Ignition arcing with backdated heat

[Aurel]

Just wanted to document an ignition issue that I just fixed on my 78SC, in case other have a similar issue.

Symptoms: car was intremittently running on 5 cylinders when cold, and had hesitation and misfiring at high rpms when warm.

It felt like igniton related, but hard to pinpoint the exact cause. Since I recently rebuilt the engine, I also suspected the mixture could be off due to higher compression, or timing was not right.

I wanted to recheck the ignition timing with distributor vacuum line off. I doing so, I noticed arcing from the boot of cylinder 6 plug wire on the left hot air duct of heat backdate. Smoking gun right there...

I turns out, the distributor cap is very close to the heat backdate duct plate, which caused the plug wire boot to rub against it. Over time, the vibrations have chipped off the insulation paint on the metal plate, and also thined the boot that was rubbing against it. That was enough to allow arcing to occur, robbing the cylinder from spark.

The fix was amazingly simple: I rotated the wire boot 180 degrees, no more spark and the car runs perfect again.

Lesson learned: I should have checked for arcs in the dark right when ignition issues occured...

[timmy2]

Time for a BFH to use to add clearance to the duct.