I have checked every thing I can think of can anyone add anything ? Problem .. miss fire to one or more cyl under heavy acceleration when warm. This is only occassional and does not happen every time. I have had the timing checked, spot on. New leads. Checked gaps in plugs. New dist cap. No vacumn leaks either. Wondering could it be coil ? or a plug ?

 

if it's happening when the motor get to operating temps rather than when cold my guess would be the coil.
Heat from the engine bay tends to cause coils to cut out when they are going bad that they don't do when they are still at a cool temp.

 

I have a TPI system, driving me crazy for several years, on and off, when cold it would run fine, when closed loop/hot in summer it had more misses than a HS prom....freaking stupid.....ran fine cold, in winter (or what passes for cooler dryer weather here in Florida) it ran fine....even over several miles of freeway,....
engine not overheating, just....

well, turns out it WAS plug wires, and headers, and boots, and crap...
so I just spent 150 bux on a complete set of Jacobs ceramic plug boots and Accell shorty plugs....THAT finally killed the summer ragged as hell running problem....mind you in the mornings it was running fine, get it into closed loop and it fell apart....

THAT combined with one hell of a tip in stumble I am still playing with, was a stupid thing to cope with on a part time basis, what with so many other projects outside the car going on, and then other aspects of the vette also added in...so anyway...

PLUGS?WIRES...first suspect....BTW, my junk was NEW, not that it mattered much....

GENE

 

I agree on the possibility that the plug wires may be the source of your problems. I have experienced similar symptoms and that was the fix. (As stated earlier, the coil is also a good possibility.)

 

oh, one other possibility that is something you may want to try........
No doubt i'll get comments on this the same as I did in the C2 section telling me I'm nuts and that there is NO WAY this could be the problem, but it can be!

what kind of spark plugs are you running? If you are running standard spark plugs most of them now are a resistor spark plug. Try swapping out to a non-resistor spark plug.

Over the winter I did a lot of work on my '65. it includeing rebuilding the distributor, a new distr. cap and rotor, new spark plugs, new ignition wires, rebuilt the carb, and a lot more.
I ended up with a high rpm miss problem.

It was suggested by a good friend that is VERY knowledgable on motors to swap out my new AC R45 plugs that I just put in (and have been using the same type for years with no problem) for a non-resistor plug. Taking his advice I swapped to the NGK B4 non-resistor spark plugs and my miss went away immediately.

The theory behind his reasoning is this:
The original spark plugs on the car were non-resistor sparkplugs. Over the years the AC R45 changed to a resistor spark plug. It was never a problem but then I also changed to new spark plug wires.
It's possible that the higher suppression on the new wires in conjunction with the resistor spark plugs could cause just enough of a voltage drop to cause a missing problem.

He had developed the same problem and installing a non-resistor plug solved his problem.
I tried his advice and put in the non-resistor plugs and it solved my missing problem also.

it's at least something you may need to consider looking into if nothing else solves the problem for you.

 

I fixed it. It was the coil. I fitted a new one and it runs sweet now. Just need some side pipes and it will sound as good as it goes.

 

Plug wires, Plug wires, Plug wires

 

Barry did you have your coil checked?The reason I ask is I had the same problem and it turned out the non-resistor was a band -aid fix because the coil was weak.Replaced the coil went back to resistor plugs and things were good.

 

nope, the coil was #2 on the check list to try if the plugs didn't fix it.
My fried that had the same problem and suggested I try the nen-resistor plugs went thru EVERYTHING first including the coil and nothing worked until the non-resistor plugs so I tried that first.
Had the car out 3 or 4 times already since installing the new plugs and everything is perfect.
BTW, I would think a new coil would more easily mask the problem of a faulty plug rather than new plugs mask the problem of a faulty coil. If it's really the coil going bad, swapping to a different plugs wouldn't help - if there was no voltage or current for spark out of the coil, no sparkplug would be able to mask that problem, but possiibly a newer, stronger coil could overcome and push thru a spark on an "iffy" plug therefore masking that problem. Or so MY thinking would go........

Regardless, IF the problem comes back the coil would be next on my list to look at.

 

Yes I agree with the masking problem but could go either way.Way back then(around 1972)we tried hard to pinpoint problems with no guessing for future information.An ignition that was having trouble firing resistor plugs threw up red flags.I had a small Sun scope back then and we tested in detail including a loaded performance test on the coil.Most standard coils would test above 40,000 volts the coil I was speaking of was below 10,000.I remember because this was a 69 Z-28 that belonged to a buddy that was upset because he could not stay with my 66 vette.He had fought the problem for at least a year because he had undergone a diagnostic check on a fancy smancy new machine that had a "tape readout" a before year.After discovering this we went back and read his tape he had thrown in the glovebox and there it was in black and white-coil performance -below spec.Another thing I used to find on a regular basis was the positive and negative leads switched on the coil-car runs but spark is jumping from side electrode to center and that takes 10,000 extra volts.I'm not saying yours is bad I'm just sharing old memorys.