Ignition Control Module Experience

[1987 GMC Jimmy]

I always feel bad whenever people post about no start conditions that seem to be ignition in nature, and even though I always suggest that people test and replace, if needed, their ICM, I've never had the issue myself. Well, I did last night/today so I just wanted to share about it. So yesterday morning I took my brother to school, which is about a six mile drive roundtrip, with no problems. I had been doing work back flushing a washer fluid nozzle and installing my third ECM later that evening (factory unit popped an integrated circuit and second unit worked until two rat chewed spark plug wires somehow grounded out to the frame, blew several fuses including the ECM, and damaged the pins on the dist. cap). Anyways, the new ECM was alive and interfaceable so I proceeded to start the car a good many hours after taking my brother to school. It coughed a few times and then nothing. Being overly confident that it was too tip top for a no start condition, I ended up trying to coax it too far and flooded it. So I angrily left it alone for the night, came back this morning, pulled a spark plug, grounded it, and turned it over. No spark. Personally, I like the optical method of testing spark with an inductive timing light, but my timing light gave up the ghost earlier this year, and I was too cheap to get another one until I needed it. All my ignition parts are half a year old Delco components with no hiccups so I pulled the ICM, took it to Autozone, and had it tested. The guy said he tested it four times to make sure his results were repeatable, and it failed all four times. This was the 31+ year old factory unit with 247,000 miles so in the hope that I could somewhat replicate that success, I ordered a Delco ICM that will be in tomorrow instead of getting a Duralast or MasterPro right then that would break in half a year. I expected when it did happen that it would fail gradually (when it was hot only and once it cooled off, it'd work again) instead of all of a sudden in my driveway with a perfect run preceding the failure. But yeah, this is my story with it. Just thought I'd share.

 

[74 Shortbed]

Well, don't have much experience with them since I only had two of them fail in over 35yrs, and both died the same way, was running good and when I shut it off it wouldn't start again, maybe because both times I happen not to have a spare in the glove box, lol, now I have a spare that's almost 20yrs old,lol..

 

[1987 GMC Jimmy]

Definitely a good idea to have a spare, and maybe I'll get one in the next couple years to have as a backup in case this one fails. It makes me worry a little now that it could go out anywhere at anytime, but if it lasts another 31 years, I'll be 50. Haha, one could only hope. I guess the breaker point ignition folks have the upperhand here.

 

[74 Shortbed]

Well, you know if you don't have one it'll take a **** on ya, so you need to get one now so you don't have any failures, lol, they're only $30 or so.. Point deals had their share of failures too, I always carried a spare condenser with me..

 

[1987 GMC Jimmy]

I actually paid $63 for this one because it's Delco. The cheaper ones were the Duralast/MasterPro models, but I didn't want to chance those, especially to quitting in New Orleans traffic, some shoulderless highway, or in some rough neighborhood.

 

[74 Shortbed]

Those are garbage, you can get decent ones cheap too, but for a spare they're plenty good enough to get you home in an emergency. And Delco don't necessarily mean USA anymore, unfortunately..

 

[1987 GMC Jimmy]

Yeah, I know about the Delco. I'm not sure where this particular one is made since it doesn't say. I've had some of their stuff "Made in the U.S.A" and "Hecho en Mexico." I may do that fairly soon, though, because you're right. It's always good to have one of those as an emergency.

 

[74 Shortbed]

Yeah, you never know where anything is coming from anymore, very sad.. If you have a spare you'll never have to use it, which is a good thing, lol..

 

[1987 GMC Jimmy]

@74 Shortbed: New ICM quit on me within about three seconds. I'm not sure if it was defective or if something's wrong with the car. I swapped ECM's to a used but tested unit, but the new ECM seems fine to me. I ordered a new one that didn't make it today, but I saw on the box that it's actually made in this country. I guess I just missed it earlier.

 

[74 Shortbed]

That seems awful quick but could be defective not surprising these days, sounds like maybe something shorted it out maybe??, no bare wires anywhere?, I assume you have a 7 pin ICM never had those just the 4 pin, maybe it is the ECM???

