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  • December 11, 2019, 09:59:16 AM

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Author Topic: Broken down!! Ignition module or??  (Read 706 times)

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Offline Mac

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Broken down!! Ignition module or??
« on: November 21, 2019, 10:03:29 PM »
Was driving to work today, and about halfway there, (point of no return, I guess  ;)), it started sputtering and faltering and
stalled out a bunch of times.....

I limped it to work by popping it into neutral many times, driving with two feet trying to keep the revs up...
Had to restart it a bunch of times while coasting...
Got stuck about 4 blocks from work where it would not restart!  A few minutes later it fired and up and I sputterly managed
to get there!!
I basically coasted it into my parking spot at work when it stalled for the last time...

Every time it happened the tach would drop right to zero...   Even though it was still sputtering and surging...

Classic signs of a failing ignition module right??

At around 11am, I went out to see if it would start, and it fired up and purred like a kitten!!!
For about one minute, then died like I'd turned the key off!!

Waited a few minutes...  Tried again...   Same thing!!   Ran about one minute and then shut off!

Totally classic failing ICM right??

Well!!  I've always carried a spare just in case of this sort of thing!!!   Perfect!!
After work, I swapped out the ICM for my spare, and it fired right up!!
Let it run for about 15 minutes in the parking lot and it idled like a dream the whole time!
Locked up the shop, got in the car, texted my girlfriend that the car was fixed, and that I
was on my way to her place!!

The second I hit "send" the car died just like I'd turned it off!
Would not restart...  Got a couple of hiccuppy sputters, and that's it!!

So!!!   What do you think??   If not ICM, what else would cause these symptoms??

I should mention that the spare ICM I installed was an original AMC part that would be about
37 years old now....   And I honestly don't remember where or how I obtained it!!
Pretty sure I wouldn't have thrown an unknown module in the trunk as a spare if I didn't know
for SURE that it was functional, but it was so long ago, I really can't remember!!
I guess there's a chance it's faulty too!!

I'm going to order a new replacement, but I'm wondering if anything else might have similar
symptoms??   Ignition coil maybe???
Haven't had a chance yet to peruse the TSM....

Oh...  I maybe should mention, that it's the yellow ICM with 3 connectors...
1982 only, I seem to recall....
The computer has been bypassed...  No feedback carb...
Large distributor cap conversion...
Original style coil and connector...


Offline amcfool1

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Re: Broken down!! Ignition module or??
« Reply #1 on: November 21, 2019, 11:41:12 PM »
Coil maybe?

Offline mudkicker715

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Re: Broken down!! Ignition module or??
« Reply #2 on: November 22, 2019, 02:43:49 AM »
This does not scream icm.

Manitowoc WI

Offline Mac

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Re: Broken down!! Ignition module or??
« Reply #3 on: November 22, 2019, 07:14:06 PM »
What does it scream??   ;)

It ran one minute again this morning....
Had it towed home after work...   It ran less than a minute up the driveway and
died halfway into the garage...

Going to be probably mid-week before I get a new ICM...
But in the meantime, I'll check all the ignition circuit wiring and connections, and
I think I have a new Flamethrower coil around somewhere that I can swap in to
see what happens!

What really sucks is, that this is my daily driver!!  :(

Offline Draekon

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Re: Broken down!! Ignition module or??
« Reply #4 on: November 24, 2019, 09:53:21 AM »
The tach dropping to 0 does sound like the coil or ICM is failing.

However, I've had the rest of the symptoms you describe occur when crap in my gas tank got sucked up and caused my fuel pump to start to fail. I can't explain why letting it sit would help, but it did. Replacing the pump and installing the prefilter fixed my problems

Offline Mac

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Re: Broken down!! Ignition module or??
« Reply #5 on: November 24, 2019, 07:30:48 PM »
I've had your symptoms too, way back when I first got the car!!

The fuel pickup sock would get clogged up, and letting it sit for awhile would allow the crud to settle back
to the bottom of the tank...
Solved that by dropping the tank, cleaning it out as best I could, removing the disintegrating sock strainer
and installing a prefilter like you did!
Used a clear filter so that I could keep an eye on it, and I went through about 5 filters in the first year
before it started to stay clear!!

In this case, though...   The prefilter is still clean and full of fuel...
So I'm ruling out fuel pump as it doesn't even sputter like its running out of fuel, it just dies instantly like
it was turned off!!

Small update:

I managed to find a brand new ICM in my parts pile that I bought in 2011 (believe it or not!) when
Rock Auto had a wholesaler clearance going on!!  I'd completely forgotten!!!

Before I installed that one, I tried to start the car, and got nothing...
Installed the new one, and it fired right up!!

I was so excited!!  For about 4 minutes!!  ::)   Died again...
Pulled a plug wire, checked for spark...   Nothing....

SO....  The ICM is no longer my main suspect....
Now I'm thinking coil...   OR...   The pickup coil in the distributor??

I recall years ago having an issue with a pickup coil and it was huge pain to diagnose!! 
But replacing it solved everything!!

The TSM mentions a diagnostic procedure for the pickup coil, but I'll be darned if I can
actually find the procedure in the book!!

Doing a search here found a mention of doing the pickup diagnostic, but not actually
how to do it!!
Anyone done it???

Offline MIPS

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Re: Broken down!! Ignition module or??
« Reply #6 on: November 28, 2019, 01:06:29 AM »
If I recall, the vehicle's TACH is generated from the ICM, which derives it from the distributor pickup, plus timing retard if applicable.

I can't remember if on Duraspark pickups if it was an active or passive hall effect sensor but it should literally just be a coil.

It really sounds like a thermal or intermittent fault which is really frustrating to nail down. I'd test with another coil first if you could and if it persists, replace the pickup.
« Last Edit: November 28, 2019, 01:07:48 AM by MIPS »


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