I have a 2000 Expedition with the 5.4L and I get an OBDII error code of p303 which is Cylinder #3 misfire. I've replaced the coil/sparkplug.....I also swapped the fuel injectors # 1 and # 3. It runs fine for a couple hundred/thousand miles then spits out the P303 again. It's done this 3 times in 2 years. Just recently I put an analyzer on it and with no errors or CEL I get an STFT B1 S2 and B2 S2 both running at 99%. STFT B1 S1 and STFT B2 S1 both running less than 1% at idle. Anyone have any ideas?

 

Nothing wrong with those STSF readings.

I'd be thinking an intermittent in the harness or connectors to the #3 coil or injector.

"Wiggle test" time.

Good luck.

Steve