I have a miss at idle.. Seems to run fine from 10 up mph. Number 5 and 7 spark plug wires I can take off and it makes no differenece, but plug is firing. 150 psi of compression on these to cylinders. Plugs and wires new, distribitor cap is new. The timing is right on. It was running fine one day when I parked it. The next morning when I started it, it missed. Please help before I start taking the engine apart as I have no idea what to do next. Thanks

since these two cylinders fire one after the other, I would look in the dist cap to see if there is a crack or maybe some carbon tracking between the two cylinders inside the cap.

Vacuum leak between those two cylinders at the intake manifold maybe.

Sorry, but it is # 5 and # 8 missing. Should all so mention that it a point type distributor. This a 1970 El Camino with a 350 Hp. I'm lost.

still could be a vacuum leak, don't those cylinders share the same intake crossover runner?

Any carbon buildup on the rotor or in the cap?
Have you tried swapping wires to see if the problem follows?
Did the problem exist before the new cap and wires?

Before you go tearing things apart, replace the plugs, wires, cap, etc.....a lot cheaper and less frustrating. Sometimes you can't see what is wrong with these parts.

I can honestly say I have installed a dist cap and it was bad from the first time the engine was cranked...you couldn't see anything wrong with it. Same for a spark plug....once on a car and SEVERAL times on lawnmowers(the ole CJ8), it was a brand new plug that didn't fire like it should.

I'm gonna bet it's a bad plug wire. I would go to Auto Zone or where ever, buy 1 wire, and start with replacing the #5 and 8 wires on your engine. I'll keep my fingers crossed.

Good luck! Let us know what you find out. smile.gif

Are you running your pcv off the fitting on manifold behind carb?

are you running headers? are the plug wires resting on the header tubes? what size mm wires are you using?