1987 LeSabre 3.8L... ICM Testing - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 01-04-2014, 05:22 PM   #1
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Default 1987 LeSabre 3.8L... ICM Testing

So! After getting a Code 41 (Camshaft Sensor) and failed restarts when the engine was hot, I replaced the cam sensor with a BWD-Remanned unit. After a few days of flawless driving, the car stalled while braking on an exit ramp. Engine had two failed restart attempts, third time worked, SES illuminated, and I continued the remaining two minute drive to my destination. Checked for codes, another 41 was stored.

I then had no further problems for a day or two. Then, the car would not start at all in my driveway. (Thankfully, I didn't need a tow!) Knowing the history I've had with BWD parts, I ordered a brand-new AC Delco cam sensor, and installed it, and since then I have not been able to start the car.

Knowing the dubious reliability of the Magnavox ignition system, I wanted to verify proper operation of the ignition module. I went to the sticky on Ignition Module Testing, took copious notes, drew diagrams, and looked forward to what seemed to be an easy check. Not-so-much.

So, my first check verified that I had proper 12VDC power to the module. No problem.

My second check was to verify proper ground to the ICM. At this point, following the testing procedures, I discovered there was no ground. I then checked the "ECM ground through ICM" lead, and there was indeed ground there.

At first, I was overjoyed that it was just a bad ground. So, I took a wire, spliced it into the wire that is supposed to be the ICM ground, and... NO DICE.

So I pull out my ol' Haynes manual (yeah, I know they suck...) and look up the ignition module wiring. Surprise, there are some differences, not only in connections themselves, but also in the wiring colors.

Can anyone lend me their expertise? I'll include photos for reference. I didn't want to get too far into it without some expert opinions, plus it'* 20 degrees and I'm standing in 4" of snow... But I urgently need to get the beast back on the road.
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Old 01-04-2014, 05:27 PM   #2
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Default Oh FML

Never mind. I have been told I must register the truck instead of fixing the car that is already registered. Nobody understands that the truck costs more money to register and make roadworthy than fixing the Buick, so it has to wait. Sorry to waste your time.
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Old 01-04-2014, 06:12 PM   #3
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Aaaaand, I'm back. Another knock-down, drag-out... So here are the images I promised.

The Haynes manual data is reproduced without permission, but with All Rights Reserved. Etc, legal mumbo jumbo, yada yada yada.
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Old 01-04-2014, 06:16 PM   #4
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Old 01-04-2014, 11:32 PM   #5
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the early ones were different. i think they started changing to the ones they use now in the early 90'*. i have no diagrams for that one, but when i was searching before i think i came across a person or threads that said they converted it to the newer style for expense and reliability. you might at least find the right wiring diagram on a thread like that
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Old 01-05-2014, 01:30 AM   #6
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I've seen a page with that conversion done, (Swapping your Magnavox Ignition to the delco Type II system : Performance) and I definitely want to do that if my module is indeed bad. I figure the cost will probably be about the same, and I know the newer system is much more robust.

I'm not sure if it'* the ignition module, but this car was already on its second ICM and Coil when I got it two years ago, with 110K miles. Early this year, I had to replace my harmonic balancer and bought a NEW ACDelco crank sensor and changed that at the same time.

I've inspected the wiring and re-seated the connectors. No luck there. There is, of course, the possibility that the cam magnet popped off (or turned to mush, I read of that happening somewhere on the 'net) and I got all excited when I read the sticky on ICM testing, I thought this would be a wonderfully convenient way to check both signals from the crank sensor as well as the cam sensor... But if the pinouts are different on my car, I don't want to go probing more wires until I know which ones should have pulsing voltage when I turn the crank.

Meh, with my luck, I should've known it wouldn't be that easy.
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Old 01-05-2014, 01:33 AM   #7
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I found this discontinued item: {Equus Ignition Module Tester}. Do you know of anyone who has used this, and if so, is it worth the investment? I've heard they are of poor build quality, but the way I see it, it'* pretty much a seldom-used tool.
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Old 01-05-2014, 10:51 AM   #8
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if that thing is correct the wiring must be the same, all they did is plug it in to the newer unit
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Old 01-06-2014, 02:16 AM   #9
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Justin, that'* what I assumed. But you know what they say about assumptions...

So, if my electronics training from '96-'97 stayed up in the gray matter... An internally-grounded pin (which is supposed to be ground for the Cam and Crank sensors) not showing a ground, my options are: 1) CUT the wire for ground on the harness and provide external ground for the sensor, or 2) replace the ICM. That is under the assumption that the Haynes manual is correct, and I admit I have mixed results with Haynes' accuracy. I'm not quite willing to hack the factory harness quite yet, since I can't be absolutely sure the diagram is correct, or that the data on that page is absolutely correct either.

I get the impression that the upgrade was performed on a slightly-later 3.8, when GM moved the ICM/Coil assembly to the front of the motor. I think they started that in... '88? I doubt a few years' difference would mean a vast change in the setup; after all, retooling an assembly line is costly, design changes are also pricey, which is why GM standardizes so many parts across so many of their vehicles. But GM has done some really idiotic things over the years (in my opinion) so a drastic change is not unheard-of.

A quick Wikipedia check shows '88 had the 3800 "Pre-Series I" (with a few LG3 3.8L released as well for '8 and the '87 had the LG2/LG3 depending upon type of lifters. I have to guess I have the LG3, because as far as I can tell by viewing through the oil fill, I *think* it'* roller lifters. I really have no idea, that'* a little beyond my expertise.

I love this car, it would break my heart if it becomes a money pit like my mother'* '87 Pontiac 6000 */E. OMG what a horrible car that was... It was such a lemon that I could put Country Time Lemonade out of business.

Right now I do have the option of slapping a temp plate on the Mighty Max, kinda have to now because I got stopped the other day driving on the Buick plates. So I gotta get insurance, get the temp plate, so I can get back and forth to work. Gotta change 3 dry-rotted tires, figure out some front end sloppiness, plug some exhaust leaks, and replace a freakin' $387 "Idle Speed Control (ISC) Motor Position Sensor" to get through emissions in three weeks.

Never again will I gripe about a $60 IAC Valve for a GM.
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Old 01-06-2014, 07:27 AM   #10
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if they both places say its supposed to be ground i would take the harness apart and follow the wire back and see what it goes to, may just need cleaned
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