Terrible Juan

My car is running poorly. It idles pretty good and even drives OK until you roll into the gas. If you try to put any power to the wheels, it starts stuttering, almost like the car is running out of gas. I checked the codes and I pulled a code 42, which the FSM says is related to the Ignition Control circuit.

In the FSM, it says that either I have a bad ground somewhere, or that the ignition coil, ignition coil module, or ECM is faulty.

Well, I've never heard of an ignition coil module. From the picture in the FMS, it is directly mounted to the coil but it looks like there is a seperate harness for it which I've never noticed.

My question is... are the coil and the coil module all one piece? In other words, if I buy a new coil, will it come with a coil module attached? I was unable to find a "coil module" when I searched for parts on Autozone, Kragen, and Napa's website.

Any help would be appreciated.

This is for a 93 LT1 Auto, by the way!

Tom Piper

If I remember correctly, before I removed it and installed a Delteq, the coil and coil module were on the same heatsink assembly on front of the right-side head.
The coil module can be removed by taking out the screws and the coil can be removed by taking out the rivets -- the new coils I've seen come with screws to replace the rivets.

The coil has two (piggy backed) connectors (they changed this to one connector in '96) on it and the module has its own connector.

Even though the coil modules from '92 to '96 all use the same connector, these modules for most years (there are a few that are the same) are matched to the coil -- a good example is the '96 coil has a lower primary impedence for faster coil saturation (more dwell time) to allow the LT4 to rev to a higher rpm, so the '96 coil should be matched to a '96 coil module for it to work properly.

Tom Piper

Terrible Juan

According to the FSM, the coil and the coil module are two seperate entities, so I'm guessing the coil module is purchased separately from the coil? If so, is this coil module going to be a dealer-only item? All the pictures I've seen from the parts store websites show a picture the coil with just the two piggybacked connectors are no connector for the coil module.

I'm very confused.

onedef92

I think that's one of the misprints in the FSM. That coil module is your Ignition Control Module (ICM).

Check it out in this pic below and its location.

The ICM is the "brain" of the ignition system. It controls the ignition timing and strength, as directed by the ECM or main computer.

Bill Hetzel

See Def's pic, it's easy to replace, just don't drop the little screws.
The module comes with thermal transfer grease for the back where it sits on the heatsink. The grease on yours will be gone.
I replaced one on my 92 chasing a problem with the opti. The grease was gone but it still worked fine, now I have a spare.
Some guys have had good luck getting them tested at Autozone and some Autozone's had no clue or no connector. I'd try to get it tested because the GM is $165. I put on an AC-Delco for $110.

Darkgh0st

I replaced mine a few months ago.

Great Writeup by RickReeves1 here- http://forums.corvetteforum.com/show...highlight=coil

I suck at mechanic stuff but I was able to handle this project. The power steering reservoir bracket was a real b1tch getting back together.

(My problem turned out to be the opti)

RED92LT1

I had the exact problem on my 92 except it completely failed before I replaced it. I got one at Advance Auto for $84 and it works fine. However, I also ordered a Borg Warner which I will be swapping for the Advance Auto unit ... I'll be keeping the Advance Auto unit as a spare.

And make sure you use the grease on the back of the new unit. It transfers the heat away from the module and prolongs the life of the module. Interestingly my old module did not have much heat sink compound (Silicone grease) left. Most likely why it failed.

For any modules still working ... probably a good idea to remove your ignition control module and recoat with heat sink compound (Radio Shack) or silicon grease before it fails.


Brian

Terrible Juan

Thanks so much guys. The FSM says the first step to diagnosing the error code is to reset the codes (disconnect the battery for 15 min) and crank the car for 15 seconds to see if it comes back. Well, it didn't. In fact, it fixed the problem. I did disconnect some of the connections under the hood but I'm not sure if that fixed it.

I'm convinced that my ECU is bad. This is the third time I've had a major problem go away just from resetting the codes.

pcolt94

Ok, lets start from the top. I believe on a 93, a code 42 is EST (Knock sensor) Grounded. The code may or may not mean anything since the engine was running bad and the knock sensors could have produced the code. If it was grounded or shorted the code would probably return.

