MALF: 42 EST GROUND. Any idea what this would cause? I just did a harness swap from a custom harness (87iroc 95LT1). I never had this code before. The only issue I have had with the car so far was on the highway doing a constant 80-90 KPH the car would lightly Buck, I could also see the speedo jump like 4kmph when it happens.

Any Ideas?

Jay

 

Use Shoebox's code list - it is specific to the LT1:

http://shbox.com/1/Dtcs.htm

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

The PCM digests the cam position info from the Opti. It uses it to calculate the spark timing. At the correct instant, it sends a pulse on the white wire from pin A12 of the PCM to pin B of the Ignition Control (IC) Module. If that signal goes astray, or if you have wiring problems related to the IC Module, or if the IC Module itself has failed, you will get that code. It is also possible to get that code due to an Opti problem.

The best way to diagnose it is to get the logic tree for DTC 42 from the shop manual. It will walk you through tests that will help you pin down which component is causing the problem.

 

Bad OPTI in my experience. Had the same code. Car would die, turn on the key and injectors would start clicking, fuel pump would cycle, guages and tach would bounce all over the place. Took apart the OPTI and the inside looked like it had been dunked into saltwater. Corrosion all over the place. Replaced the OPTI and was good to go, all codes cleared. Good luck, I'm placing my money on the OPTI.

 

Bad opti even tho the car starts and runs mint other then in OD at a steady 80-90?

Im gonna trace the wiring again today and *** an extra dround from the head to the body and see what I can find. The car did not have this code before I chaned the harness which was 4 days before. And it hasnt rained or got wet.

Jay

 

I just thought of something I have a VATS1 box spliced into i beleive that white wire ignition control.Im gonna try tuning vats out and disconnecting that to see if it is messing the signal up!

Ill keep posted in a few hours when I get home.

Jay

 

Well it was the VATS1 box as I assumed I went into tuner cat and disabled VATS and took the box off and the car drove fine and didnt pull any codes

opti...pffff lol

Thansk for the help anyways.

Jay