Hi all, I want to bounce this off you all to see if anyone has any idea what's going on.

Bogus has been helping as well.

93 LT1 Auto. Had a roughness and appearance of a mis-fire. Code show DTC 41.

When the engine reach ops temp 204 or so, it would die, let it cool down 20 degrees it would start back up until it got to temp again.

Traced it down to the ignition coil module. (Coil is new too). Replaced with a new GM module. It won't start just cranks. Probed all wires to coil, ground and ECM all good continuity.

Plugged in the old module it starts at first touch of the starter. Ordered another new module installed it this morning same thing. It cranks but won't fire. Plugged the old module in it fires.

Any ideas? I'm at maximum frustration on this.

I had Chris verify the pn on the module and it is correct.

 

Try a GM spark control module.

 

That is different from a AC/Delco Ignition Control Module?

This is my second one in two days. PN 10483131 if my memory is correct.

I took both the old and new module to NAPA and had them tested. Both test ok.

What in the heck is going on????????

 

WTF Man that sucks. Only thought I can come up with is corrosion in your connections.A little electrical cleaner mabey? Or mabey a connector is just not making good contact.Good Luck

I assume you checked for spark and have none right?

 

Since the new module won't fire the engine, I re-installed the old module. It fires right up. I let it come up to temp, although it was just slightly rough, I let it come up to 230 fan kicked on brought it back to 219, did this for about 20 minutes could not duplicate. So I took a break and ate some dinner.

I took it out for a test drive around and around my subdivision (didn't want to go to far) and finally it started to misbehave. It had a roughness to the idle at first, but after a number of time up and down the street the first symptom was the tach started jumping. I quickly headed back to the house, while heading back down my street the tach started jumping wildly. Pulled into the garage let it idle for a minute the temp was about 212, and I rev'd it a couple times the tach was going from 0-redline and then it started stumbling I brought it up to about 1000 rpms for a few seconds then it started cutting out and died. I restarted it, it started right up for about 2 seconds and died. I repeated this a couple of times and each of those it would just start and die.

I shut it down and pulled codes. BTW I never got an SES lamp or anything else beside what I described above.

Codes were clear before I started all this too. The codes for A-G were: 1.0 C12, 4.0 H41, and 9.0 ---
Then for A-B a 1-2 for the start of the sequence followed by a 4-1 then a 1-2 indicating the end.

The more I dig into to this the more I'm getting confused.

The way I'm interpreting this is the 4.0 display is an ECM DTC 41 followed by the ECM (A-B) a 41. Which is an Ignition Control Circuit (open or short circuit).

I just don't understand what is going on.

Yes when its running it seems 95% fine. During all my testing I did check continuity on all wires coming from the ECM, to ground, and the two going to the coil.

There has to be an answer some where as to what is going on.

I really need help. I'm renting a car right now as this is my only car.

 

It sure sounds like something is opening or shorting when it heats up. Code 41 came up on your old one right not the new one? I know you said you checked continuity but did you check inside each plug and look at the contacts on both ends. One of them may have loosened up with age and may not make good contact with the other one.All I can think of right now but it has to be connection related if they check out at the store.

 

Yes the plug is the female end. And it was check thoroughly while probing for continuity. I check the white wire from the control module connector back to the ECM, the black to ground, the white and pink/black to the coil connector all is good.

The new module will not fire the engine. Neither of those new modules would fire the engine. Only the old one will fire then engine.

 

Do you get the code 41 with the new ones or the old one? I have heard of these modules being bad but what are the odds that 2 would be?Besides they check out at NAPA right? What about the connections on the module side by side with your old one are they the same thickness and size?Man I can feel your frustration but it has to be a connection or bad module(2?)

 

The DTC 41 comes with the old one. The engine will not fire with either of the new ones. It just cranks. Yes the folks at NAPA tested them and they both test fine.

The modules are identical.

I don't know what to do next. Any normal person would have dumped this car long ago considering the amount of money I've had to put into it. The situation is now critical and today I'm going to evaluate the very possibility of taking a huge loss and dumping it, ending my Corvette ownership. I never thought I'd give this car up but this is at a point where it may be the end of the line.

 

Hey, it's Brian. Suffering similar problem, but not the same I don't think. I feel your pain. I've been swapping out parts and the car is currently down waiting for the new MSD optispark to come in. So, I'm redoing the entire engine in anticipation. You've got a couple choices. You and I are pretty smart and we've done everything we can do. Send it to the dealership and you'll get it back running with an answer of what was wrong. No shame in that unless your a dealer tech. Probably a $1000 bucks, but who knows. Taking a loss of more than a $1000 would be silly then.

