I have been diagnosing an intermittent miss in my #1 cylinder and have found the problem to be inside the distributor cap.
First a little history:
About 10 years ago, the plastic cover that goes inside the distributor (under the rotor) and covers the coil and all internals broke, so I removed it and have been running without that cap all this time. I’ve never had a problem until now.
About two months ago as part of a regular tune-up, I replaced the Cap, rotor, and plugs. The Cap and Rotor were standard off the shelf Autozone stuff (not the greatest), and the plugs were NGK (mid-level).
Last week, my car developed an intermittent miss. it happens mostly when accelerating from a stop, or under load. at high RPM and freeway speeds, it is not noticeable.
I replaced the ignition wires with some decent BOSCH wires since they were not changed with the tune-up.
The problem continued.
In diagnosing the problem, i disconnected the spark plug wires one at a time with the engine running.
For cylinders 2-4, unplugging the wire from the spark plug resulted in the spark arching from the end of the cable to the valve cover anytime it was near the valve cover, and Nothing (except an engine miss) when pulled away from the valve cover.
When I unplugged the cable for cylinder #1, I immediately started to hear the pop-pop-pop of arcing INSIDE the distributor. Holding the end of the cable near the valve cover did not produce any spark from the cable to the cover like the rest of the cables. just the constant pop-pop-pop of the arcing inside the distributor.
When I opened up the distributor, I can see a burnt mark in the metal casing inside the distributor where the spark has been arcing from the #1 post, to the metal where the coil bolts to (the piece of metal closest to the #1 post on the cap).
My gut feeling is to throw the autozone cap and rotor in the garbage where it belongs and go get a decent cap/rotor. But I was just curious if anyone has had similar experiences due to running without that plastic cover inside the distributor.