Help needed: Code 42 - Electronic Spark Control Error
 

We are trouble shooting a Code 42 - Electronic Spark Control Error on a 1991 ZR-1 that was rebuilt after a cam chain failure.

I don't know if this problem is related to an idle speed control problem that we are also trouble shooting. The symptom of that are that the idle rpm oscillates from ~950 to ~1100 with about a 10 second period. During the oscillations, spark advance measured by a Tech 1 is also oscillating.

The Service Manual indicates that Code 42 signifies that the ECM is not seeing the correct voltage on the EST signal from the Ignition Module. After working through the trouble shooting flow chart, the problem may be a failed Ignition Module. Based on how rare IM failures are, I am looking for suggestions of other things to look at. We did verify circuit continuity and connector condition which are other possible causes of Code 42.

The Code 42 can be cleared by the Tech 1, but is set again as soon as the engine starts.

Has anyone had experience with Code 42?

Re: Help needed: Code 42 - Electronic Spark Control Error
 

Jim,

Code 42 us pretty universal in GM world having to do w ignition module. I guess you swap out modules and see what happens. On L98 motors that was pretty cheap to do.

Re: Help needed: Code 42 - Electronic Spark Control Error
 

If you put a scanner on it,check to see if it's pulling timing/knock retard.

Check knock sensor wire make sure it's not melted to the header or touching ground and or make sure it's connected to the knock sensor, check knock sensor make sure it's not too tight or bad knock sensor.

Pete

Re: Help needed: Code 42 - Electronic Spark Control Error
 

With the plenum pull any possibility a pin was bent when connecting to the ignition module on the underside of the plenum? Also Id check the harness to the same module for roaching. GC

Re: Help needed: Code 42 - Electronic Spark Control Error
 

Thanks for all the responses. There was no knock retard. We checked all the pins and connectors. I now suspect that it may be a ground problem and we will look into that possibility.

Jim

Re: Help needed: Code 42 - Electronic Spark Control Error
 

I went ahead and replace the knock sensor and checked the wiring to it...no change
What troubles me the most. Is the lack of power..ALSO.... When I get on it with LOW RPMs I am seeing smoke...all this leads me to believe this is a timing issue..but I am at a loss becuase I have checked everything I know of....I still have the fluctuating idle and code 42 as well!....HELP!!!!

Re: Help needed: Code 42 - Electronic Spark Control Error
 

Anybody as Mark or Corey ? Anybody have an ignition module to loan to test? I do not

Re: Help needed: Code 42 - Electronic Spark Control Error
 

I have a spare DIS box. I'll separate it from my spare plenum and box it up for shipping. Oh, I forgot this...I can lend it to you .:o

I had this happen to me...this is a fwiw btw:o....when I was not paying attention and installed the DIS main harness plug, the one with a billion wires in it, upside down. I bent a pin, just one pin, and I couldn't see it using my mirror either. Had to repull the plenum to discover what I had done.:o

:cheers:
Tom

thomastom72@aol.com

Re: Help needed: Code 42 - Electronic Spark Control Error
 

PM sent!....

Re: Help needed: Code 42 - Electronic Spark Control Error
 

PM answered!:cheers:

Tom