Cylinder #7 misfire when HOT???

[Roadracing7]

'97 5.0L

Flashing check engine light, stopped at AutoZone, found it was "misfire cylinder 7". So I got home pulled the plug and it was clean, not dirty, gummy, white, detonating... it just looked normal. Oh well, replaced it anyway.

Pulled the #7 and #4 wire and resistance both were about the same.

Moved the #7 wire to cylinder #8 and vice versa. Went on a test drive and here comes the flashing check engine light with some more codes to pull. If it's misfire cylinder 8, I'll just get new wires all around and switch coil packs/bank.

My confusion lies in the fact that when I crank it in the morning, it runs great until it gets to normal operating temperature. I'm sure the ECU is changing mixture depending on air and water temp, but when it hits the operating temp it starts to mis VERY noticably.

It misses at about 1500rpm with about 25% throttle, but not at 2000rpm at 10% throttle. Am I chasing ignition when it's fuel? The only cylinder specific I can imagine is an injector... If that's the case I should see a "misfire cylinder 7" at autozone right? But that could also still be that port on the coil... I'm headed in to work and will stop at autozone... any other ideas???? HELP!!!

 

[Hokie]

Sounds like you're on the right track. Just keep trying things to see if you can isolate the issue or get it to move to another cylinder. ie: if swapping wires keeps the mis-fire on #7 then it could be the coil or it could be the injector

For me, my mis fire was burnt insulationg on a plug wire (the Ford tech that installed the wires before I bought it had a rubber part of the wire close to the exhaust manifold and 40k later it finally degraded/cracked)

 

[Roadracing7]

How to fix:

It's fixed, turned out to be the #7 wire, but I would have done things differently. If anyone searches and finds this, here's what I should have done:

Switch the #7 wire with the #3 wire (opposite bank)
Switch the #7 plug with the #1 plug (opposite bank)

When I switched with #8, I could have gotten the miss on #7 still and it be caused by either an injector or coil pack. Now:

If it's #1, it's the plug.
If it's #3, it's the wire.
If it's #7, it's the injector.
If it's 5,6,8, it's the coil pack. (test resistances of course to be sure)