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09-28-2021, 08:22 AM | #1 |
Registered User
Join Date: Jul 2017
Location: herminie, pa
Posts: 305
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HEI ignition problem help.
Hi everyone,
My car has developed a high rpm/ high load miss, can someone help me work through it. It's in my 67 Biscayne with a Chevy 350 and an HEI distributor. I have a good 12v to the HEI, and I did all of the basic resistance checks on the coil and pick-up, and those checked out ok. Im also having some trouble with my tach being very erratic, aftermarket Bosch. Sometimes the tach needle will swing up and down a thousand rpm while the engine is cruising steady. And sometimes the tach will bounce up and down while the engine is misfiring. I don't know if the two issues are related, but it gives me something to think about. Could my tach be shorting out, causing a misfire? Or is the tach just reading whats happening with a dying coil/ module? Thank you
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2012 GMC 2500hd/ 6.0 1972 Chevrolet c20 350/350 1986 Chevrolet Monte Carlo SS/ 6.0 lsx |
09-28-2021, 04:31 PM | #2 |
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Join Date: Oct 2005
Location: Overland Park, Ks.
Posts: 5,190
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Re: HEI ignition problem help.
I would look at the spark plugs & check the plug wires, dist cap. & rotor. It sounds like a high tension breakdown. Also could be a carb problem.
George |
09-29-2021, 09:31 AM | #3 |
Msgt USAF Ret
Join Date: Jan 2005
Location: Kalamazoo, Michigan
Posts: 8,703
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Re: HEI ignition problem help.
How are you feeding the HEI distributor BAT terminal. If you are using the old coil resistance wire you will have to replace it with a new wire from an ignition on power wire.
I would just disconnect the tach wire at the distributor and see if anything changes with the misfire. Like wrench says, it could be a carb or plug problem.
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VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative. |
10-04-2021, 06:01 AM | #4 | |
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Join Date: Jul 2017
Location: herminie, pa
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Re: HEI ignition problem help.
Quote:
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2012 GMC 2500hd/ 6.0 1972 Chevrolet c20 350/350 1986 Chevrolet Monte Carlo SS/ 6.0 lsx |
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09-29-2021, 03:47 PM | #5 |
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Join Date: Aug 2012
Location: Oklahoma City, OK
Posts: 2,461
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Re: HEI ignition problem help.
2nd on pulling the tach wire. If that doesn't work, try a new set of plugs. I chased a similar issue on a 79 Camaro. The carb and plugs were both new. After a session of getting the carb setup, it developed a high speed miss. After chasing a bunch of other things, tried a new set of plugs. Problem solved. Best guess is I developed "High Speed Glazing", described in one of the lower panels in the How to Read Your Plugs photo array. Basic idea is the plugs have a light coat of black carbon from running too rich then are subjected to high heat from running too lean. The carbon turns into a thin coat of conductive material that looks like a good plug color. Something that might happen while adjusting a new carb. I guess by then I had the carb adjusted good enough as the problem didn't happen again.
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09-30-2021, 06:11 PM | #6 |
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Join Date: Dec 2018
Location: Clitherall
Posts: 56
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Re: HEI ignition problem help.
carbon tracking
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10-04-2021, 02:06 PM | #7 |
Registered User
Join Date: Jul 2017
Location: herminie, pa
Posts: 305
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Re: HEI ignition problem help.
So just a quick update. I replaced my plugs and wires. And I still had a mis in conjunction with a wonky tach. I disconnected the tach and the mis was still present. Then I replaced my coil with one I had laying around. The misfire went away and my tach is acting normal again. So I don't know what to make of that. Even with my old coil, my plugs made a good spark and the old coil passed the standard resistance checks. But the car appears to be running better...sooooo, I don't know what to make of that
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2012 GMC 2500hd/ 6.0 1972 Chevrolet c20 350/350 1986 Chevrolet Monte Carlo SS/ 6.0 lsx |
10-04-2021, 07:48 PM | #8 |
Senior Member
Join Date: Apr 2016
Location: Cypress, TX
Posts: 3,513
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Re: HEI ignition problem help.
Sounds like you found the problem, that's what I make of it. Good deal. Resistance checks may not tell you the whole story.
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