There's always aftermarket injection as well. Cranktrigger maybe, but the block will still accept a distributor if you want and there's a guy that will modify the manifold for you.

 

The coils from '92 to '95 have the same connectors and look the same, but there were some differences by year. The '96 coil has a completely different connector.
The ignition control modules from '92 to '96 have the same connectors and look the same, but once again, they are different by some years.

There is a big difference in the '96 coil and ignition module from previous years and they should always be used in a set -- that is, you could plug a '96 ignition module into a '92 system, but you should not do it.

The point of all this is:
Are you sure you have the correct ignition module and coil combination?
From '92 to '95 the look identical, but you should not mix them.



Tom Piper

 

I know 92/23 had the same module, 94/95/96 uses a common module but different than the 92/93 model years, coils will all work between 92 and 95. Coils in 96 had a single 4 pin connector versus the dual connector of the preceeding years.

 

I'll check with Chris @ Superior today to find out what coil I got from him a month ago. The ignition control module has a four pin connector. P/N is 10483131 if I remember correctly. I called Chris, the local Chevy place, and spoke to NAPA and all three confirmed that this is the correct ignition control module for a 93.

I really appreciate all of your thoughts on this matter. I know you all have such a wealth of knowledge.

Brian, I appreciate the thought, but I don't have that kind of money to make major modifications. I just want my stock engine to run. When I initially called the dealer that I usually use, the service advisor kept saying its the opti spark. I don't agree with that. In fact they replaced the water pump and opti not but less than 3 yrs ago to the tune of over $1300. And of course they don't warranty that. I'm very concerned about taking to the dealer when they have preconceived notions without listening to the issues.

When it is cold, with the old control module, it fires right up at first touch of the starter. Plug the new on in, and all it does is crank. With the old one in it has a very pronounced roughness to the engine up through about 1500 rpm. If you rev' it, it seems normal. Once it comes up to temp and you run it just a bit then all hell breaks loose, the tach goes wacky, it starts stumbling and dies.

I'm just sick over this. I know I'll get reamed if I attempt to trade it in especially with it not running. Its sad because I have invested so much money to restore it to practically new condition. At $60. a day I can't keep renting a car either. Something has to happen today or tomorrow. I can't afford to be reamed be the dealer for $1000's of dollars either.

 

My gut-feeling is you have a connector problem where it is making poor contact in the old ignition module when it runs and no contact in the new one when it doesn't run.


Tom Piper

 

Hey Tom, I just spoke to Chris at Superior and he confirmed the coil part is for my 93, I got a new one from him back end of May. He also confirmed that the control module is the only one for 92-96.

I checked the continuity from each pin of the connecctor, white wire to ECM, Black to ground, Pink/black and white to coil. All showed good continuity.

I'm thinking about ordering a new ECM computer and another control module as my last resort. I asked about the wire harness but that is not available. How would one repair a marginal connector like that in this case?

 

I have a hard time believing the '96 module is the same as a '92, but I'm not a parts man.
The '96 coil has a much lower primary resistance -- a hotter coil.
A hotter coil logically would need a different driver.


The easiest way would be to cut the connector from a donor vehicle and splice it on yours.

Tom Piper

 

If you know someone with an electronics background and a dual-trace oscilloscope, with the ignition module connected, have them put the input to the ignition module (which is also the output of the ECM) on one trace and the output of the ignition module (which is also the input to the primary of the ignition coil) on the other and check the signals.
This does away with all the guess work.


Tom Piper

 

Jetjockey and I have been PM'ing on this for several days now...

and we are no closer to getting it running.

The heat soak led me to the Coil Driver/Ignition Module... it would heat up and die. Then, when passed through the various test light troubleshooting instructions for the C41, the module made sense.

It could also be the coil... once it heats up, it loses resistance on the primary side, and all hell breaks loose.

One item from a PM, every so often, the AC would go from cold to hot, the ASR and ABS lights would come on and a CCM C41 would appear. This is telling me that something is wrong with the serial data line somewhere between the CCM and the EBCM and the AC programmer.

However, if the CCM dies, even whilst driving, the car will continue to run just fine! It's when you go to restart that the problems ensue.

Another thought - there have been some posts regarding AC voltage leaking from the alternator... that might be worth checking into.

 

Well I do work with EE's and I believe we have those systems at work but I couldn't not bring it or them back to the house. We develop controllers and such where I work.

I'm not sure I completely understand what your saying though. Nevertheless, I suppose this is something the dealer woudl do I guess.

 

I replaced the alternator with a Delco reman about 9 months ago or so. My previous one was making a lot of noise and I wanted to replace it before it died on me. Sounded like bearings when you put a screwdriver to it and to your ear. After I replaced it, it was very quiet.