 

[1987 GMC Jimmy]

Yeah, it's the seven pin module. It mimicked what the other one did perfectly. It started, chugged for a few seconds, and that was it. No more spark. I guess it wouldn't hurt to use the ECM that I've been using. It works, but I can't interface with it since some rat induced electrical damage that has long since been repaired. The old ECM's circuits look perfect. I'm gonna try swapping the PROM to see if that does anything, but even if it doesn't work, I think I'm just gonna have to use the old ECM to be safe.

 

[74 Shortbed]

Sounds like the ECM alright, may as well put old reliable back in..

 

[chengny]

Is this right?

You were running the truck with the original ignition module and ECM installed - and life was good. Then one day (fairly recently I am guessing), the original ECM failed. Inspection revealed a board level issue - and that it could not be repaired.

But luckily, you had a spare ECM. You plugged it into the harnesses, cranked the engine - and it fired right up. You resumed normal operations.

For (an undefined) period of time, the module worked as designed and kept the motor running well.

This is where I start to get confused:

Then, out of the blue, tragedy struck again. This was caused when "two rat chewed spark plug wires somehow grounded out to the frame, blew several fuses including the ECM, and damaged the pins on the dist. cap".

The fuses were replaced and repairs were made to the secondary ignition circuit. The replacement module was tested and confirmed okay. The truck was running fine.

For example, you drove your brother to school a few days ago with no problems. Upon returning home, you decided to remove the module - the one that was currently installed - with a third spare module that you had recently sourced. The reason for this replacement was because you could not "interface" with the one under the dash at the time. This was attributed to the rat attack that had damaged the secondary ignition circuit.

But the ECM - the one that was installed - appears to have output control problems. This was thought to be true because;

1. When it was connected to the harnesses - and powered up - the engine failed to fire.

2. Diagnosis of the no-start lead to a shorted ignition control module - which presumably
had been fully functional prior to the new ECM's installation.

You got yet another ECM and installed that - along with a new factory grade ignition control module. The system was powered up and the engine was cranked but failed to fire.

The no-start was found to be caused by a no-spark condition - once again attributed to a shorted ignition control module.

I am sure I have got most of this scenario totally wrong - so please straighten me out.

Stories of repeated (and immediate or extremely premature) ignition module failures have always interested me. And quite honestly - after spending (wasting?) way too many hours on the internet - researching the subject, it remains a mystery.

It appears to me that sometimes no one really knows the reason - other than overheating and wiring/grounding issues. Once those two causes (and rarer causes like moisture and excessive system voltage) are eliminated, there is not really that much more to investigate.

So, most of the time, folks just keep shotgunning the ignition system with expensive parts. Then finally, one day, they get the right combination. And once they have a nice fat blue spark across the plug gap and it stays that way...well that's it for them. They just hope it never happens again.

 

[bucket]

I've had ignition modules fail in a year or less (like a week) and then the replacement lasted for years to come. I don't really think there's something that causes them to fail, other than just being a defective part. It's always been the 7 pin modules too, really no trouble with the older type.

 

[1987 GMC Jimmy]

Is this right?

You were running the truck with the original ignition module and ECM installed - and life was good. Then one day (fairly recently I am guessing), the original ECM failed. Inspection revealed a board level issue - and that it could not be repaired.

But luckily, you had a spare ECM. You plugged it into the harnesses, cranked the engine - and it fired right up. You resumed normal operations.

For (an undefined) period of time, the module worked as designed and kept the motor running well.

This is where I start to get confused:

Then, out of the blue, tragedy struck again. This was caused when "two rat chewed spark plug wires somehow grounded out to the frame, blew several fuses including the ECM, and damaged the pins on the dist. cap".

The fuses were replaced and repairs were made to the secondary ignition circuit. The replacement module was tested and confirmed okay. The truck was running fine.

