasy. The main grounding comes from the bolts, so make sure they cleaned up. If the bolts show a lot of corrosion, replace them.

 

3f. Carefully reassembly everything. The back bolt again will be a real bear.

 

4. Re-connect the battery.

 

5. You must now clear the codes. (You may want to try this first, as the water may have evaporated. Sometimes my codes will go away for months, after simply clearing the codes.

 

5a.Turn ignition switch to "Off".

 

5b.Ground ALDL terminal "K" to ground ("A"). Consult the manual pg. 9J-A-3 for picture of ALDL connector. (Too hard to explain)

 

5c.Turn ignition switch "On".

 

5d.The codes will flash as before.

 

5e. Wait for the fault codes to flash. (Approx. 5 seconds). When they do, unground ALDL terminal "K" for 3 seconds +/- 1/2 seconds. (The timing here is critical, and you may have to try a couple of times). After ungrounding; ground it again for 3 seconds +/- 1/2 seconds. Unground again and wait 10 seconds.

 

5f.Code 12 should now be the only fault. If not, redo section 5 again.

 

It has been a while since I have performed this procedure, so use at your own risk.

 

Thanks to Mike Zeeff for this information.

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QUESTION: What happens if I remove all my Low Tire Pressure sensors?

 

ANS: For the 1990 and 1991 ZR-1's nothing. You will not see any error indications on your dash. It'll be as if you never had the LTPWS option.

 

For 1992-1995 ZR-1's your LTPWS error light on your dash may light. Telling you your system has malfunction. Whenever you remove all 4 wheel sensors you will get a code 99. It may not appear right at first and can go up to 200 miles before it turns the light on and sets the code, but it will happen. There are two things that can be done and both require removing the DIC.

 

One is to remove the 2 lights in the upper right hand corner of the DIC and the other is to unplug the module. This can be done by using a hook to fish the connector out to where you can unplug it.. The module is attach to the right side of the speedo cluster and can be seen through the hole behind the DIC. It has a pink wire and a black wire going to it, after 91 there is a third wire, tan.

 

The easiest thing to do is to remove the DIC and remove the 2 light bulbs or you can also remove the cruise control fuse, which will also disable illumination of the LTPWS lights; of course, that option disables the cruise control function.

 

Thanks to Jim VanDorn and Jerry Watts for this information.

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QUESTION: Sometimes I have problem with my ZR-1 not starting.

 

ANS: Could be one of several problems.

 
1. The VATS system.
2. A starter problem.
3. The clutch safety switch.

 

For number one, VATS, a quick way for a technician to diagnose a VATS problem is to hook up a Tech 1 scanner. When the vehicle fails to start, display the VATS parameter and note what it says. If it says "VATS enabled" then you've tripped the VATS system and have eliminated other possibilities. This will reset itself after 5 minutes provided NO OTHER ATTEMPTS TO START, OPEN DOORS, ETC OCCUR. A common cause of the VATS problem is the ignition cylinder, which has been updated. If this occurs, change to a new (spare) key and try it. Also, if the VATS system is the problem, try unlocking the driver's door with the door key a couple of times. As most of you already know, the door key switch deactivates the UTD alarm and this switch is known to go out after time (it's obviously the most used).

 

Also note if the security light is on while trying to start the ZR-1. If it is then it's your VATS system. Also if you wait 15 minutes and then try to start it and it starts that also says it is your VATS system.

From Jerry Watts: If the ccm sees the wrong resistance or no resistance when the key is turned to the start position it will set a code 54. Any time there is a ccm code that is active your cluster will flash. If the vats system fails, it will not turn on the fuel pump when you first turn the key on, this you should be able to hear; also you could not push start the car because of no fuel and the injector will not be pulsed.

 

For number 2, the starter, the most probable problem is that your starter has gotten wet. Have you rinse down the engine lately? If it is the starter, then you should be able to park it on a hill and turn it off, try the starter and if it doesn't start, then jump start it by rolling a little. This eliminates the PASS Theft deterrent system and leaves either the clutch safety switch, or the starter itself.

