A transmitting sensor is installed (by large band type clamp) on each wheel. Each sensor has a separate identification color and frequency which is transmitted as the wheel moves. The movement of the wheel provides the electric power necessary to power the transmitter, therefore, no battery is necessary. This "Piezo-Electric" energy develops after only 30 seconds of operation at over 25mph.
 A receiver module is located within the dash which receives the signal transmitted by each sensor. When the tire pressure is low (below 25psi), the sensor is triggered causing it to stop transmitting. The receiver recognizes the absence and turns on the warning indicator "Low Tire Pressure". If the receiver unit senses any other malfunction in the system such as a sensor that doesn't "report in", then the "Service LTPWS" light illuminates.

 "Service LTPWS" usually indicates a faulty sensor and a code will be stored within the receiver module. The '91-'95 model ZR1's have the ability to be diagnosed and codes cleared through the Tech 1 hand held diagnostic tool, and by the Assembly Line Data Link or ALDL connector. The '90 models do not have this capability. In fact, the '90's diagnostic procedure can be extremely time consuming and basically requires replacing each wheel separately and then road testing until the faulty sensor is located. This can be done with another non-LTPWS equipped wheel or the vehicle spare. Start by replacing one wheel/tire combination and then driving the vehicle. Wait for the "Low Tire Pressure" light to illuminate (ignore the "Service LTPWS" as it will stay on). When the replacement unit does NOT set off the "Low Tire Pressure" light, then you have located the faulty sensor. In all cases, after repairs are made the code(s) must be cleared manually from the receiver. They will not clear themselves.

Important Note #1: Because new sensors cost $150 each, and to avoid unnecessary damage, BE SURE to alert the technician that your wheels contain the LTPWS sensor prior to performing any tire repairs or replacements. The sensor is originally placed 180 degrees from the valve stem, usually marked by an exterior decal.

Important Note #2: There are numerous errors in the service manuals regarding the correct color locations and part numbers for the '90-'92 MY (Model Year) sensors. The correct information is below. Keep it for future reference.

GM #10098494, Right Front-Blue
#10098495, Left Front-Green

On all year models, if the SES comes on during hard acceleration, then most probably a code 61, Secondary Throttle system error has occurred. Test you vacuum pump (located in the right front headlight cavity) by turning on both ignition and power keys (do not start the engine) and disconnecting the secondary vacuum connection coming from the pump. The pump should turn on immediately and run continuously. Place a finger over the open line and the pump should suck down and quit running. Check all other vacuum connections. Particular to the '93 model year, we have seen a tremendous amount of problems with the Exhaust Gas Recirculation (EGR) systems. This may also be compounded by a faulty PROM (Programmed Read Only Memory) calibration. There is an updated replacement PROM available from your dealer.

NNote: When the SES is illuminated, both the cruise control and secondary throttle systems will become inoperative.

Note: Operation of the SIR system will be questionable if the "INFL REST" light is illuminated.

The sensor, which is located atop the oil filter housing, is now available in a new design.

Note #1: Today's fuel pumps are lubricated and cooled by the fuel itself, therefore, a pump that is allowed to run dry may experience a much shorter service life.

Note #2: '93 ZR1's produced between January 1 and mid-February were equipped with a slightly longer filler hose to reduce the filling capacity by 2 gallons. This was a quick fix to remedy a slightly overweight car which did not adhere to Federal certifications. After mid-February, the heavy front and rear rubber bumper absorbers were replaced with much lighter Styrofoam units. This upgrade continued for the entire production of all C4 Corvettes through '96. By removing the sender, an owner can restore the fuel tank to it's full capacity by simply removing the clamp and added rubber hose extension.

Now that our cars have "seen the light" or at least been parked in the sun for a time, many of you may have noticed some strange markings beginning to appear near the top of the windshield. This is the start of the delamination process. Although a regular Corvette, non-laminated windshield can be installed for 1/4th the cost of a laminated one, many choose to keep their cars original, therefore installing another laminated windshield. You will notice however, that all replacements come with a smaller clear window than the earlier models (90-92), but matching the 93-95 original equipment manufacturer's (OEM) style.

