View single post by Tom Bradley
 Posted: 09-19-2018 06:35 am
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Tom Bradley

 

Joined: 07-15-2013
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 Don- I would fix the problem with oil inside the distributor first. Engine oil is an electrical insulator, so it could keep the spark from jumping between the rotor and the correct connection on the distributor. Also, if the oil is dirty with tiny metal particles, that could also cause the spark to jump erratically. This could not only cause the misfiring you are seeing, but if the spark is insulated from going anywhere, the power could feed back into the coil primary and cause a voltage spike in the ignition circuitry which could cause problems with sensitive electronic circuitry like the Pertronix and the O2 readout. When you fix the oil problem you should also replace the distributor cap and rotor. If there has been sparks getting redirected inside, the cap could be damaged which will continue to cause problems. The rotor is not likely to be a problem, but they are cheap, so I usually replace it with the cap just to eliminate one possibility.

Note on tachometers: The original JH tach measured the current to the coil and converted that to RPM. With an electronic ignition like the Pertronix, there is more power being delivered to the spark plugs, so there is more current going through the tach. So the tach will read high. Otherwise, the tach should not cause problems unless there is a bad connection somewhere in the system. It is a very robust design internally. If you are still using this tach, you should adjust the idle speed using a separate engine analyzer (which measures RPM by counting voltage pulses) so you are not trying to get a good idle a too low an engine speed. Replacing the original tach with a Spidya conversion, which also effectively counts pulses, will also give you a reasonably accurate RPM measurement. But this is a fairly time-consuming job.

If you did not already know, one of the banes of these cars is bad electrical connections, especially in the engine compartment. A quick way to check for this in the ignition circuit is to put a clip lead between B+ on the battery and the + terminal on the coil. If this gets rid of the erratic firing, then you need to go looking for bad connections.

Sorry for the long post. I hope I did not waste too much of your time with things you already knew. Hope it helped.

Tom