Burning Up Ignition Modules

[David Floyd]

I have a 1987 half ton Chevy Suburban 4X4 with a stock 350 (my beloved "Ghetto Winnebago"). The engine was replaced at a GM dealer at 187,000. It now has 248,000 on it. My problem is the ignition module keeps going bad. I have replaced the cap, rotor, plug wires and O2 sensor. When I put in a new module, the truck just purrs like a dream. But the last time I changed the module it died after less than 2,000 miles. I don't use cheap parts to save a few cents. I'm not much of a mechanic so any help on how to fix this problem would be greatly appreciated.

[ratlover]

did it die once and then you drop another unit in there and it die again in 2k?

Anything else get zapped? What plug wires are you running?

What brand stuff did you put in there exactlyy?

You might just have bad luck

[David Floyd]

It starts by dying sporadically, usually when you're rolling along. After a couple of minutes it will start up again and then run fine. Then the dying becomes more frequent and after 4 or 5 times it won't start again. The plug wires are Borg Warner and I'm not sure of the brands of the other parts. I usually always get the best quality Pep Boys or Advanced Auto Parts has to offer.

The ignition module seems to be the only part that goes out and needs replacing. I don't think it's bad luck because I've had to put in four ignition modules in about 3 years. The bad thing is they seem to be going bad much quicker these days.

[wyldman]

The ignition module has no direct relation to the wires,or any secondary ignition parts for that matter,so don't worry to much about that stuff.

The ignition module must mount solidly to the distributor base,with a thin layer of heat sink compound,or silicone di-electric grease under it to aid in heat transfer.If the mounting screws are stripped,or the dist base or module is dirty corroded,you may not have good contact,and the module will overheat.It may also have a bad ground,as it grounds through the screws.

I'd take it off,and clean both surfaces,and re-install it with some heat sink compound so it will not overheat.Make sure the screws are clean and tight,so it gets a good ground.

The other possible causes could be a bad ignition coil,or a pickup coil assy.The primary resistance of the ignition coil may be out of spec,causing excessive current draw through the module assy.The module basically just controls the current to the primary side of the coil.To much current will kill the module.The pickup could also be shorting out,but i'm not sure if it would damage the module or not.

You can test the coil and wiring with a voltmeter.Remove the small external two prong plug from the ignition module.With the key on,measure the voltage between both terminals (one at a time),and battery ground.You should have battery voltage on one,and slightly less on the other.If you have less than 10 volts on both,then you have a bad wire to the ignition coil.If you have 12 volts on one,and less than 10 volts on the other,then the coil is bad.

[Backcountry]

You may be able to use the heatsink material that they use between a computer processor and heatsink. It is called Arctic Silver. Also alot of electrical related problems are ground related.

Good luck!

Guy

[phoenix827]

Over voltage?

[David Floyd]

I think Wyldman is on the mark. I bought this Suburban from the original owner and he kept every receipt for everything done to it. I've done the same and I've logged it all in an Excel spreadsheet (what can I say, I'm an anal-retentive slob). So I was able to research the history of the ignition modules and ignition coils. I had the ignition coil and module replaced in May of 2000. That's when it all started. In Dec 2000 I replaced the ignition coil and module again. Then the ignition module was changed out in Jan 2002, Apr 2002, Nov 2003 and Mar 2004.

When you change out the ignition module it doesn't come with new screws. Wyldman says they need to be clean to ground properly. I'm going to pull it off and ensure the screws are clean. I've always cleaned off the contact point and used the silicone grease that comes with a new module so I don't believe that's an issue.

Based on Wyldman's suggestion, that leaves the ignition coil (which has been changed a couple of times) and the pickup coil assembly. I'm not sure what the pickup coil assembly is so I'll have to research that in my Haynes manual.

I'm going to test with a voltmeter and see if I can pinpoint the problem. That means I get to bust my cherry on voltmeters which I know nothing about. I'll see if I can find one that registers up to 1.21 Jigawatts...

[wyldman]

The pickup coil is inside the distributor,under the rotor.It's cheap ($20),but the distributor must come out,and the shaft removed to replace it.After that,it just a small clip that holds it in.

Although it sounds hard,it's actually a pretty easy job.I can do one in under 15 mins.