From Jerry Watts: G.M. issued a bulletin back in October of 92. While working at the action center we received a lot of calls concerning this problem. If you wash your engine or are in a high humidity area the starter can corrode because of its location. Later the drain hole size was increased to help with this problem but, it was found this was not a 100% cure. The starter can be taken out and cleaned and put back if you wish.

 

For number 3, clutch safety switch, to check the clutch safety switch use an ohm meter to make sure the switch is opening and closing right or the real fix for this problem is to remove the switch, re-crimp the wire connectors going to it, then re-install the switch. In many cases this should fix your starting problem.

 

Thanks to Jim VanDorn for this information.

 

Note: From another member on checking clutch switches. There is an easy way to check the clutch safety switch, assuming the starter isn't starting. Set the parking brake, put the shifter in neutral, and watch the voltmeter while you turn the key to the start position. The voltage will drop slightly. While holding the key in start , release the clutch pedal. If the voltage goes up and down in response to clutch pedal movement, the clutch switch works.

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QUESTION: The feeling of loss power under heavy acceleration.

 

ANS: There can be several reasons for the feeling of loss power. One is the collapse of the air duct. But another possible problem as written by one of our members.

 

Since we are on the "loss of power" subject I thought it might be helpful to share an experience that I had a couple of months ago. I also experienced "loss of power" under heavy acceleration - she (LT5) just won't hookup. In addition, I also heard a "moaning" kind of noise that really sounded like a vacuum leak. So my mechanic, spent a couple of weeks, off and on, chasing the vacuum problem. He ended up replacing all of the vacuum hoses, tubes and MAP sensor, even those under the plenum.

 

None of this helped and the problem persisted. We did notice something, though, that when he pulled the plenum and looked at the secondaries it looked like they had not been operational in a while. As a last resort we called Jerry Watts and Gordon Killebrew. Yes, they diagnosed the problem - damaged fuel pump. Many thanks to the guys.

 

Solution: (or my understanding of it) The computer had damaged one of the two fuel pumps and therefore the engine was starved for fuel under heavy acceleration. Hence the loud sucking "moaning" sound. So my mechanic replaced the computer and fuel pump. Guess what.......yep, no more problem. Now she runs like new.

 

Thanks to Lauren Groth for this information.

 

Also on hard high speed turns like on the track you may feel a lost of power which can happen if your fuel tank is less than half full.

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QUESTION: How many 1990 ZR1s were shipped with manual AC (C60)?

 

ANS: A total of 124 1990 ZR1s were built with Manual AC (C60). After 1990 Electronic AC (C68) became the standard.

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QUESTION: Can the surface of the flywheel for a ZR-1 be machined?

 

ANS: The flywheel cannot be machined on the LT5. Get another flywheel and also order the weight kit (which nobody knows about at the dealer) for balancing purposes. You will need to look at your present flywheel and note where the weights are placed in the holes at the outer edge. Insert the new weights in the matching holes of the new flywheel.

 

Thanks to Jim VanDorn for this info.

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QUESTION: Why is the cost for the valve cover emblems so expensive?

 

ANS: Nobody knows, but the 1990 emblems are around $22.00 while all other years are around $125.00. The 90 emblems had a red background behind the bowtie (84-90 emblem) while 91-95 had a black background.

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QUESTION: I understand there is a build sheet somewhere on the ZR-1?

 

ANS: Yes in maybe two places. One on the fuel tank and one in the left front suspension area of the ZR-1.

 

First the tank sheet and build sheet are the same. It's basically a computer generated birth certificate for your car. It has the date/time built (actually its the date the sheet was printed) all the RPO codes, their explanations, and shows all your codes for the suspension components, seat belts, air bags, colors, dealership, the whole works.

 

I've never found one on the interior of a late model, but getting the tank stickers off is not difficult.

 

Start by removing the spare tire and tray from underneath the back of the car.

 

Lay under the car and look between the gas tank and the vertical piece of fiberglass where the rear compartment is. You will see the tank sticker the tank, you can gently remove the paper from the adhesive. How much glue is there depends on how good a mood the guy at the plant was in that day. I've seen some with virtually NO glue, to some that were completely glued on. Sometimes, on some prototypes I've seen, the guys would get cute and write "ZR-1" in the glue. Usually, ZR-1 is written across the sticker in Red marker. Maybe you will get lucky and have had someone at the plant leave a personal note on the sticker. "Kick Ass" and "King of the Hill" are popular themes.

