I have a 67 mustang with a 289 and I'm having some plug misfiring problems. When I got the car, it seems to have a rough idle but I didn't really hear any misfires. Yesterday I installed a new distributor, a new cap/rotor, and plug wires. I noticed a slight ticking sound coming from the passenger side of the engine. I also noticed a slight change in acceleration and a little rougher idle. I installed new plugs gapped to 0.035. This didn't seem solve the problem. The exhaust is now also popping under deceleration. I started the car in the dark and tried to see if there was any arcing by the plugs and i didn't notice anything. What's the correct way to diagnose this problem? Is there any way to diagnose each plug wire? Thanks.

 

check your fuel pressure...sounds like it may be running lean..