Engine sporatically shuts down, then restarts itself...

Engine sporatically shuts down, then restarts itself...

Postby chevyfreakster [OP] » January 11th 2017, 10:36pm

'95 Astro, 2 WD, base unit, 264,000 miles. About six weeks ago, the van began "thumping" at cruising speeds on the interstate. By thumping, I mean total lose of engine power for a split second, then continuing on like normal. This only affects the engine and not the lights, radio, wipers, etc., and happened about twice/day. Being an obvious issue, it's tough to diagnose when it happens intermittently...AND cures itself in seconds. In city traffic, if I'm going under 40 and it occurs, the van stalls, but starts up immediately like nothing ever happened (upon shifting to neutral, that is).

I did the usual web research and it seemed this issue is not linked to Astro vans alone, or even GM vehicles. All makes and models seem to be susceptible and each post explained what "they" did to rectify the problem. Trouble is, there was no common denominator, nothing there that made sense on a large scale...nothing that led me to a specific part. All these drivers reported this occurring after closed loop, never before. Basically, fuel or ignition had to be the cause (most of us can rule out 'air' as the cause). I read remedy suggestions ranging from: new fuel pump and/or filter, map sensor, bad PCM, spider injectors malfunctioning, pinched/loose wire, and of course dist cap, rotor, plugs, and wires, and more. Any of these could cause a myriad of problems, but an engine shutdown for a second? Hardly. Then the plot thickened.

The thumping increased in frequency over the next few weeks. One day, the van thumped, didn't recover, and I had to pull over. The engine remained running, but just barely; it would ping if I touched the gas pedal and not rev up. I turned it off, waited a minute, then it started up and ran just fine. So this new routine became necessary for me to get to work each day. Again, no way to test anything because it all began working perfectly shortly after. This continued until the van refused to restart and tow trucks became involved. My spark tester then revealed no spark.

All over the web, you can read about ICM's (ignition control modules) overheating and going bad. But I'd just installed a brand new distributor in November, with a new ICM and Coil Pickup included. After all this, the "new" ICM was defective. It finally tested negative and I had something that made sense. After replacing it (and the ignition coil, not the pickup coil), the van has been fine. My new dist also had 3 tiny holes (on each side) where my old dist had the screens. I decided these holes (toothpick sized) would get clogged soon and drilled them out to larger than the old dist ones. That should help to cool the ICM.

Once I narrowed this down to the pickup coil, ICM, or ignition coil, I began to read articles concerning those exclusively. Turns out: a failing ICM and/or pickup coil will exhibit the SAME SYMPTOMS. And once the 1st symptom is felt, the unit is toast and will completely fail soon. I also discovered it's a good idea to replace the ignition coil and ICM together, since they rely on each other. Gosh, this is long. Hope it helps someone. (Yes, I know the "gas" pedal is actually the "air" pedal on these vans.)
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Re: Engine sporatically shuts down, then restarts itself...

Postby chevymaher » January 11th 2017, 10:41pm

Check the coil test it and move on to the module second. Test to make sure all the leads to the distributor are doing what they should. Ground power partial power etc. Find a diagram that tells you or search You Tube for someone that has a documentary basically. Telling you how to test each part and circuit. Do a google serch to find test as well.

That is what i got to do.
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Re: Engine sporatically shuts down, then restarts itself...

Postby Lumpy » January 12th 2017, 1:11am

Sounds like an EMP hit.


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Re: Engine sporatically shuts down, then restarts itself...

Postby chevyfreakster [OP] » January 12th 2017, 11:01pm

According to what I've read, an ignition coil can be in the proper ohmage range and still deliver a weak spark. As far as the ICM goes, same thing basically. If the parameters of ohms are within specs, it doesn't necessarily mean the unit is good. It only means that it's functioning. The tricky thing about the ICM's in our vans is: they can get hot and fail...then cool down and run perfectly. If the electronics get too hot, they will expand and lift off the circuit board, losing connections. As the unit cools, they shrink back into their original positions and the unit works again. I took mine (ICM) into Autozone twice for testing and twice they told me it checked out perfectly. A day later, it died its final death and finally tested defective. Can't wait to talk to the store manager at Autozone about the failed distributor...and my towing bills. This time, I installed a Borg Warner ICM. No more cheap crap for me!!! It's too expensive.
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Re: Engine sporatically shuts down, then restarts itself...

Postby AstroWill » January 12th 2017, 11:20pm

Glad you got it fixed, and thanks for posting!

My guess would be that the ignition coil died because of a fault in the secondary ignition system. Spark then takes the path of least resistance, which in turn fried the ICM, then you replaced the dist/ICM without replacing the coil, and the faulty coil quickly fried the new ICM. Once you replaced the faulty coil, and installed a new ICM, all is right in the world. Now if you still have a problem with the secondary ignition system, it's only a matter of time before the new coil bites the dust and the cycle begins again.

If you haven't inspected/tested/replaced your wires and plugs, that would be the next on my list of preventative maintenance.
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