[bowtieguyss]

454 chevy with HEI giving me fits. Missing, popping thru exhaust bad on pass side, ocasionally backfires thru carb, have checked spark, timing, pulled valve cover to see if I had broken valve spring. Bad cam? Not a pro but know that if running rough and backfiring thru carb a lot of times is indicating bad cam.

Thoughts?

[DoubleVision]

Pop the valve covers and fire it up. Carefully eye all the rockers. If you see one or more barely moving compared the others the cam is history.
If the cam is okay, then check the voltage going to the HEI with the engine running. A HEI must get a solid 12 volts or more. They will run on as low as 8 volts, but popping and backfiring is the result. Also make sure there are no crossed plug wires. 5 and 7 run side by side on the block as well as on the distributor and are very easy to cross up.

[stroker444]

On my HEI, the little plug that goes from the shaft to the cap was a bit loose for all three wires. I resoldered the wires and crushed the ends so it was tighter to slide on, now the car runs alot better. Also when I took my plug wires off and reinstalled them, the number 8 plug wire boot was on the plug, the the metal connector slid back inside the boot and i didnt realize it, the result was horrible running.

[bowtieguyss]

I appreciate your input, I did spin it over with the valve cover off and all valves seem to be moving equally. Car ran fine, until we came home from a car show and fired it up to unload from the trailer and it started to miss so it seems that the issue started all of a sudden. Did pull the cap and rotor to see if I had a bad cap or burned spot on the rotor and all looked fine. Will check the current to the dist and make sure I have 12 volts.

[gofastz]

hmmm, kinda sounds like a bent valve? never can tell, i had a 454 and when the rotor button was time to change, it did some popping through the pipes!

[cobalt327]

Originally Posted by bowtieguyss

I appreciate your input, I did spin it over with the valve cover off and all valves seem to be moving equally. Car ran fine, until we came home from a car show and fired it up to unload from the trailer and it started to miss so it seems that the issue started all of a sudden. Did pull the cap and rotor to see if I had a bad cap or burned spot on the rotor and all looked fine. Will check the current to the dist and make sure I have 12 volts.

Was the car left w/the hood open w/o an air filter?

[Bowtie man]

Have the modules in the dist. checked. Sometimes after they heat up they will malfunction.

[bowtieguyss]

No, the air cleaner has not been off. Will have to do a compression test, that should tell me if I have a bent valve. Like I said, it went from running fine when shut off to missing when restarted. Seems to only pop out of the pass side pipe so the issue certainly seems to be to that side.