'89 GM 4.3 liter, weak spark won't start. I might go crazy! - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-07-2009, 04:34 PM
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'89 GM 4.3 liter, weak spark won't start. I might go crazy!

I have an '89 s10 with a 4.3 v6. It will pop off for a split second and then die. It will only pop off one time after you let it sit for many hours.

I have replaced the coil and the ignition module. It has newer spark plug wires and spark plugs. When I pull a spark plug out and arc it out, it has a weak spark to it but will not fire. I can persuade it to run if I catch that first little fire after it sits for a day or two. It is getting plenty of fuel also.

Seriously guys this truck is going to make me sick to my stomach with its antics. I have been messing with it for months. Its my wifes late fathers old truck. It only has 115,000 miles on it so its not to worn out. Any gm experts out there? Any help with this thing would be awesome. Thanks fellas.

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Old 09-07-2009, 04:58 PM
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Have you checked the timing? Could be the chain jumped. JMO. Cole
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Old 09-07-2009, 05:05 PM
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I originally set the correct timing when I pulled the distributor. When it does actually start it runs and drives fine. It turns over nice and fast as well.
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Old 09-07-2009, 05:18 PM
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Does your truck have a resistor that hooks up to the coil that is mounted on the firewall? This is a ceramic type resistor. I would change that. Basically, the ignition system is suppose to supply 12v to the coil for starting and then drop the voltage to help save the coil. If you can find this resistor, just bypass it just to see if it helps. If it helps, you need to replace the resistor. Don't run long without it, it will burn your new coil out.
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Old 09-07-2009, 05:26 PM
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Quote:
Originally Posted by S10 Racer
Does your truck have a resistor that hooks up to the coil that is mounted on the firewall? This is a ceramic type resistor. I would change that. Basically, the ignition system is suppose to supply 12v to the coil for starting and then drop the voltage to help save the coil. If you can find this resistor, just bypass it just to see if it helps. If it helps, you need to replace the resistor. Don't run long without it, it will burn your new coil out.
Im not really sure if it has a resistor. Do you know what it looks like? The wires coming off of the coil go to the ignition module i think. I'll check it out.
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Old 09-07-2009, 05:28 PM
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Another thought I just had was your ignition switch. When the ignition switch is turned to the "start" position, your coil should have a full 12v to it. When it is in the "run" position, the coil voltage goes through the ballast resistor I was talking about in my other post and drops the voltage down. You problem may be that the coil is not getting full voltage on start. You could try the old school way of "hotwiring" the coil to see if it will start. If hotwiring the coil works, the problem is either the ignition switch or maybe a relay.
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Old 09-07-2009, 05:31 PM
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It can also be low voltage to the charging system too. And it could be ignition module also. Cole
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Old 09-07-2009, 08:25 PM
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The ignition module and the coil are both good. I replaced both with new with no change. How do you "hotwire" the coil? I think I should try that and look for that ballast resistor tomorrow.
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Old 09-07-2009, 08:41 PM
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Quote:
Originally Posted by scapegoat
The ignition module and the coil are both good. I replaced both with new with no change. How do you "hotwire" the coil? I think I should try that and look for that ballast resistor tomorrow.
Is the coil externally mounted or inside the distributor cap? If externally mounted, just run a wire from the positive terminal of the battery to the + side of the coil. Same principal goes for a coil inside the cap except that you will need to splice into the wire that is suppose to supply the coil with 12v when the key is on, normally this is a red wire I think.
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Old 09-08-2009, 01:55 AM
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I don't think your 89 has a ballast resistor, so "hotwiring" the coil isn't something that's going to help you.
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Old 09-08-2009, 03:44 AM
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Quote:
Originally Posted by benwantland
I don't think your 89 has a ballast resistor, so "hotwiring" the coil isn't something that's going to help you.
Even without a ballast resistor, hotwiring will tell whether he has an ignition problem or something that is causing the coil to not be getting a full 12v at startup. It's worth a try.
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Old 09-08-2009, 06:13 PM
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Try running a wire from the battery + terminal to the batt terminal on the hei and see if it starts.
Sounds like you have a bad connection somewhere and once it heads a little it takes time to cool. Also make sure all the engine grounds are good. Test voltage from the batt wire on the dist to the dist body. If it is low check to the neg battery terminal with the batt wire at the distributor. I have seen a lot of ground issues on those vehicles
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Old 09-08-2009, 06:36 PM
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Quote:
Originally Posted by T-bucket23
Also make sure all the engine grounds are good.
Man oh man, ain't it the truth. I don't know how many times in the past I have chased an electrical problem only to find that I had bad grounds. Clean off the battery + and - terminals and install new cables. Clean and scrape down to bare metal before attaching the other ends. You need a ground from body to frame and from frame to motor. Get two new ground straps and attach if you have to. Until you do this, you'll be chasing your tail forever and not find the culprit.

I remember a fellow on one of these forums a few years ago who discovered that the positive cable from battery to solenoid was decayed down inside the cable where you couldn't see it. He replaced everything in the electrical and charging system before someone suggested replacement of the cables. Bingo, problem solved.
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Old 09-09-2009, 11:19 AM
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I went to run power directly to the coil but dont know where to run it to. Back in the day there were just a positive and negative side of the coil. This coil has a little mini wiring harness on it. I cant figure out where to run hot wire to it. I think on one side there was a white wire and a red wire and im sure that it was the positive side. Its just that if i unplug that side and run a hot wire to the hole where the red wire plugs into the white wire will be disconnected. Do i need to have this white wire plugged in while i hot wire it? Because the white wire and the red wire are on the same plug. I cant unplug one or the other. Here is a pic of what the coil looks like.
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Old 09-09-2009, 11:41 AM
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Another thing the "newer" GM HEI is known for is the reluctor magnet cracking. It causes a rash of different issues, such as weak spark, no start, random missfire, start and stall, and the list goes on. Pull the rotor off, and look for cracks in the magnet around the dizzy shaft. They can be difficult to see, as you can only see a very small part of the magnet.
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