 

It is definitely worth going after.

 

If that sticker is missing for some reason, and you really want to know.....

 

This is supposed to be a secret, but I was never charged with guarding it, so here goes....There are additional copies of the build sheet in the left front suspension area of the car. I'm going to take a closer look at one of the '89s later, but I think if you remove the lower A-arm, and maybe the spring on the drivers side, you can retrieve it. The paper is inside the cross member where it is bolted to the frame. A really bright flashlight will allow you to find it by looking into the oval holes in the cross member from the top (near the motor). You will see the paper in the hole, then you can figure out how to get to it. The only one's I've ever retrieved were by dropping the cross member, but its probably possible to do it without so much disassembly.

 

Thanks to Ed Simmons for this information.

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QUESTION: How good is the clear coat on my wheels?

 

ANS: After working for an OEM aluminum wheel supplier in the capacity of production engineer in charge of the paint process, I can possibly lend a bit of light to the clearcoat durability issue. This problem is not in any way specific to either GM or Corvette, it is an industry wide problem that is being addressed in different ways by the different manufacturers.

 

As a side note, the company that I worked for supplied wheels to GM, Toyota, Mazda, Ford, Nissan, Subaru, and a few other companies. Of all of the companies, GM took the most aggressive approach to solve wheel durability problems found over the last 7 years or so.

 

SOME PROBLEMS:

 

1. Wheels are in the worst possible environment for paint. They get banged up, cut by wheel weights, go through outrageous temperature fluctuations (32 degrees out, you slam on the breaks in a panic stop, wheels jump 100 degrees or so in a few seconds, paint stresses as a result), and get hot brake dust spewed at them constantly.

 

2. Aluminum can be a bitch to paint, especially when the paint is a clearcoat over the machined surface. As you may know, water beads up on aluminum (it is not a really wetable surface). Paint also wants to bead up on the surface - this would be bad. To coerce the paint into sticking to the aluminum, a conversion coating must be applied. The most durable clear conversion coating is chromium chromate (not to be confused with chrome plating). A basic paint process is as follows: A wheel is sent through a pretreatment system (industrial washer) where it is cleaned with an alkaline detergent, rinse, converted either by spray or immersion in an acidic bath composed of chromic acid, accelerators (fluozirconic acid, for one), and etching agents (hydrofluoric acid, for example), sent through a series of counter flow rinses (each rinse is fed from the following stage), and finally rinse with pure deionized water to eliminate spotting. After all of this, the wheel is clear coated with either a solvent acrylic clearcoat (i.e. Japanese suppliers) or powder - polyester or acrylic - clearcoat.

 

3. The durability adhesion (paint film resistance to peeling from a scribe line after being introduced to a corrosive environment) tends to improve with both higher levels of the chromium conversion coating. The problem with this scenario is that the conversion coating tends to turn green or gold as the coating weight (area density) of the coating increases. As such, the ideal conversion coating weight is not always easily attainable when the machined surface is to be clearcoated. On fully color painted wheels and in the painted windows of machined wheels, the suppliers can load up on the chrome since the basecoats will cover the coloration.

 

SOME SOLUTIONS (PARTIAL LIST):

 

1. To ensure a more robust conversion coating, many manufacturers are mandating a deoxidation stage in the washer prior to the chrome stage. This will ensure that the conversion coating is more uniform and therefore more durable. This results in a better substrate for the paint to adhere to at any given coating weights because the weak areas are eliminated.

 

2. Powder clearcoat technologies (the most widely used clearcoat process for wheels) are being switched from polyester to acrylic paints. The acrylics are more resistant to environmental problems, such as peeling and filiform corrosion (this looks like worm tracks under the painted surface).

 

3. Some OEM manufacturers are moving away from clear coating machined wheels and sticking to base/clear wheels (Such as on the later ZR-1s, Indys, Grand Sports, and Collectors) until the problems can be better addressed.