I don’t believe the ICM is a device that is monitored by the ECM or CCU hence it is not monitored and would not throw a code. Where did the FSM say this?

I think you might need to start with a fuel pressure check make sure it is in the proper range for idling, and under some load at higher RPM. If bad, think filter or pump.

If the fuel pressure seems to be OK, you might just keep an open mind for a bad opti. There are a wide variety of symptoms that can make the car run real bad under load. Most likely there will be no code associated with this.

The other common problem is the ECM. All kinds of run ability problems. But that would be lower on the list at this time since many sensors and devices connect to it for sampling of operating parameters. They should be checked first.

Terrible Juan

Code 42 is the ignition module (grounded). Page 6E3-A-74 of the FSM.

I have a new fuel filter but it is possible that the fuel pump is bad. I checked the fuel pressure with the FPR unplugged and it was at 42 which the correct PSI. I didn't do a load test. I am going to drive it today and see how it does.

pcolt94

Checked another source and it did relate to an ignition problem. Always go with the FSM so OK. If the FSM is referring to the ICM, ignition control module, then lets talk about it. Only you can look in the book and see what the electrical tie in is, and what point is being looked at to produce the error code.

Basically the ICM is an amplifier that takes a 5 volt pulse from the ECM and amplifiers it to about 65 volts and drives the coil. If you have weak spark under load the coil or ICM could cause this. Since more ICMs go bad rather than coils, and the error code relates to the ICM, zero in on it for now. What ever is sensed by the PCM can’t be that bad or the engine would probably not run. Autozone, I have heard can check the ICM. But even if they can, the problem might not even show up with these symptoms. Substitution is really the best way to go. Installation of this unit is very quick and easy.

The coil is cheep and easy to change and can even be hooked up temporally with out removing the original coil. Just in case you wanted to try one. Just electrical plug it in and let it hang.

Anything is possible with electronics and don’t know if a bad pulse from the ECM could produce the error code. Error codes are only hints and starting points.

shadowman1

CIRCUIT DESCRIPTION
The ignition system supplies two reference signals to the ECM. A "high resolution" signal provides 360 pulses/crankshaft revolution, and a "low resolution" signal provides 4 pulses/crankshaft revolution. The sensors are in the distributor, which is driven off the front of the camshaft. Reference signals toggle between 0 and 5 volts as the camshaft turns. The ECM provides a 5 volt reference to each of the signal lines, and the signals are produced by the sensors alternately opening and closing the circuits to ground. The ECM uses these signals to determine ignition spark timing for each individual cylinder. Once the ECM calculates the ignition timing, a timing signal is sent to the coil driver, on the EST circuit, and the coil driver triggers the ignition coil. The EST signal changes from a "low" state (approx. 0.5 volt), to a "high" state (approx. 4.5 volts.)

Code 42 will set if the engine is cranking or running at less than 3,000 rpm, and the ECM detects voltage less than 0.5 volt on circuit 423 (EST circuit.)



NOTE: If Code 42 is set, the ECM will disable the fuel injectors to prevent flooding.
A Code 42 will set if the high and low resolution signal circuits are shorted to each other. Before replacing any components, make sure these circuits have continuity between the distributor and ECM, and are not shorted together.

pcolt94

Most of this in formation sounds OK and know it came out of the book which is fine, but I have a few questions and comments.

What I gather from the information is if the 5 volt ECM drive pulse is below a certain minimum voltage the ECM will disable the injectors. But if it was indeed that low, the engine would not even start.

If you loose the high res pulse the engine will still run. Its mainly used for timing. The Low res pulse is used to let the ECM know where the engine is and used to determine which cylinder to fire and injector to use. If you lost this pulse, was shorted or not useable in some way, the engine would not even run.

Now, if the high res pulse was not there and timing was affected, then I could see a reduction in power.

If the code 42 was truly set and it disabled the fuel injectors, I would think it would be total shutdown and not partial. He has never stated that the engine completely quit, but only lost power or just would not accelerate correctly. Seemed like it was still running and getting fuel, as I understand the information provided.

