Hey Steve,

I had an Altima like that last week with an intermittent misfire that would only set a P0300 for some reason. It only happened for short periods of time, but felt localized when it happened, so I was able to isolate it with my Genisys injector kill "special test". A coil swap and retest isolated the defective coil. Why the PCM couldn't directly identify the specific cylinder is a mystery to me.

I have experimented with Nissan COP primary circuits with my Vantage Pro, in search of the cause of the dreaded P1320. Certain COP Nissans and Infinitis are very sensitive to primary ignition concerns, even on a "good-running" vehicle. I have found that secondary issues like plug gaps etc. can show up in the primary voltage waveform, and it's usually a matter of scoping all of the primaries and investigating the oddball(s) through swapping techniques.

Mr. Phelps makes a good point about warm-up catalyst flakiness, which can cause spark plug and valve damage from flying debris being aspirated under certain conditions. I've seen it with my own eyes.

Take care, and keep on scopin'.

Sincerely,

Michael Barry
Technician
Quick Stop Smog & More
Sacramento, California, USA