 

<< Does anyone have any suggestions on keeping the clearcoat like new. >>

 

Treat it just like on any other painted surface. I would recommend staying away from the "wheel cleaners", as some of the ingredients of some of these cleaners can cause corrosion problems. This information was supplied by a leading paint manufacturer who tested all of the popular cleaning solutions. I'm not sure which are good and which are bad, so I avoid them all. I simply slap a coat of Liquid Glass on the wheels and keep them clean with a moist rag.

 

Thanks to Dan Stauft for this information.

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QUESTION: How do I know if the odometer hasn't been changed or the ZR isn't a savage?

 

ANS: Odometer tampering....Hmm...This is a tough one to catch on any C4 Corvette...Tougher on the '90 and ups, but all anyone has to do with one of those is swap a CCM out of another car with lower mileage...The only roadblock in the way of that would be the VATS system...However, if someone is going to go to the trouble to swap a CCM, he will likely have the capability to scan the CCM and get its VATS code...It is then a simple matter of cutting a new key (with the existing pattern) with the right resistance...You can look for loose dash screws, but that won't tell you much...

 

The only way to really catch a "clocker" is with the documentation of the car...Get copies of all the previous titles from the DMV.. Get the previous registration slips, look for oil change and maintenance receipts....Find out if it was dealer serviced, and if it was, they can run a complete computer history of all the maintenance, with the mileages....With this information, it should be pretty easy to catch something...Look for the obvious signs of high mileage, such as worn pedals, ripped seats, etc..

I will say, however, that there is potentially nothing wrong with a ZR-1 that has 200,000 miles on it....It all depends on how well they are taken care of...

 

Previous wrecks and salvage cars are another valid thing to check for...The title search will show a salvage history in most cases...It is possible to buy a car with a "clean" title that has been totaled in the past...I think its good that you can, because if you buy such a car, assuming you know it was salvaged, you don't want the hassles of your bank or insurance company not treating the car with its proper value...

 

 Many will argue that a prior salvage car shouldn't have as much value, but personally, I disagree...Many cars get totaled and branded with salvage titles that shouldn't be...It is so easy for a body shop to inflate the damage estimate of a car they don't want to fix, and have it totaled, its pathetic...Whenever there is a hurricane or other natural disaster, for example, many cars with just paint and glass damage get totaled, simply because the body shops can't handle the load, and the insurance companies don't want to spend thousands on a rental car while they wait for repairs to be made...

 

There are also many cars that should be legitimately totaled, but don't get reported to the insurance, and are then sold with good titles, no matter how bad the damage...Unfortunately, cars like this sometimes have the Identification numbers removed and transferred to a stolen car...This is HARD to catch, but only if done properly.....If you have any doubt, look for the hidden numbers on the frame rail, look at the engine and trans numbers...Look at the VIN plate closely....Check the RPO label, and if you have any doubt, check the build sheet...Documentation, Documentation, Documentation....Most car thieves won't bother to change everything.. Unfortunately, some dealers end up with cars like this unknowingly, and then pass them on to the consumer...

 

You should have nothing to fear from a PROPERLY repaired ZR-1 that has been damaged, but you can get some leverage in the price, usually...Here are some clues I've encountered that would indicate that a car has been wrecked or repainted...

 

Look on the inner front corners of the front bumper cover where the wiring for the headlights and parking lights run....Bad repair work always shows up in UGLY wiring...Look for splices, or misrouted harnesses...This is a dead giveaway...Also look at the hardware on the radiator support, hood hinges, etc.. another thing body shops always screw up...Look for cracks in the inner wheel surrounds...look at the shims on the upper control arms...You will notice too many, or too few if bad framework was done....Check the tire wear...Look at the floors for obvious dents or fiberglass repairs...Look for over spray into the engine compartment...Look for paint on the front spoilers...Also look where the gaps in the headlight pods would let paint through to the area underneath...Take out the rear license plate and an inner taillight in the back bumper...If the gas tank, or a taillight socket is the same color as the body, its been repainted...Look under the hatch weatherstrip for paint, check the Federal label on the door, make sure it matches the VIN...If its missing, you may have had the door changed. Look inside the rear compartments for shattered hatch glass...You can never get it all out...Look at the door jambs....Ugly repair work always shows up where the quarters are bonded....Look under the car for anything obvious...Note, some cars had the paint touched up at the plant, so don't automatically assume that over spray means the car was wrecked...

