Help needed: Code 42 - Electronic Spark Control Error

[QB93Z]

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?

[XfireZ51]

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.

[Pete]

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

[GOLDCYLON]

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?


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

[QB93Z]

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

[oricale]

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!!!!

[GOLDCYLON]

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

[tomtom72]

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

[oricale]

PM sent!....

[tomtom72]

PM answered!:cheers:

Tom

[tomtom72]

Demps....check your PM's.:thumbsup:

[oricale]

Got em'! tom!!:cheers:

TOM: Did you expereince the same symptoms/...hesitation and lack of power??How about idle fluctuation?...

IF NOT,.. would it be possible that the fluctuation is due to the little check valve under the plenum is either failing or backwards?......AND what is the check valve actually used for IF I have eliminated all the secondaries and smog/air crap!!

[tomtom72]

:osorry, I was e-mailing my Boss.:o

Check valve is to keep vacuum in the tank as a reserve & source at wot..I think. If it was in backwards then maybe it's a big vacuum leak. Without secondaries it is redundant I think???

When I had my mistake & bent the pin the symptoms were as follows:
SES light lite always; batch fire on injectors; no secondary function ( I still have my system OE) no balls, not that it mattered. Also the entire ignition system uses only the ESC box which is a limp home feature so you don't get stuck.

:o I'm no expert ( I'm a master of understatement though! ) on LT5's sans secondaries. To me if it's generally sputtering, like loading up? Then the fueling and or the timing is bad? Or the injectors are dumping too much fuel? Or there could be a vacuum leak the size of the grand canyon? That's JMHO.

I'll hold off on the DIS box if you like. Use my e-mail addy posted to advise me of what you want to do going forward, okay?

:cheers:
Tom

[oricale]

Tom...NO..proceed, these are the same issues I have,..did you have a code 42 or????...here are my symptoms:

1. Fluctuation at idle either after 4 min at idle or after reving up...800-1100
2. 1st gear has no balls,
3. hesitation (although slight)
4. a back fire every no and again
5. NO BALLS!(cant spin tires, doesnt "really" put you back in the seat!
6. 4 gear..stomp on it and I got smoke at the pipes(not sure how much)
7. on high rev down to stop, makes a wierd sputter ("release" rythm like the idle)

ALSO! who here can work on a throttle body or can tell me how I can fix a throttle body that I have to tap to get the throttle down??

[tomtom72]

Okay, I'll try to get to the Post Office at lunch. Not looking too good as a major redecoration project at my job is going sideways, and fast!

Yes I had a 42. It was the bent pin preventing proper communication(?) or preventing the ECM from knowing that the DIS box was 'there & willing to work'? I'm not sure which, but the result was the ESC box and the starting protocols in the ECM took over management of the ignition system. The result is a somewhat sick LT5 with useless extra fuel injectors!:sign10:

:cheers:
Tom

[oricale]

Holy S^&%t that might be the whole issue!!!

[tomtom72]

Demps, you have a PM. The long & the short is the USPS says tomorrow you will have mail!:mrgreen:

:cheers:
Tom

[tomtom72]

Yo Demps! Please tell me that the DIS arrived today? :pray

[oricale]

SOLVED!!!!...:p:dancing It was a damn pin!!!just like tom had....I couldnt see it till I pulled the ignition module out at compared it to one Tom sent me(you rock Tom!!) the pin was buried!!!!..So no codes, idle seems solid... ....NOW ANOTHER PROBLEM!!!!!!(SEE NEW POST!!!" Almost BG bound-Need help AGAIN"

Again thanks for the info and assistance!!!!:proud:

[tomtom72]

Yo Demps, who is C. Perry???? They signed for my DIS box yesterday at 11:45 AM. Do you have my DIS? Speak to me please.

:cheers:
Tom

[oricale]

Tom...You are good my brother..C.perry is the front desk person for my condo!:):cheers:

I took it out of the wrapping found the problem and wrapped it right back up!.....ha!

I can bring it with me to BG or mail it right back to you!


Again Tom, you rock!

Thank you to all of you who continue to bare with me saving the #517