The clear acrylic tops are popular especially with the big folks because they provide a little extra headroom. This is particularly beneficial when a helmet is worn. However, when used in aggressive driving situations, the acrylic top may develop cracks mainly because the top provides a major structural support for the C4 Corvette's chassis, therefore, the plastic top is subjected to some fairly strong flex forces. You might notice this flex or looseness when you operate your Corvette without the top in place.

Speaking of seats and headroom, a helpful tip to gain some additional head space is to simply unsnap the front of the lower seat cushion and remove the cushion (all found money should be forwarded to us immediately). Notice the two, 2 inch elastic straps which run front to rear. By simply unhooking these two straps, the seat cushion will settle enough to provide another inch plus of valuable headroom after a brief break in period.

If your system suddenly gets warm, makes noise or emits smoke, then a more dramatic problem has occurred. Compressor failures with the Nipendenso compressor are quite common. The compressor comes separate from the clutch so both must be ordered and are strongly suggested to be replaced as a set. The plenum must be removed for this procedure..

The Corvette AC system is engineered using several types of metals. Unfortunately, some of these metals don't quite like each other all that well. An example is the AC lines which are made of an aluminum alloy but attached with a steel nut to an aluminum thread. In many cases, these lines become frozen to the component (drier or evaporator) causing them to be damaged during the removal attempt.

Don't blame your local technician when this occurs, this is an existing engineering problem. All fittings should be treated with either a teflon tape or anti-sieze equivalent when reinstalled. Although the 90-93 ZR1's were designed using the no longer manufactured R12 type freon, these systems can be converted to the newer R134a freon using basically stock components after a thorough cleaning and resealing operation is performed. Obviously, the best time to consider the changeover is when the system requires a major repair such as a compressor change.

Note: Always have the accumulator/drier replaced when changing the compressor.

One of the few problems we've encountered with respect to wheels is the cracking of the '90 model wheel when used in aggressive track conditions, especially when used with traction enhancing tires. The cracks seem to be more noticeable from the inside of the spokes. It is highly recommended that all wheels be thoroughly inspected before and after use in severe traction conditions or before any high speed operations.

Simply put, if you wash your engine, you will almost certainly damage the starter motor which lies beneath the plenum in the valley of the engine. This condition seems to be more frequent when the engine is hot rather than on cold starts. There is a small drain tube designed to drain excess fluids from this area, however, in a very short period of time, debris causes this to cease functioning. There is a larger tube kit available which requires drilling your block, however, we found that simply keeping the hose far away from the under hood area is usually adequate to solve this problem.

Other occasional no start conditions can be attributed to a faulty clutch switch, VATS (Vehicle Anti Theft System) key cylinder, or ignition switch. A simple test to determine which may be at fault is to attempt to "jump" start your ZR1 when you experience this problem. This is best accomplished by parking on an incline, then turning on the key to the "On" position. By rolling the vehicle to a fast walk speed, then letting out the clutch in second gear, the engine should fire up. If no signs of starting occur, then the problem is most likely VATS related. If the vehicle does start, the problem is in the starting circuit, i.e., starter, clutch switch, etc.

Note: The ZR1 will likely not push start when the battery is completely drained. It should be at least partially charged first.

Second possible issue:

The true bottom line is that the starter solenoid on these cars requires near new battery capacity. The most common no-start condition is that the solenoid does not engage the starter. If your starter engages, engine turns over but the engine does not start, that is a completely different problem. I'll repeat what I have discovered. There are (unfortunately) a series of voltage drops in the starter (solenoid) circuit. Theses include the starter relay ( under the dash ), the clutch switch, battery internal resistance, battery connections and the actual positive batt (purple wire) attachment to the solenoid. Since the LT-5 requires optimum power delivery to the solenoid, high resistance in any of the above mentioned areas can result in a no-start condition. To eliminate all of the arcane segments of the system, simply locate the large purple wire in the wiring harness (behind/next to the ECM in the engine compartment), place the car in neutral, apply the emergency brake, turn on the ignition key, pierce the insulation of the purple wire, and jumper/connect a jumper wire no smaller than 16 gauge from the exposed copper conductor of the purple wire to the positive battery terminal. If the solenoid doesn't engage, be sure that the battery is at full charge. You should see a spark at either the purple wire or + batt terminal when you make the connection. No spark... probably an open circuit, spark but no start... possibly a low battery.

