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Stumped on 87 GMC

W

Wraparound

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Allright Gurus,
Can't figure this one out.
It's an 87 with a coil outside the cap HEI setup. A new OEM distributer installed last summer, and a TBI intake.
Occasionally the truck just won't start or will die while cruising. It just cuts out and I have checked it to find that there is no spark. However, the problem is intermitant and all of a sudden the spark comes back and the truck fires right up.
It does not sputter during acceleration or any other time. It does not idle rough and there does not seem to be any pattern to the problem.

Any ideas or suggestions?
 
You got an extra ign module you could try?I know most people will tell you they are either good or bad.I have the other type hei with coil in the cap and had wierd things happen for almost a year before it totaly died.I would be cruiseing down the highway and it was like I let off the gas for a second and then it was fine I thought maybe my foot slipped.Just a thought.JB
 
GM hei sux not sure why but ive never had luck with the system best bet MSD if you have the spare loot....... i havent been in my summit books but the box and distributor shouldnt cost more then $450 and youll never have that problem again ZigZ :cool1:
 
if its an MSD product id just call their tech line........ great buch of people over there915-855-7123 hope that helps

ZigZ :cool1:
 
IT DID IT AGAIN LAST NIGHT

Shut down on my girl while she was out and wouldn't start for two hours. eventually it just fired up again and quit immediately twice. Then it fired up and ran fine all the way home.
What is going on with this thing? A bad coil?
 
might be a good idea to check the entire ignition system. probably a bad coil. if i were you and had some extra cash. i would just replace the entire ignition system. go with msd, seems to be the best system for the money. hope this helps you in some way.
 
Before you spend $$$$$ on ignition and distributor check all the points on the cap and distrubutor. Found a good amount of rust on the distributor points when i did a swap. put a wire brush to the points and get em as shiny as possible.

If you get all new ignition and distributor and you still have the same problem it will most likely be the map sensor. A bad Map sensor will throw off the whole fuel curve and makes the computer guess at the right fuel/air mixture. Even at idle and low rpms it has a big affect on efi.

if you take the ignition wire off and you can't see a good spark when you turn it over then its bad. If you really want to be sure grab it and get shocked...lol you will know if its good or bad real quick.
 
sounds like an ignition module on the way out...
 
i just fixed a similar problem on my 88 TBI and it was the ign pickup-coil, i went through the whole ign. system and found that to be the problem

try that and check the coil if thats good, check the module
i am willing to bet its the pickup-coil
 
I am with blackblazer on this one. Aftermarket pick-up coils are more junk than GM ones(no matter if MSD or not). Replace the pick-up coil and module in the dist. You will see the pick-up coil deteriorating when you do this. I have also seen the reluctor wheel magnets crack as well.

T.J.
 
Thanks for all of your help. It sounds like the same old thing and that really pisses me off because I replaced the whole distributer over the summer. The old one had a pickup coil that looked like rotten fruit. Can't accurately test any components because the problem is intermitant.

You are recommending replacing individual components but claiming aftermarket stuff sucks. What products have you found to be trustworthy?

Will ALDL help me determine the reliability of the MAP Sensor?

I'll update this after the weekend if I track down the problem.

Thanks again
 
Start up and stall immediately afterwards is a sign the ignition module is toast. The GM test for this is to unplug the timing disconnect, and if it starts and runs, the module is bad.

I've had mine die on me and stay dead for an hour or so, then start up like no problem. I am told that at least on GM modules, when they fail, there is some sort of button that pops up to indicate failure, although I have no idea what exactly you'd look for.

The test is easy, although like anything, I doubt it is *foolproof*. Since mine didn't start at ALL, it didn't match the start/stall criteria of that test.
 
Check for trouble codes before you do anything. code 42 is bad pickup coil. No codes other than the usual 12 is a bad module.I have found aftermarket Dist modules espically MSD, are worse and more failure prone than the stock GM modules.
 
ive never once had a problem with a map sensor and if i did the truck would stay running just not great

and if it starts than stalls the pickup coil is shorted or the ign. module is shorted and nds be replaced
 
Had that too

It was the coil. It was excessively loose, and after the engine cut, would poke at it a few times, engine started back up. Bought a new coil, had no problems.
 
If you take off the timing wire and it runs that doesn't mean your ign is toast. could be exposed wires or a short but the ign isn't gonna be bad with the timing wire on then good without. The wires in the dist get exposed from being wedged on the fw. I had to jb weld and rtv mine up.
 
I'm just telling you what GM says is the test for a bad ignition module. Believe it or not.
 
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