Missing injector and spark pulses

[TopNotch]

It seems that the ICM is overheating.

What kind of heat sink compound did you use?

[GTRS Fiero]

Wells.

[The Art Doctor]

Often wondered why the caps are not ventilated.  Some sort of hole or holes with a screen or foam filter.  Could even have a small fan in there.

Do you have an IR temperature gun?  very useful for these types of issues.

[Fierofool]

Larry, the Fiero V6 distributor does have 2 screened vents in the base plate.  But GTRS is running a 7730 with the coil pack.  The ICM is mounted underneath the coil pack. 

GTRS, ignition coils can work well when cold, then break down as they warm up.  Of course, the same holds true for the ICM, too.  It does seem to be one of those two items, though, unless it only happens as soon as the ECM goes into closed loop. 

[GTRS Fiero]

The coils have also been replaced.  No change.

[Wreck It Ralph]

I solved some and created others when adding my shield.

That's a bit vague.

Well I made a shield and replaced some other stuff. Ends up I got a bad crank sensor. But I still have the same problem. I haven’t pulled the new scanner out of the box yet. So only time will tell.

[GTRS Fiero]

I'm going to replace the coils again, and see what happens.  I don't know how to test the coils separately from the ICM.

[GTRS Fiero]

Well I made a shield and replaced some other stuff. Ends up I got a bad crank sensor. But I still have the same problem. I haven’t pulled the new scanner out of the box yet. So only time will tell.

The same problem you had, or the same problem I have.

[Wreck It Ralph]

Same problem I had but similar to you but it’s a spark misfire instead of injector issue.

[GTRS Fiero]

Here are the facts:
1. The engine appears to run fine when cold, for about 15 minutes.
2. The ICM and coild have been replaced.
3. The heat shield is in place, but the symptoms remain when removed.
4. When the issue is hapoening, the signal from the crank position sensor to the ICM seems to be good.
5. When the missing is happening, the signal from the ICM to the ECU seems to be bad.

Here are the symptoms:
1. The engine will be running fine, then start missing, after about 15 minutes of running.
2.  Idling, city driving, highway driving all appear to be the same.
3.  The only constant in this occurring is time.
4.  If, after the problem occurs, the vehicle sits for a few minutes, the engine will again run fine.  The longer it sits, the longer it will again run fine, up to about 15 minutes.
5.  When the missing occurs, if I try to keep driving, the engine will die.  On the other hand, if I just let it idle, it idles fine.
6.  When it misses, the tach jumps all over the place.
7.  If I stop the vehicle, place it in Park, and gently blip the throttle while idling, the tach may show max RPM, or 0 RPM.

[GTRS Fiero]

Once an ICM has failed once, is it bad?  A new ICM behaved exactly the same.

[GTRS Fiero]

Same problem I had but similar to you but it’s a spark misfire instead of injector issue.

My injectors weren't firing, because there was no signal from the ICM to the ECU.

[GTRS Fiero]

I replaced the coils and ICM with an old set, and the car ran for about 40 minutes before stumbling.  I shut it off, but when I tried to start it about 5 minutes later, the engine did not want to start.  I let it set for another 3 minutes or so, and it started right up.

To my knowledge, the crank position sensor gets its input mechanically, but provides electrical output.  The signal from the crank position sensor to the ICM is good, but from the ICM to the ECU is eventually garbage.

For the last few years, i've had an exhaust leak at the EGR, right by the ICM.  Sometimes, I could drive for several hundred miles, with no issues, but then the gasket would blow again.  No issues with stumbling, though.  There are no current exhaust leaks that I can detect.  I see no reason to believe that it is suddenly hotter in this area.

The issues seemed to start right after the heat shield was installed.  I've tried with and without the heat shield.  The stumbling still occurs.

[TopNotch]

The crank position sensor uses the "Hall effect" to produce electrical pulses. In other words, the crank position sensor is basically a magnet with a coil of wire wrapped around it. It is positioned close to a wheel on the crankshaft that has notches in it. Each time a notch passes by the sensor as the crank rotates, it disturbs the field of the magnet, which causes a current to be generated in the coil of wire.
The crank position sensor is a simple device, but it can go bad. If you haven't, try replacing it.

[GTRS Fiero]

Well, on the 6th one.  The first 2 were just bad.  Then there were several that had issues.  The previous one had oil leaking up through it.

I think the problem is the ICM itself is overheating.  I relocated it inside the trunk, with a ground to the engine.  Same issue.  I suspect it's much cooler in the trunk than by the crossover pipe.  In any case, the exhaust shouldn't have been causing issues with excessive heat in the trunk.

Is there anything that could happen to cause the ICM to generate more heat?