1994 Z28.
Getting a code 42 after car runs for 10-15 minutes. Tried the testing on shoebox's site. All is well except the AC voltage at the ICM (white wire from PCM) is 11v. When the car is cool (and will run) its 4.6v. Probed Opti to PCM and PCM to ICM wiring for continuity and it's OK. Is there a test to isolate further?

 

A 42 is indicating the white IC wire to the ICM is near 0. Since the voltage comes from the ICM to the PCM, it may be the connection is bad or it's the ICM that is defective. Suggest trying a known good one from another car.

Also look at the body of the coil for holes, splits or tell tale white spots indicating shorting. Since the coil is a tune up item you may want to just replace it.

 

My car had this code(not active, stored) It was missing popping etc.....had a bad distributor cap.


I dont know if they were related, but the cap fixed the car.


I didnt really have a check engine light on, but a few times after the car was started the bulb check of the light would stay on along time then go out.(30 seconds)


David

 

Now getting a code 36 (high res) and a 41 (open from opti to PCM). I'll probably change the opti.

 

DTC 41 = Ignition Control (IC) circuit (open circuit)

DTC 42 = Ignition Control (IC) circuit (shorted or grounded circuit)

Both those refer to the IC Module circuit, and the white control wire from the PCM. They can be related to the IC module, coil, PCM or Opti. There are logic trees in the factory manual to help you work your way through the diagnosis.

DTC 36 is correct as described above, but that can be as simple as a corroded or damaged Opti harness connector.

 

Just an FYI. It was the opti. I tried a summit opti and it wouldn't fit. I couldn't tell exactly why except it looked like the Aluminum tab that fits into the notch on the timing cover was a little bigger. At any rate it wouldn't fit flush and the delco unit slid right on.