For example, you drove your brother to school a few days ago with no problems. Upon returning home, you decided to remove the module - the one that was currently installed - with a third spare module that you had recently sourced. The reason for this replacement was because you could not "interface" with the one under the dash at the time. This was attributed to the rat attack that had damaged the secondary ignition circuit.

But the ECM - the one that was installed - appears to have output control problems. This was thought to be true because;

1. When it was connected to the harnesses - and powered up - the engine failed to fire.

2. Diagnosis of the no-start lead to a shorted ignition control module - which presumably
had been fully functional prior to the new ECM's installation.

You got yet another ECM and installed that - along with a new factory grade ignition control module. The system was powered up and the engine was cranked but failed to fire.

The no-start was found to be caused by a no-spark condition - once again attributed to a shorted ignition control module.

I am sure I have got most of this scenario totally wrong - so please straighten me out.

Stories of repeated (and immediate or extremely premature) ignition module failures have always interested me. And quite honestly - after spending (wasting?) way too many hours on the internet - researching the subject, it appears to me that no one really knows. Most of the time, folks just keep shotgunning the ignition system with expensive parts. Then finally, one day, they get the right combination. And once they have a nice fat blue spark across the plug gap and it stays that way...well that's it for them. They just hope it never happens again.

You got it mostly right, but I'll just reiterate the high points. So when I acquired the vehicle, the ECM was already damaged, non-interfaceable and problems with ignition advance to the point that the car was driving poorly. After a lot of diagnosis and troubleshooting, that's when I pulled the ECM and found a torched integrated circuit so I ordered a remanned ECM. After getting the second ECM and transferring the PROM, it worked great. That is, until that rat damage made itself apparent driving down the highway 120 miles from home. You're correct, a couple wires somehow grounded to the frame, caught on fire, and blew my interior lights/dash lights/VSS/TCC fuse and my ECM B fuse. All this happened while (barely) driving down the road on six cylinders. The rat damage consisted of the two plug wires, the melted pin on the distributor cap, and the two fuses, but that was the second encounter. The first had occurred several weeks earlier with one spark plug wire, the distributor 12V wire, and the heater core ground being the victims there. After all the repairs were made, everything worked except I couldn't interface with the computer, which included no SES light test at startup. I did inspect this ECM as I did the first one, and it looked perfect. So yeah, everything was fine, but I didn't like not being able to pull codes, get live data, or see if a light came on while driving. I ran this for several months and bought a used module for peanuts a few days ago just to gamble and see if I could get that interface back. After taking my brother to school with no problems, I pulled my second ECM and attempted to use this third one. I got my SES test, and the computer started flashing away with the insertion of a paper clip so that looked good. As soon as I attempted to start it up, though, the car chugged for a few seconds and was dead, and I flooded it trying to coax it to start. I pulled a plug, grounded it, turned the key, and a no spark condition was found. I pulled the ignition control module, had it tested, and it failed the test. I'm pretty convinced that was the OEM unit because it had the factory style numerical castings in the plastic much like the factory HEI coils do, and it looked really old, anyhow. Anyways, I ordered a new Delco unit, waited a day, and installed it. Same exact thing happened with no modification to my ECM situation. Pulled the new, second ICM, and it tested bad, too. At this point, I'm only assuming the ECM is what caused the failure because that's the single dependent variable in all this, discounting the two ignition control modules. I swapped PROMs to see if that may have been what was wrong in the second ECM and somehow it was using the CALPAK to operate everything, but the PROM swap did nothing for it. Either way, I'll just run the second ECM until I can try again to replace the ECM. I may try to exchange the second ECM at the parts store, but the remanufacturer's warranty had a lot of terms, conditions, and stipulations so we'll see if the store will even take it back. I just don't like dealing with the one where I live, and I only do if the prices are better or if I need to borrow a tool from them since their program is more flexible than their next door competitor's, O'Reilly's. I'll update when I get the third ignition control module in with that second ECM this time. Should be later today, or at least I hope so. I'll also see if I can switch out that ECM with another remanufactured unit. I just really hate dealing with Autozone's customer service. For me here, it's been mediocre at best.