Start... install a start switch in the cabin that bypasses all the resistive areas.

by James Britt

------------------------------

From Marc Haibeck:

If you still have a problem with a new starter suggests that the root of the problem is not the starter. I presume that you have a  battery that is less than two years old. More no start problems are
caused by an old battery than a defective starter.

It would be useful to learn more about what is going wrong. The next time the problem occurs. Remove the driver's hush panel. Carry a volt meter in the car. When the car won't start, connect the meter and measure the voltage on the purple wire that is connected  to the clutch switch. Do this with the key in the start position. The following assumes that the new starter is not the problem.

- If the voltage is about 10, it's likely that the problem is a voltage drop (poor connection) in the wiring before the starter.
- If the voltage is less than 1, it's likely that there is an open circuit in the wiring before the starter.
- The battery voltage must be at least 12 for reliable starting.
- Connect the purple wire to the battery + with a 12 gauge wire. If the starter is good the engine will crank and start.

Part 2:

Here are some ideas on how to sort through an intermittent no crank
problem. This applies only to '90 - '92 ZR-1's. The wiring was improved in '93.

In the shop, the current on the purple wire to the starter can be
used to analyze the problem. The normal starting current on this
circuit is 10 to 12 amps. If the current is higher, there is a short
in the starter solenoid. This is a common failure mode. Often the
starter current will be normal when the engine is cold and too high
when the engine is hot.

If the no crank occurs on only about one out of a hundred starts,
another strategy might be better. Fabricate a jumper wire, 12" long,
14 gage, with male and female 1/4" spade connectors on each end. Plug
one end into the purple wire to the starter on the clutch switch
connector. Remove the aluminum crash panel from under the steering
column. It's attached with four 10 mm head fasteners. Remove the VATS
interlock relay. It's the relay closest to the left side of the car.
There are three yellow 10 gage wires on the relay socket. Plug the
other end of the jumper wire into one of the yellow 10 gage wires in
the relay socket. Crank the engine. Only one of the yellow wire
connections will work. If the engine does not crank try another one.
With this connection, the clutch switch and the VATS interlock relay
are removed from the circuit. The jumper connects the ignition switch
contacts directly to the purple wire going to the starter solenoid.
If the car doesn't crank in this configuration, the starter is the
prime suspect. The VATS, the interlock relay contacts and the clutch
switch are out of the picture.
 

This causes several problems. First, the PCV valves (located just left of center of the rear of the engine) become detached from their respective rubber housings. Secondly, most other vacuum hoses on the LT5 become soft and loose after a period of time which allows them to come loose also. The visible result of this is black smoke (MAP sensor line), and poor performance in general.

In the case of a backfire, immediately inspect all visible vacuum lines and connections. It is possible that vacuum connections under the plenum have also become detached. This may be readily apparent in that the auxiliary vacuum pump, located in the right front headlight area, will operate continuously with the key on. In order to gain access to all vacuum hoses, the plenum will require removal. We strongly suggest either replacement of any loose or oil soaked vacuum lines or at least the use of tie strap retainers used tightly to secure them.

There is no easy way to de-carbon an LT5 without physical disassembly of the engine. Therefore, it is crucial that you avoid allowing these deposits to form in the first place. How? Well, the LT5 is like a race horse that needs to be run and run hard. Good gas and "occasional" high rpm operation are the only known precautions against carbon buildup.

If oil is found around the spark plug, it usually means the internal o-ring sealing the plug tower has failed. This will be cause to remove the cam cover in order to replace the o-rings.

When servicing a clutch assembly, most technicians will see the flywheel's dark spotted appearance and immediately suggest re-surfacing the flywheel. DO NOT allow this to be done. As warned against in the service manual, the dual mass flywheel must not be surfaced. This appearance really does not reduce the clutch's effectiveness or hamper it's operation. Unless you have felt some previous vibration, noise or other problem, leave the flywheel undisturbed. Your flywheel, if original, was balanced with your engine, therefore, a replacement will not be as accurately balanced (see "Other Flywheel Concerns" below). If there are visible groove, etc., on the flywheel, then there is no choice but to replace the unit with a new one available from your dealer for approximately $800.

