ZR-1 Maintenance Tips

General Maintenance

by Jim VanDorn


The most common call we receive by far is from a confused ZR1 owner. After years of reading everything from which thermostat to use, to what type of spark plug is best, the average owner is totally and completely confused...and for good reason. There are many varied opinions of what is best for our cars but that may depend greatly on how you use your ZR1.


After seven years plus, many ZR1's are finally accruing some mileage. We have had the opportunity to closely inspect many engines with a variety of types of use from normal street driving to severe "weekend" use (track time). Compiling this information we can now offer the ZR1 owner some observations. One rule we've adopted after hearing so many owners say the same thing is the "DIMWIT" or "Darn, if I didn't Mess With IT" rule. In other words, if you didn't have a problem, then what are your intentions in the first place? To date, the only company known to have a fleet of engineering ZR1's to test with was GM and it's affiliates.


Therefore, we must ask ourselves if their suggested procedures and parts recommendations should have a considerable amount of merit. Obviously they do, but on the other hand, there are no doubt areas for improvement. Although we will begin our segment discussing the routine and normal maintenance of the ZR1, there are many areas where an upgrade will be suggested.


Please understand that these are personal opinions and experiences and are not intended to conflict with service procedures outlined in the appropriate service manual.

We receive many calls from terrified owners that have experienced a backfire condition on initial start. There is a simple cause of this. You. What happens with the LT5's ignition sequence is the ECM checks the cam and crankshaft positions by their appropriate sensors. The ECM monitors the signal, determines which cylinder is ready to fire and then releases fuel and timed spark which then allows the engine to start. This occurs much in the same way every time we start our cars and frankly, we become so familiar with the exact amount of crank time we eventually anticipate the start up ever so slightly. When we move the ignition cylinder from the "Start" position prior to the engine actually starting, this can cause an out of sequence cylinder to fire with it's intake valves open, causing a "backfire".

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.

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