[QB93Z]

I have a Lingenfelter 368 cuin 1990 ZR-1. I had a noise similar to what you recorded (but not as loud) that made me think it might be a bad lifter or valve.

I had Marc Haibeck listen to the car a BG and he diagnosed (correctly) that the noise was from a torn rubber fitting and a bad check valve in the Air System. I fixed the problem my self.

The Air System is a pump the injects air in to each exhaust runner during the first few minutes of engine operation. It is an emissions related system that helps the Cats get up to temperature quickly.

The system has pipes, Tees, fittings, and check valves that run from the area forward of the left front wheel and runs to the left side exhaust piping, and crosses under the engine to the right side exhaust piping. The fittings and check valves, if they were not removed, should be visible just below the cam cover (easier to see on the left side).

On my engine, there was a rubber tee on the right side that was twisted and split. This allowed the Air check valve to click shut on each exhaust cycle for that cylinder.

Some cars with headers still have the Air system attached to small pipes welded to each runner of the header. (Mine did after Lingenfelter worked on it.)

On a separate issue, I have heard many ZR-1's that have flywheel noise that goes away when the injectors are replaced. It is a common occurance. I am not saying that this is definetly your problem, but it might be worth investigating. There is a procedure to measure the coil resistance of each injector, which may help diagnose an abnormal or failing injector.

You mentioned that you car starts in one second sometimes and 2-3 seconds other times. I consider this normal. The ignition system needs to detect the crack position signal before it will start firing plugs. Start time, therefore, depends on how far the engine has to rotate before the crank position slot passes the detector.

Good luck.

Jim