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

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

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.

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.

Re: HEI ignition problem help.
 

carbon tracking

Re: HEI ignition problem help.
 

I replaced the old resistance wire to the bulkhead connector with a new 12 gauge wire, my next step will be to disconnect the tach signal wire like you said.

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

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.