I ran into this problem after cleaning the intake plenum, runners and throttle body as well as doing a EGR delete. I had the car running, did all my calibrations for TPS and it ran fine after that. I came back days later to start it up again and it fired briefly and died, haven't been able to start it since.

The ICM was fried so it got replaced, no change.
The pick-up coil was corroded but tested fine, it got replaced regardless, no change.
Coil has been replaced.
Cap has been cleaned and rotor replaced but this shouldn't have been causing a problem as there is no spark coming from the coil anyways.
Harness between dist. and coil is good.

I am going to take the ICM back to get it re-tested to see if there is something causing them to go bad. Until i can do that i thought i would get a second opinion and see if there is something else I can try. Next stop is the ECM i guess. Any help is greatly appreciated, thanks.

 

I'm pretty sure that the ECM is not gonna keep you from sparking. It controls the spark advance via the module in the distributor, but spark or no spark goes without that.

Make sure you have your 12volts coming to the coil on the fat pink wire when the key is on. Make sure you have a GOOD ground for the coil.

I like to first just hook one spark plug wire to the coil and a new spark plug, and then hold the plug to an intake bolt, just like I used to test spark on old cars when I was younger. That will at least further isolate your problem.

Also make sure that you have 12 volts to the coil DURING cranking. You might have the power cutting off during cranking.

 

As stated, the ECM doesn't have an effect on if there will be spark or not, for the most part.

At cranking, the the ICM doesn't accept input from the ECM to control timing and runs off "base timing", until 400 RPM is reached. At 400 RPM, the ECM sends a 5V signal on the "bypass" wire to take over control of timing. You could have the ECM sitting on the bench and still have spark.

Have you tried a different coil? Coils do go bad from time to time. Have you checked for a signal from the ICM to the coil, have you checked for 12V at the coil and the ICM?

 

Thanks for the replies,

I do have power to the coil in run, I haven't yet checked it during cranking, will do this tomorrow.
I tested my coil and it tests fine, I did try a coil from an S10 that was running and now have a new coil installed.
Correct me if i'm wrong but i'm assuming the signal from the ICM is a pulsed 12V signal that I should be able to read with the DCHz scale on a multi-meter, I'll check this as well.
I had read on another thread when I did a search that the harness that comes from the ECM to the ICM only provides ground and 2 5V signals, don't know if this is true, I figured there would be 12V to the ICM. I'll see what I can find there tomorrow.

Thanks for the help, it always helps to have a new set of eyes look at the issue.

 

When you put a new module in the distributor, don't forget to put a lot of heat paste on the backside before you bolt it down in there. New ones fry quickly without enough paste. Also don't forget that the parts store will check your module for free with their little plug in machine. New chinese stuff can go bad straight out of the box.

When you look at the module, the 12v in would be on the + terminal of the two prong plug.

Your 4 prong plug on the other end of the module is all the ECM interface stuff. The two prong plug is the coil interface.

On your 4 prong plug, the tan/black wire is the bypass and it doesn't matter for testing spark. Its the one you disconnect when you set your base timing with the light.

The white wire is the one that the ECM sends a signal to the module for changing timing while you're on the road.

The purple/white is the high reference to the ECM, the black/red is the low reference to the ECM. These are the inputs that the ECM uses to determine what signal to send back to the module on the white wire.

None of the ECM interface should have anything to do with a no spark condition.

On top of the coil, you have 4 wires. You should have 12v on the one side and the other is the side where you get your tach reference and where the module turns on and off the ground to make the coil spark. The module grounds to the distributor base on its backside with the aforementioned heat paste helping to not melt the module in the process.

You may want to do a quick check for a good ground by grounding the distributor housing and doing your spark check again. If your engine grounds are not so good then the distributor ground becomes poor. Grounding it separately helps eliminate that.

 

So i managed to take another look today.
There is 12v to the coil during cranking and there is 12v leaving the coil on both terminals that go to the ICM. I have attached a diagram of my situation.
The ICM-to-coil harness tests fine for continuity and should not be able to ground out anywhere.
I have a good engine ground and tested ground at the distributor so the ICM should have no trouble grounding out.


The coil did get warm today during testing, perhaps I have a ground somewhere I shouldn't have? I have checked all the fuses I can think of and checked wiring diagrams and everything should be in place to start the engine yet there is still no spark.
I will be able to take the ICM back to have it tested again on tuesday. Whatever happened when it first died must have burned the ICM because replacing that didn't fix the problem. I'm running out of ideas of what the problem could be.

 

Try to clean the harness between the coil and the ICM, those wires should be pink and white. When not running or cranking the engine, both sides of the coil will have 12V on it, with the key on. This is a property of all electrical components. Voltage passes through the component until the opposite polarity is met. So in this case, the 12V ignition will be supplied on the pink wire, pass through the coil to the wire going to the ICM, to provide it with 12V, but also pass through the coil windings and be measured on the "negative" side of the coil. If you were to place a ground on the negative side, this would charge the coil, and would show zero volts at that same terminal. Once that ground was pulled away, the coil would spark. The coil releases the energy, when the ground is taken away from the negative terminal, due to the collapse of the field.

What you need to do is set the DMM to AC volts and place it to the ground side of the coil while cranking, to see a signal from the ICM.

Does the car have a tach? If so does it move when cranking?

 

Thanks six_shooter, that has cleared some things up for me. I have the ICM out now and won't be able to work on the car till tuesday afternoon. By then i'll know if the ICM has been fried again or if it is still good. I'll do the test you talked about and see what it tells me. Thanks every one for your ideas.

 

I got back at it today, still haven't had and success. I see there is another thread that got started recently with a lot of the same symptoms I have been having so I'll follow that one too.

-The ICM tested fine again when I had it in at the auto shop.
-When I tested the signal from the ICM to the coil there was no change, it never grounded out. I would have suspected the pick-up coil but when I had it out I tested it and I was able to read the signal with a multi-meter.
-I was un-able to fire either of the two Camaro coils I have by grounding them manually but was able to get spark out of the S10 coil I was testing with earlier, different operation maybe? All the coils test fine when checked for resistance.
-The 4 wire ECM interface plug has no signal on any wire but as it was said earlier this shouldn't affect anything.

To me it is starting to look like I have a bad module despite it passing the test every time. In the other thread they talk about a wiring diagnostic tree, I have searched for something like that and was un-able to find it, If you know of one let me know. Any ideas are appreciated.

 

Hey, I noticed you're having similar problems to what I had. I also was unable to get spark out of any of my coils (I bought one brand new one, had the one that was already in my car, and one older one laying around). I had gotten continuity from the coil bracket to the straps so I assumed the ground was good. But I replaced the bolts and straps anyways, and it fixed it.

So, if you haven't replaced your ignition coil straps, do that. I can't guarantee a fix, but it worked for me, after replacing the pickup coil, distributor cap and rotor, ignition coil, and spark plugs.

 

Well I figured it out. Thanks for the reply Stalker7D7, it actually turned out to be a similar problem. The coil had a good ground to the body but the black and white wire leaving the coil on the power side, I believe it is the tach signal, was grounded out. It had gotten pinched in the bell housing after a recent clutch job. So if you're finding yourself here after a search the lesson here is to suspect something simple first. I was misled by a failed ignition module to believe it was something more complicated but as it turned out it was just a bad ground. Thanks to everyone who presented solutions, at least this thread will serve as a good base for someone who is having a similar problem.

 

Solution logged in. Thanks for reporting back and not giving up!