Also important in the clutch area is the replacement of the throwout bearing and pilot bushing. Do not panic if the pilot bushing is loose within the crankshaft. This is common and a source for many loud clutch related noises. If ignored, the loose bushing may enlarge the crankshaft hole so excessively, the newer bushing will not seat. This will be cause for some creative machine work.

There has been much confusion over which bushing is to be used. GM has changed their part numbers several times and are currently referring to the bearing (part #14061685) to be used. We strongly suggest NOT using this bearing as it is a needle type bearing designed for 6.2L diesel trucks which have a limit of only 4,000-4,500 rpms. You can imagine how fast those little needles will turn at over 7,000 rpms. We have seen some failures which were quite interesting. The ideal bushing replacement is a bronze type with three grooves (or flutes) spiraled inside and is available under the GM part number 10125896.

Special Note: Some of you may have had the occasion to replace a pilot bushing on engines other than the LT5 by filling the hole with grease and then using a punch to force the bearing out by the hydraulic method. This will cause major problems if done on the LT5 as it is a hollow crankshaft with a plug seated at the end. Carefully use the appropriate tools for removal and installation of the LT5 pilot bushing.

When flywheel replacement is necessary, be sure to order some flywheel weights also. By looking at the 28 small holes located near the edge of the original flywheel, you may find these small weights filling several of the holes. This is the original weighting done on your engine during it's initial assembly. BE SURE to place the new weights on the new flywheel in the identical positions. You remember the balancing of a nickel on the LT5 plenum they once did during the ZR1's introduction? Well, that smoothness may vanish if the flywheel is not kept in similar balance.

Although intimidating at first glance, the LT5 engine is really a somewhat technically friendly design. The plenum can be removed by a novice in less than an hour (be sure to first drain the coolant prior to plenum removal). Physically attached to the plenum's underside, you will find four electrical connections leading to the ignition module. It is highly advised that these be treated with care as they can be damaged and can lead to a host of secondary problems.

On the top of the LT5 engine, you will find the AC compressor, alternator, injectors, ignition coils, spark plug wires, coolant sensors, numerous vacuum lines and fittings related to the secondary throttle system, and of course, deep within the valley, the starter.

Helpful hint: So you're broken down on the side of the road and need emergency access under the plenum? Maybe need to tighten a cam cover? In an emergency, you should know that your targa top ratchet is the same size Torx tool as many fasteners on the LT5 engine including the plenum and camcover screws.

Remember, this is just in case of an emergency.

WWe strongly recommend replacing any excessively loud chain tensioners before any other problems occur. The plenum must be removed to replace the left unit and the right is accessible from the right front wheel well.

Suggestion:

When or if your engine's oil pan is removed for any reason, ask that the baffle unit be removed and the pan inspected. Any debris found in the pan can be an indicator of your engine's health.

The earlier style converters have also suffered periodic failures. This can be catastrophic if the catalyst is ingested into the engine via back pressure. When this occurs, cylinder and piston damage usually results. Listen for any strange noises coming from your exhaust or any strange rotten egg smells. This can be a sign of impending cat failure. The older style catalytic/manifold units are no longer available, however, the newer manifold/converter units are available from GM for about $2,000 a set. Unfortunately, because of different flow characteristics, we do not recommend the replacement of just one converter assembly.

Both pumps run from start-up until a certain coolant temperature of ~176-degrees F is reached, then the secondary goes off unless the power key is on and the secondary port throttles are enabled.

Thanks to Erle, Hib, Ed, James, and even Bruce, I've figgured out how to
read Diagnostic Trouble Codes on the 1994-95 MY ZR-1.

The 1994 service manual is confusing on this issue.  It says you cannot read
the codes on cars with the 16 pin connector under the dashboard right above
the pedals.  The reason for this is because the 94-95 LT1 cars were wired up
for OBD II, which was required in 1996.  Since the LT5 was going to be
discontinued after MY1995, there was no OBD II implemented on the LT5, but
it got the 16 pin connector anyway.

