A recent PM conversation reminded me of a problem that's associated with 6 cylinder HEI systems. An open-circuited or high resistance plug wire in certain positions on the HEI distributor with the coil in the cap can cause the high voltage to jump through the insulation of the cap to one of the screws that attaches the coil. It creates a tiny pinhole that's almost impossible to see, and the miss only shows up initially on a hard pull such as a long uphill run, or accelerating to pass, etc. Eventually it becomes a pretty constant miss that can't be fixed with normal tune up procedures. The V8 caps don't have the problem because the screws and the plug towers aren't close enough together to cause a problem. Back when GM had the odd-firing 231 cubic inch V6 in the Buick and Oldsmobile compact cars, this was a pretty common problem.
Jerry