 

If you don't see any of that, more than likely the car was :

 

A) never hurt, or

B) repaired properly....Again, talk to the previous owners, and get DOCUMENTATION....

 

Take a friend along, two sets of eyes are always better than one...

That's a few of my ideas, I'm sure there are more....

 

Thanks to Ed Simmons for this information.

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QUESTION: What if I need a brake job, what should I look out for?

 

ANS: I ran across some interesting research GM-STG has done on brake servicing, specifically brake rotors and customer complaints of brake pulsation or "shudder" above and beyond ABS brake pedal feedback. Brake work is a huge business adding up to about 40% of all auto service work in the U.S. Complaints of "warped rotors", "shudder" and pedal pulsation are generating many of the repair orders. Recent industry investigating shows that much of the work being done to eliminate shuddering is actually making the problem worse causing customer dissatisfaction.

 

Question why shops fail to adequately repair disc brakes?

 

-Service techs need the skills of a trained, experienced machinist to machine disc rotors properly and many simply do not have this level of training.

 

-The fine finish on today's lightweight brake rotors is almost impossible to duplicate on many shop brake lathes, no matter how skilled the operator

 

-Too many lathes in too many shops are poorly maintained. If the arbors are nicked and worn, the mandrels damaged or dirty or the tool holders are not in perfect condition, future trouble with any rotors that are machine on that piece of equipment is a certainty.

 

When does rotor replacement make sense?

 

-In many cases machining rotors can create more problems than it solves.

 

-GM is considering implementation of a new warranty policy that will specify replacement rather than refinishing of rotors that are worn unevenly, badly scored (ie: to a depth of .060-in. or more), corroded or are below minimum thickness.

 

A perfect repair or replacement of a brake rotor is completely negated if the service tech does not use a torque wrench or impact gun with an appropriate torque limiter attached to tighten the lug nuts when remounting the wheel. Not using those tools invariably results in uneven torque on the lug nuts which will *always* cause warping or lateral run out of the rotor.

 

The distorted rotor makes intermittent contact with the pads leading to uneven rotor wear. The thickness variation resulting from intermittent contact is what causes the pedal pulsation. Improper tightening of lug nuts is *the number one* root cause of rotor warpage on all C4s. It is also an issue with C2/3s with disc brakes, but perhaps not as critical a factor due to the thick rotors used on those cars.

 

A recent survey of service techs by *Brake and Front End* magazine shows rotors are being machine in 75% or more of the brake jobs being performed. This means that most service techs are conditioned to always machine rotors during brake jobs...a notion that goes back to the days of heavy disc brakes and asbestos-based pads. Many of these service techs fail to realize that technology is, indeed, changing and that rotors do not need to be serviced every time one changes pads.

 

Many service techs routinely "rough up" the surfaces of brand-new rotors, apparently not knowing that today's semi metallic pads need a smooth surface to be effective. That old practice became inappropriate when the brake parts industry stopped making asbestos-based pads that used to glaze rotors.

 

To add to the challenge, GM specifications in most cases limit runout to just .003-in. on today's rotors and 65-82 rotors ought to be held to .002 in. Precision machining of this kind also requires removal of all visible rust that accumulates on the wheel hub flange or on the hub itself because rust flakes are more than thick enough to cause future pulsation problems.

 

Any service tech or DIY who thinks the rotors they've worked on are machined well should put them to test using a profilometer, a stylus that accurately measures surface irregularities. Rotor faces that look smooth and ready for reinstallation are routinely shown by profilometer testing to be very poorly refinished and out of spec. Current rotors are final-machined during the manufacturing process on precision grinders to ensure proper surface finish, a finish so fine that it is almost impossible to achieve with most of the brake lathes currently in use by the service trade.

