95 4.0 Intermittent Cylinder 4 Misfire

[ratdude747]

Been fighting an intermittent misfire on cylinder 4. Usually happens right after startup when cold, but I have had it start doing it when warm. Always under load, pretty much never at idle.

The only code I'm getting is for cylinder 4 misfire.

I pulled the spark plug. The gap was excessive but there still was platinum on the tips, so I regapped the plug to no avail. Looks to be running lean or normal (tan soot, some areas clean)

I re-tightened the lower intake, and replaced all the hardened gaskets on the upper intake. I did not remove the fuel rail nor did I do anything with the fuel rail intake gasket.

I've run a handful of fuel injector cleaners, with no lasting differences. Not so say a hanging injector is ruled out, but it seems less likely?

I was able to get some O2 sensor data with it misfiring... the Bank 2 data is a hot mess, which might be an O2 sensor issue (or just another symptom)? Pictures attached.

At idle (or when not misfiring) the O2 sensor data looks "normal".

At this point I'm stumped... tempted to try plugs and wires, but I don't feel good firing the parts cannon for stuff that isn't cheap.

 

[ratdude747]

Fingers crossed, but I think I fixed it. Plugs were in worse shape than I originally thought... replaced them and also put a new set of wires on.

Idles like a kitten. I'll see tomorrow if it holds.