I was able to read the codes on my 94 ZR-1 by grounding the #6 pin by
connecting it to the #5 pin.  If you look at the connector, it is
trapezoidal in shape.  The wide part is the top, the narrow part the bottom.
The pin on the top left is #1, the top right is #8.  My ASCII-Art is a
little rusty, but here goes:


Connect these two--+--+
                   |  |
   ----------------v--v----------
   \   1  2  3  4  5  6  7  8   /
    \                          /  <------- connector under
     \ 9 10 11 12 13 14 15 16 /         driver's side dashboard
      \----------------------/



It's simple enough to use an unfolded paper clip to make the connection.

Having done the above, turn the ignition key to the "on" position, but do
not start the engine.  Every relay on the car comes on (except the fuel
pumps), so don't be alarmed if you've never done this.

The "Service Engine Soon" light will flash a code 12 three times.  It will
flash once, then pause, then flash twice, then a long pause, then repeats
two more times.  Code 12 indicates everything is working.  After the code 12
flashes three times, the SES light will flash out any DTCs that have been
set three times each, starting with the highest numerically.  If the SES
flashes four times, then pauses, then flashes five times, then it's DTC 45.
Follow the service manual for diagnosis and corrective action.

Disclaimer:  I provide the above information to save any 94-95 owners some
time figuring out how to read DTCs on their ZR-1s.  Use the information at
your own risk.  If you're not comfortable with that, please take your car to
a qualified technician.

Thought I would pass this on to others whom might be interested in hearing more about the GM Clutch Hydraulic System Actuator (slave cylinder) quality spill issue. Before getting into further details of the quality assurance issue, I would like to explain a few basic details about the different types of clutch hydraulic actuators which are available on the market. GM and NAPA sell the TRW manufactured actuator which is made of a Draw Over Mandrel (DOM) tube construction and has a black powder coat finish. Other companies such as Checker and AutoZone sell the WAGNER manufactured actuator which has a cast body construction. Same goes for the master cylinders as well. Several weeks ago my partner Gregg Creevy and I were dissecting three new DOM style actuators when we found that all of the seals were installed backwards. Based on the previous DOM style actuators installed into customer vehicles which by the way failed within a few hours to a few weeks of operation and how they acted prior to failing, it is our speculation that these DOM type actuators have been having the seals installed backwards for the last two to two and a half years. Getting this information to GM Quality Control Group was the one aspect that we did not know how to do. I called Hib Halverson to ask what he would do. Hib suggested that I call Stan Lorence from Tom Henry Chevrolet Parts and advise him of our findings. As it turned out, Hib was right on the money. Stan went straight to the highest point of contact within GM SPO Quality assurance group. Many thanks to Hib Halverson and Stan Lorence for your efforts in getting this information to the people who can make this problem go away. Also many thanks to Jeff DeBuhr on the Corvette Forum for corresponding with others to make them aware of this quality assurance issue as well as providing GM with a visible queue of public awareness regarding the existence of this problem. The following messages are correspondence sent from Stan to GM SPO and received from GM SPO back to Stan. Thanks again everybody for your help, Stan especially. Sent: Friday, May 26, 2006 4:50 PM Subject: Corvette slave cylinders Hi John, The following was sent to me by one of my customers, Bill Boudreau a nationally know Corvette expert, and appears on the Corvette Forum website. It concerns the Corvette C4 clutch slave cylinder which, in my experience, has a very high failure rate. Nearly half of them sold over the counter are returned to me as defective. Please visit the following web address http://forums.corvetteforum.com/showthread.php?t=1402043

 for an explanation of the failures. These failures have been an issue for over two years. This seemed to me to be an important enough issue that I needed to let someone at GM know. I spoke with my parts rep Casey Rentfrow, who is always very helpful, and he suggested that I email you the information. My customer, Bill Boudreau, has been attempting to procure the affected seals (part number AAD-34665237) without success. He states that they must be highly proprietary because he has access to all the major manufacturers and they cannot or will not supply them to him. He has asked me to approach GM on his behalf and request that these seals be made available. After you review and consider this information I ask that you keep me informed and "in the loop". Thank you in advance for your attention. Thanks Stan Lorence Tom Henry Chevrolet Parts.

Info from Bill Boudreau