All,
I have a 1992 Corvette Vin P 350 automatic and it has me stumped. Nothing has changed on the way it runs and I have replaced the following. New Opti Spark (TWICE) new GM Unit. New Coil, New Module, New Fuel Pump, New Injectors, New Plugs (Double Platinum) Factory, New plug wires, removed and cleaned EGR works perfect, Checked compression all at 190/200 PSI. Bought Snap-On Scan Tool and checked system. Oh, there were no codes and the check engine light was not on. With Snap- On Scanner I get a (28 QDM fault) Fan relay circuit. Strange since the Fan(s) both work perfectly as does the airconditioner. Other than that nothing shows to be throwing a code. Ohm checked the coil and nothing out of range. Replaced knock sensors. This does not have an ESC box since it is a 1992. The ECM does ECS function. With the Snap- On code reader all readings are within normal and it says it is OK to drive. The timing, sensors, and such all read within normal range per the Factory Service Manual Indications Page. The timing moves advance and retard when the throttle is depressed. I am at a loss and want to correct the problem. The nice people at Vista Chevrolet refused to work on the car. I assume since it is a 1992 and ALDL they did not want to take the time to diagnose the problem since it is not OBDII where all you have to do is plug in and get a code. Oh, in park when it reved it does rev up but slowly and in gear it stumbles over 3000 RPM. It idles like it has a miss but was doing the same thing before I started.