I have pretty much a bone stock L79 other than a Pertronix module in place of the original points setup.

A few days ago the engine got very rough, and I could sense that not all cylinders were firing.
Battery is near new and strong. A test showed that a couple of wires were not sparking. Installed new wire set (what an project that turned out to be. I can see why, in the day, so many guys threw the shielding away.

Problem still there so next I try swapping back the points setup in place of the Pertronix module. Still the same.

Next I try a new coil but that's not the source of the problem either.

I'm currently looking into whether the Ballast resistor might be a possibility. Any thoughts on this?

I've also thought of the distributor but I'm hoping its something else.

If any of you have any experience with this problem, or if you just have an idea of what might be causing it, I'd very much appreciate your feedback.

Thanks much

 

Remove the shielding and see if it goes away.

The resistor works or doesn't work (no in between).

 

for carbon tracking, and take a look at the rotor at the same time. If the electronic ignition modification was used together with the condensor from the points system, this could also be it.

I usually pull one plug wire at a time while the engine is idling (if it misses at idle) to find out which cylinder(s) is(are) causing the problem. If you pull a plug wire off and there is little or no difference in the idle, then that cylinder is not contributing. You should expect to notice a difference in idle quality for any cylinders that are working properly. If it's a single cylinder that is 'missing', then you can concentrate your efforts on that cylinder. If it's more that one, look for a pattern that might help find the problem. As an example, many years ago on my '68 396 Chevelle, I found that 4 cylinders weren't firing, and they happened to be every other one in the firing order. That was an excellent clue. Since the engine had a 2 plane (or 180 degree intake manifold)... each side of the carb fed every other cylinder in the firing order, so I decided to take a look at the carb. When I removed the float bowl from the carb, sure enough... there was a little piece of junk partially clogging the main jet for that side of the carb. So in this case it wasn't even an electrical issue.

I have also had occasions where changing from non-resistor plugs to resistor plugs and also visa-versa solved misfiring problems.

You didn't mention what type of plug wires you installed, resistor or non resistor. Many electronic ignition systems recommend resistor wires because the radio interference caused by the solid core wires can affect the signals that the ignition box uses to determine when to fire the plugs. However, since you switched back to the stock system and still have the problem, I wouldn't expect this to be the cause.

The only other thing I can think of is that you PO'ed one of your friends and he has a model of your Corvette and is sticking pins in the engine. In fact, many times solutions to electrical problems seem to be more voodoo than common sense. Good luck.

 

Sorry, forgot to mention that I also tried installing new rotor and distributor cap. No change. Also removed, inspected and cleaned all spark plugs (resistor type). Plugs were like new, with no signs of any defects.

 

The Pertronix unit is sensitive to low voltage(12v to the red wire). Make sure your battery is fully charged and see if that helps.