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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Rapid Roy on April 03, 2021, 06:45:35 PM
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Engine started running rough this last week on accelerating. Runs normal in Park or Neutral while revving. Runs rough in gear sitting still also. Replaced plugs and the in-carb fuel filter today and no difference. Truck died on the street last weekend and I found a vaccuum hose had split on the end and fell off. Trying to restart I flooded carb and could not start for a while. This flooding may have caused an issue in the carb. The last rebuild was July 2017. Thinking I may need to rebuild again, not sure.
Any help is appreciated.
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Check all of the spark plug wires for hard spots, arcing to ground (grayish-tan ash traces on the outside of the wires) and burn-back (carbon soot) inside the boots. Lift the distributor cap and closely inspect for carbon tracks as well as the condition of the carbon button.
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I have rechecked all vacuum lines, plug wires and all seem good. Pulled dist cap and nothing bad found. Checked fuel lines and cannot find anything I can tell that is causing this. Would a bad ignition module cause this or possibly coil? I have had a no start due to the module before.
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Welcome to the world of variables!
Trying to understand "rough on accelerating"- is it stumbling while accelerating from 0-30 mph?
Q: Did 73 have an ignition control module? I thought those came about later.
Did you pull the cap off the coil and inspect for evidences bd described?
Flooding doesn't affect the carb, it just annoys the plugs... ;D
Finally, have you adjusted the carb idle jets?
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If the module was bad, it's probably the coil too. The coil in my experience can take out the module. Bone stock coil if yours is the internal coil (none of the high "performance/voltage" ones). Unless you find a tester for the coil that gets it hot and puts it in a running simulation, then a simple resistance check will NOT tell if you if it's good or bad.
You may find a tester for the module in autoparts store.
Also, check your grounds.
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If the module was bad, it's probably the coil too. The coil in my experience can take out the module. Bone stock coil if yours is the internal coil (none of the high "performance/voltage" ones). Unless you find a tester for the coil that gets it hot and puts it in a running simulation, then a simple resistance check will NOT tell if you if it's good or bad.
You may find a tester for the module in autoparts store.
Also, check your grounds.
I haven't changed module yet. I have a spare and thinking about changing but not sure if it is the problem.
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Well, I wouldn't change the module until you verify that the module you have is bad OR get a spare, good coil to swap in at the same time. A bad coil takes a very short time to knock out a module.
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So I guess the question about the 'module' is irrelevant?
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My post came right after yours so yours may have gotten missed.
I'd assume since he put HEI in the tag, that he may have converted to it. I'd also assume he ran an appropriate gauge wire with a full 12 volts to the distributor as well if it is a conversion.
Seems like the model year 1975 was the first year of HEI as we know it.
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Thanks 8)
I have read here about "modules" that control knock/detonation by affecting the timing etc.
I don't think that's the same as a HEI (high energy ignition?) system.
I think that was introduced in '73. Maybe wrong but close. Replaced the GM adjustable point system.
So, I'm still wondering what he means by 'module'?
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UPDATE
I performed all the troubleshooting I could do with only having a carport and limited tools. Finally decided to take it to my tech and said my cam had finally worn down that is causing the rough running. He had discovered the #8 cam lobe was worn a few years ago when replacing the valve stem seals. It was worn and only raising rocker arm a little. He is in the process replacing cam. He is going to put in an Edelbrock Performer cam. He said it is the beefiest he could install without any other upgrades which is more than the stock one. Should be finished by next Friday.