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What Causes Ignition Modules to Go Out?

G

greg mgm

1/2 ton status
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Apr 6, 2005
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Location
Pine Cove (near Idyllwild) CA
78 GMC Truck 454.

Several years ago, the ignition module went bad in my truck. When the engine got warmed up, the module caused a no start condition until the engine cooled down. Replaced the module and all was well.

2 Months ago, same thing. Replaced the module, then all was well.

Yesterday, the engine ran OK until after a short freeway run. Then it sputtered and backfired....Short story, bad module....again. Replaced it, then it ran great again. Very frustrating.

So....what can cause a module to burn out? Any ideas would be appreciated.
 
my truck did the same exact thing thursday night and i think its the same problem as you. my question is how do you know for sure its the module? can advance or autozone test them like they can alternators?
 
They don't last at all if you don't put the goop on the bottom when installing it. That helps them dissipate heat. Another problem could be the coil shorted on the primary side. You could check that with an ohmmeter, but I don't remember the acceptable range any more. Also, AC Delco lasts longer and works better than any other brand in this case.
 
dfl701 said:
my question is how do you know for sure its the module? can advance or autozone test them like they can alternators?
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Yes, they can test them. I'm not sure how accurate their testing is, but they'll test it. General symptom feels like it's vapor locking. Symptoms can vary and sometimes it just won't even start. THE most common failure in an HEI distributor.
 
All GM engines with an ignition module are HEI, the early engines used the large coil in cap HEI and the later engines used the small HEI with external coil.
 
4X4HIGH said:
All GM engines with an ignition module are HEI, the early engines used the large coil in cap HEI and the later engines used the small HEI with external coil.
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And your point is? Nobody said otherwise. Are you reading these before you respond?:doah:
 
throttleissues said:
And your point is? Nobody said otherwise. Are you reading these before you respond?:doah:
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Dude, you need to back off. Yes i read EVERYTHING before i replied. I just reread your reply though and mistook you for saying that "THE most common failure in an HEI distributor" i read too fast and thought it said IS an HEI distributor. My bad. :doah:
 
dfl701- Autozone (at least in So Cal) has an ignition tester that simulates driving conditions...an expensive machine. When I went through this 2 months ago, the problem was intermittent...the worst kind of problem! Everything else on the engine tested good, and the module tested good as well. I had spare coils, caps and rotors, which were replaced one by one. Right after I replaced the module, the engine fired up and ran great. Yesterday a mechanic did the work and the module tested bad for him. Symptons can vary which makes diagnosing this kind of tricky. This last time, the engine wouldn't run at lower RPM's and sputtered a bit.

Throttleissues- Yup, applied the goop! Dialectic grease, I think it's called, and it usually comes with a new module.
I can't remember the ohm range (it's in any Chilton manual) but my coil was OK each time. I wish they shorted out like you said....at least I would know what caused the module to go out.

Quote-"All GM engines with an ignition module are HEI, the early engines used the large coil in cap HEI and the later engines used the small HEI with external coil"

Thanks for the info.

At this point I'd consider swapping my distributor for ANYTHING that's 100% reliable. I don't mind driving an old truck, but having it burn out modules isn't fun!
 
4X4HIGH, sorry for being such a dick about it. We now return you to your scheduled programming.
 
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Greg mgm- thanks for the info, i will try it i guess just to see what happens.

i just bought my truck so im sorta wondering if i should go ahead and replace the coil also. from what it sounds, the two go hand and hand.
 
Well Greg, my module on my 'burb went out again. I had gone the convenient route and bout a module from Autozone. It lasted 20 months, which is less than 10k miles on that truck.:( I would recommend finding someone who sells Delco modules, but it seems like nobody near me carries them any more.:angry1: I could feel the difference in performance, in that I lost power when I replaced a Delco with a Duralast.
 
I posted this on another site as well, just to get all the info I can about the dreaded "BURNING MODULE" :laugh:

dfl70- The mechanic who worked on my truck yesterday said he won't change a module without changing the coil.....Also, on the other site I posted on, a guy mentioned that his '77 truck blew modules all the time and carried extra modules for a quick change if needed. After he switched his Accel coil to a stock GM coil it stopped blowing modules. My thought was a complete Accel distributor should have been reliable as a brick. My opinion would be to change both module and coil.....but DANG I hate changing stuff that tests good...

Throttleissues- Are you saying your module blew today? Man, I feel your pain :( Yes, I completely agree about Delco. I've bought from Brightauto.com, who carries Delco products online. No surprise you felt a performance decrease with the brand change. I'll definitely steer clear of Duralast modules. My truck idles MUCH smoother with the new module...but I think the mechanic used a NAPA unit. I have no idea on NAPA module quality, but their other stuff seems fine.
If I have more problems with modules in the future, I may buy a complete Delco distributor.....or drive my truck into a river...:haha:
 
so its best to replace the ignition module and the coil right? should i go ahead and do the distributor, i figure so because i wanna do a tune-up. just double checkin
 
Mine actually went out on Tuesday of this week. Napa sometimes carries Delco, but their store brand can be whatever was cheap when they put out the contract.:doah:I've wondered about going to an Accel module before. Haven't known anybody that tried them though. Thanks for the tip about brightauto.com. It's funny that mine idles fine, and only runs crappy under load while yours idles crappy.:dunno: I've seen a lot of different symptoms, but mine's acting just like it did last time the module died.
 
im not sure if its my internet but it says brightauto.com is under construction
 
my ignition module


ignition-500.jpg
 
NewUser said:
my ignition module


ignition-500.jpg
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hey i have that same one.haha.i have never had a problem with my hei besides the little spring contact under the coil going out.i run a accell coil also.im petty sure heat is the biggest issue to why a module goes out.when you connect to outermost pos and neg terminals on the cap.should get reading of 6000-30000 ohms for primary.if not replace coil. the ohms should be close to zero resistance with good continuity frompositive to center pin on cap.then you leave the one lead on the center terminal of the distributor cap and check for continuity also to the tack terminal.use high scale and if both readings are infinite the coil is faulty.that is for in cap coil.outof cap module should be primary 1 to 2 ohms and 3000 -20000 ohms secondary.of course all of these tests should be done with negative on battery disconnected.
 
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