Guys, I'm new here. As you can see from my name, I don't have a third gen, but rather a second. However, it's almost become mechanically more third gen than second! It has a ZZ4 with a Miniram intake and GM 1990 TPI electronics, as well as a TH700R4 trans, Baer four wheel disc brakes, and Corvette LT4 wheels.

Anyway, here's the deal- It was running great up until about a month ago.

There is a horrendous misfire at idle speed which is tracible to the number 2 cylinder. When the #2 injector or plug wire is removed, there is no effect. Other cylinders displayed a noticeable effect on engine speed and idle quality.

I have verified cylinder compression and injector operation. On the ignition side, I have switched cap and wires with another vehicle, but no effect. I have also replaced the HEI module, spark plugs, coil and rotor. In addition, I've verified all sensors are good and that there is continuity in all of the circuits from the ECM outward. The ECM itself is also brand new.

The last thing I looked at was the condenser since a static noise has been audible through the stereo system lately. I replaced the condenser and the problem went away (noise and misfire) for a few minutes but then returned. This is now leading me to the voltage input side of the distributor, which I have yet to check.

One other noticeable symptom is a huge over correction by the computer of the long term fuel- down to 114 at any speed. The interesting thing about this is that the O2 sensor is on the driver's side of the engine (opposite the suspect cylinder). I'm going to install an O2 sensor on the passenger side and use a diagnostic tool to monitor it.

But in the meantime, any thoughts? Because it's driving me crazy.

 

What does the #2 plug look like? The #2 injector could be leaking and making it to run rich. How old are those injectors?

Did you put a fuel pressure guage on it and turn the key on to see if the fuel rail was holding pressure?

You can also lift the fuel rail up and watch the injectors as you turn the key to the ignition on position to see if the #2 injector is dripping without the car running.

 

Yes. Thanks for reminding me. I did verify fuel pressure- 38 psi at idle and about 45 at WOT. I inspected the fuel rails for clogs and swapped the #2 injector with the #1 and the number #7, but no change in the problem. After turning the key off, it holds pressure almost indefinitely.

Also, all of the spark plugs are uniform in color- a light tan, with no weird deposits.

What's funny is, the misfire all but disappears after 1500 rpm. Without the scanner, I'd never know there was a problem above that speed.