Re: Need help troubleshooting an ignition problem.

Jul 29, 2003 9 Replies
G

Try replacing the ignition module. Obviously, your truck is failing when hot...did you test your ICM when hot? Nope...



Sam



Hi all;
>
> I've been spending the past month trying to figure out what is wrong
> with my full-size 1986 Blazer with a 305.
>
> Here's the problem:
>
> I'll leave to go somewhere, and it runs fine. I'll shut it off, get
> out, do something, come back, and it won't fire. There's no spark in
> it, and it's getting plenty of gas. After a few hours, it'll fire > right up.
>
> When it first started doing this, we thought it may be the distributor
> cap as it had been raining a lot. So we replaced the coil, cap, and
> rotor. That didn't fix the problem.
>
> So then we checked the ignition module. They ran it through 3 times,
> and it tested perfect every time. So we replaced the pickup coil.
> That didn't fix the problem.
>
> Anyone know what it may be? About all that can be left is a bad
> connection somewhere, right?
>
> TIA
>
> - Rob
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H

The tester used puts a load on the module. By the time they do the test the third time, it's plenty hot. And since we've done that on two seperate occasions, we're fairly certain that isn't the problem.

I checked the wiring yesterday, and it all seems to be in order. I guess we're down to checking on the possiblity we were sold a bad coil.

- Rob

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D

Colorado Springs, CO My advice may be worth what you paid for it.

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M

Sounds like a loose connection somewhere, maybe even the ignition switch itself.

Martin

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"

Hikeeba,

Here's my $0.02. Electrical connections are sensitive to heat. The hotter the temps, the higher the resistance. This is the cause of "heat soak" where the starter turns VERY slowly when the engine is nice and hot (say you pull off the higway to grabe a coke, then restart and it really lugs) due to the starter and wiring being so damn hot.

Because yours is dead only when hot, I'd start looking for wire related to the ignition system that may have made their way close to a source of heat.

Doc

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G

Replace the ICM, or have a tech put it on a scope and tell you for sure what's wrong with it.

No matter how many times you check the ICM on a load tester, it won't even come close to the conditions under the hood. ICMs are the most sensitive ignition part to heat and vibration.

Sam

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H

We replaced the ignition module, and it doesn't appear to have fixed the problem. The wiring is good, everything in the distributor has been replaced, and we have no clue what else it could be. The guy at Napa is wondering if it could be a spark control module or the computer. We don't think it has a SCM, and we're not 100% sure it has a computer. Did the '84 Blazer have either? If not, what in the world else could be wrong with this thing?

Now I'm down to buying something else to drive while I scratch my head...

- Rob

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"

Rob,

1) It doesn't have a SCM 2) It have an ECC if it's stock. Do you have a fully manual carb or a computer controlled carb (will have idle mixture solenoid, 02 sensor, CTS). 3) Read the suggestion made in my prior post.

Doc

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