 

Lots of information in circulation today has predisposed many people to rotor refinishing rather than simply not doing any thing with the rotors at all or, if there is a problem, just replacing them. A 1994 story in *Consumer Reports* advises readers to "...question whether you really need new discs particularly if the car is new and the discs have not been machined before." As a result of this conditioning, many people will demand the rotors be refinished because they have been taught to do that.

 

C4 service manuals give specific data as to conditions under which rotors should or should not be machined and when they should be replaced. I would advise everyone to consult that information before doing anything with rotors during a brake job. That has always been my policy on brake work.

For example, my 1988 Chevy Beratta *never* in 100K miles and three sets of front brake pads ever had the rotors machined. Each time, I inspected the rotors and measured runout to find all within specs. When it came time to replace the fourth set of pads, the rotors measured under the minimum thickness so I replaced them, too, but I did not machine the rotors before installation. I simply installed new rotors and new pads. My 95 Corvette is not in need of brake service yet, but when it is ready for pads I will observe the same service procedure.

 

Thanks to Hib Halverson for this info.

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QUESTION: I'm having a problem with my ZF 6-speed transmission, how do I repair this?

 

ANS: 1. Send transmission to ZF. They would require a deposit of about $500, and would tear down and inspect the transmission. They would then call you and tell you the diagnosis and an estimate of repair.

 

Labor rate is approx $80/hr. Repairs have run from $1500 to $4000 depending on amount of damage and parts required.

 

ZF America, located in Atlanta, Georgia

Mike Patterson 847-634-3500 ext 263

 

2. Order a rebuilt ZF through GM STO(or could be SPO). Cost of their rebuilt is $3300 and $1850 for the core (a deposit until they have yours back)

 

3. Or go to an independent contractor with ZF that sells both new and rebuilt units - Melrose T-Tops in Illinois.

 

Melrose T-Tops Inc.
4310 Ellwalk
Courtland, Ill. 60112

 

Thanks to Dave Wheeley for above info.

 

Also you can contact one of the 5 regional distributors listed below:

 

ZR51 Performance- is a ZF 6-speed repair shop. Bill Boudreau is very knowledgeable in the repair and care of our 6-speed transmission. His costs are ~60% that of GM/ZF. He also offers fast turn around in as little as 3 days. For ZR-1 Net "Gold" members Bill is offering 10% off any parts used in the repair of your transmission. For more info contact Bill Boudreau at (602) 740-6277 or send him an email at:

 

 bill777@inficad.com

ZR51 Performance
5612 East Almeda Court
Cave Creek, AZ 85331
1-602-740-6277

 

Here's a great article on troubleshooting your ZF transmission.

 

FORTE'S PERFORMANCE TRANSMISSIONS
474 Moody Street
Waltham, MA. 02453
1-781-647-1530

 

CONSOLIDATED TRANSMISSIONS
5606 Carder Road
Orlando, FL. 32810
1-800-578-8726

 

MIDWEST TRANSMISSION CENTER
40312 County 8 Blvd
Zumbrota, Minnesota 55992
1-507-824-2012

 

ALL TRANS PARTS
1814 N.E. Argtle Street
Portland, Oregon 97211
1-800-237-8601

 

Another great source for parts and ZF repairs. White Racing Products has ZF parts as well ZF rebuilds.

 

For more info contact Kurt White by sending him an email at KNJW1@aol.com

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QUESTION: How do I enter diagnostic mode for my A/C and how to get digital readout of various engines parameters and settings?

 

ANS: To enter diagnostic mode, push and hold the fan up arrow and down arrow at the same time until the LCD shows -00. You are now in diagnostic mode and may select any parameter using the up and down arrows. To see the value for that parameter, press the fan "auto" button.

 

Note: A minus sign on the display range means to add 100 to the value displayed. So -155 actually is 255.