Agree - Disagree

shadowman1

If the pulse is off the shutdown of the injectors could be momentary. I was just addressing the code. He will need to do a step by step diagnostic. A loose connection will throw off the signal when you are dealing with 5 volt reference signals. Connections need to be secure.

Terrible Juan

All of my connections are secure. I double checked the two coil connections and the ICM connection. A code 42 was set. I have it written down from when it popped up during my code scan.

I drove the car to work today and it was fine until I got near my work. It started hesitating again. I checked the codes when I arrived at work and there was no code present. I checked the codes when I got home from work and there was no code present.

It is still giving me the same symptoms as before. The car starts up and idles slightly rough but ALMOST normally. There is a small amount of hesitation on takeoff and a small lack of power if I drive it very easy. When I give it a lot of throttle, the car starts hesitating as if I am running out of gas.

This seems to be a timing advance issue because if I manually select the gears, I can accelerate quickly and redline the motor without getting any of that weird hesitation. If I push the gas pedal past a certain point (about 1/3 to 1/2 way down) it will hesitate no matter what gear or RPM I'm in.

ICM seems to be the culprit?

pcolt94

Of all the things I read about for ICMs, is that they just die, causes no spark a lot of the time. The ICM is just an amplifier just passing a square wave pulse and as RPM increases, so does the frequency. The ICM knows nothing about anything going on in the engine except that pulse from the ECM. Chances of it being frequency dependent are possible but I feel remote.

Now for the other side of the coin. Going out on a limb on this one.

OPTI – You have many of the classic symptoms of a bad opti. Many of your symptoms were very much like mine. I had no codes, checked EVERYTHING and could find nothing wrong. Even changed the coil just on that chance. Then I changed the opti and like magic, I was fixed.

Was tough the first time especially the removal of the balancer. The rest of it is just parts and bolts. Set 2 days aside to do it. You will get more help and information on the Forum than you will know what to do with.

But Ha,,,,, this is just a suggestion.
Best of luck

Terrible Juan

I'm not afraid of the labor involved with the Opti...

... it's the price involved.

I would like to hear from other people about this ignition module issue before I set aside the cash for an Opti.

Is is possible for my cap and rotor to be original and carbonized to hell and causing arcing? It doesn't make sense why a failing Opti would cause the car to run funny when put under a large load... does it?

corvette1989bham

Replace water pump and opti- bite the bullet - live life -be happy!

Darkgh0st

Opti problems appear with many many different symptoms. I just got over an opti problem myself that took me 1 year to finally find.

The general rule is to rule out the basic and least expensive (parts and labor) first.
This should be your route for troubleshooting an ignition related problem:

#1- Plugs and wires: Very basic. With my problem, I found some wires arching and replaced both plugs and wires to cover all bases. Look at your wires in the dark (pitch black after your eyes adjust) and see if you can find small blue lighting. Search for more info

#2- Coil & ICM- I was able to do both of them myself. The coil was a cheap $30 and I bought the ICM from the dealer for $90. I was able to do the work myself. Reference the thread I posted for more info on replacing this.
-------
IF your problem still exists after steps 1+2 then you need to go to step 3 the OPTI. I couldnt find a shop that had the ability to diagnose my opti as being bad, but even if I did than it would have taken several hours to pinpoint.
--------

#3- Opti. I bought an MSD opti for $450 shipped and replaced the waterpump at the same time. Waterpump was $200 at summit racing. The only reason I did the waterpump is that Ive read many times that you need to do that when doing the opti since it will be apart anyways. The labor was $400. Total cost for the opti and waterpump replacement was $1000 parts and labor. (BTW, the shop told me that my waterpump was leaking and that's what slowly killed my opti)

Yes, it sucked. Yes it was alot of money that I didnt want to spend but it fixed my problem and now my vette runs like new.

I can't tell you if your problem is ignition related or not, but if it is then I recommend following those steps to fix the problem. You might luck out and find something simple, or you might need to replace the opti.

Good luck

Darkgh0st

Yes 100%
Yes, your opti will cause your engine to be:

Completely Dead - - - - - - - - - - - - - Running Like Sh..t
and anywhere in between ^