 

Parameter Number  Parameter Description System Faults  Valid Values 
One of these will be set if your A/C controls have a LED flashing 00 = no Faults 

01 = Temp door motor circuit fault 

02 = Temp door motor circuit fault 

03 = Ambient Sensor Open 

04 = Ambient Sensor Short 

05 = In-Vehicle Temp Sensor Open 

06 = In-Vehicle Temp Sensor Short 

07 = Solar Load Sensor Open 

08 = Solar Load Sensor Short 

09 = Low Freon Detected 

10 = UART Failure 

Temp Setting  60F to 90F 
In-car Temp Sensor  10 = Hot -130=230  =Cold 
Outside Temp Sensor  10 = Hot -130=230 = Cold 
Sun Load Sensor  Max Light    Max Dark 

L98   38              183 

LT5  115        -110 = 210 

Ignition Sys Voltage  0 = 9 Volts   -155 = 255= 16V 
Engine Speed (RPM / 25) 
Vehicle Speed 
A/C System Mode  00 = Off 

01 = Recirculation 

02 = A/C 

03 = Bi-level 

04 = Heater 

06 = Defrost 

07 = Vent 

10 = Manual Recirculation 

10 
Blower PWM  0 = 0 Volts  128 = 14 Volts 
11 
Program Number  00 = Cold  -155 = 255 = Hot 
12 
Mix Number  -155 = 255 = Cold  00 = Cold 
16 
Coolant Temperature in degrees C 
17 
Solar Correction  114 = Max light  128 = Max dark 
30 
Stored Full Hot value  0 to 50 
31 
Temp Door Travel Range  100 to 200 
34 
Temp Door Position 

                                                    Requested 

00 = Full Hot 

-153 = 253 = Full Cold 

35 
Compressor On Time  .1 second increments 
36 
Number of times below critical time 
37 
Software version number 
 

NOTE: This was from a '91 ZR-1 document and may be different for other years.

 

Thanks to Marc Randolph for this info.

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QUESTION: Does moving the MAT sensor help in performance?

 

ANS: The idea behind relocating the MAT sensor is to delay the onset of air temperature based spark retard. Put in simpler terms the software that controls the spark advance has a modifier applied to it after a certain air temperature that reduces the amount of ignition advance the engine runs.

 

This is done so in high ambient temps you don't run into wouldn't, what you are doing by moving the MAT sensor is to increase the chances of running the engine into detonation.

 

The favorite trick by some tuners is to also move the temperature threshold in the software as well and increase the det sensor limits which means you are running very close to the det borderline all the time.

 

If you live in an area like the southwest for instance, with this set up you run a greater risk of engine damage, LT5's are not prone to piston damage from detonation but do blow head gaskets due to denotation and in extreme cases damage the cylinder head face (I can send you some nasty photos if you like!!!).

 

In short, lots of people do but personally I wouldn't, the problems far out way the gains. Five years of development and testing decided that the MAT sensor should go where it is!

Thanks to Geoff Jeal for this information.

 

From Graham Behan on same subject:

 

The control system, part of which controls the spark timing, of the LT5 is a relatively simple thing by today's standards only 32 K as opposed to over 2mb on some trucks. Basically there is a 8 inj table and a 16 inj table for the spark control along with several algorithms that add or subtract spark depending on sensor inputs. One of these sensors is the manifold air temp sensor (MAT). Since a high inlet temperature can lead to a change in the detonation characteristics of a given mixture we monitor the air inlet temp and modify the commended ignition advance accordingly. Now with a relatively high compression ratio engine, such as the LT5, the rate of applied retard for a given temperature increase is somewhat aggressive. The sensor location in the air horn is not an ideal place, since the surrounding heated metal can soak heat into the sensor and give a false high reading, thereby causing a false retard condition. This placement was largely driven by the philosophy that the LT5 should be a complete assembly by the time it left the production facility, there are many sound reasons that support this approach; checking system integrity and reducing installation time at the vehicle assembly plant to name but two. Now a more representative place to pick up the actual intake air temp is somewhere that is relatively thermal insulated from the heat source i.e. the engine, yet is still in the inlet air flow. So the relocation of the MAT sensor to the filter housing is quite a valid solution since it is measuring inlet air and the high temp protection is in place. However modifying the software to minimize the control system response to a high air temp signal is, in my believe not such a valid solution. Since the protection algorithm is put there for a reason, high inlet air temps = tendency to detonate. With the advances in the modern engine management systems engines are now calibrated closer to the detonation limit of the fuel. Given this it is co