Misfire Help

[C420sailor]

This question doesn't exactly pertain to Explorers, but I trust y'all more than anyone else, and I'm looking for generic troubleshooting wisdom that can benefit the gander...

5.4L 2V in a '98 Expedition
240,000mi, original fuel pump and injectors

Developed a miss under load. Changed the plugs (they were due). Still there. It now misses at idle. Hooked up forscan. P1000 code only. Forscan is detecting intermittent misses. It seems like when the truck is missing, STFT on bank 1 goes to around 20%. Then she'll smooth out and STFT1 drops to about 3%. Then she'll start missing again with the STFT back up. No rhyme or reason, and it's very binary---sudden and complete changes. Smooth as silk to shaking the truck and back. Both bank 1 oxygen sensors correlate with STFT. Bank 2 seems steady and solid as rock, with all data looking great.

So whatever this is, seems to be very isolated to bank 1, and sudden on/off/on/off. If it was both banks, I'd be looking really hard at vacuum leaks.

I'm wondering if an injector is on the fritz. If it was a coil (COP), wouldn't the O2 sensor go rich, and send STFT negative?

What's the best way to confirm and identify a bad injector? I was tempted to disconnect the injectors one at a time and see if the problem got worse or stayed the same, but something in the back of my mind was telling me that I would mess something up.

What do y'all think?

 

[Mbrooks420]

You can unplug the injectors while running. I’d suspect them. At this age it’s almost just time to change them out.

 

[C420sailor]

Checked for vacuum leaks. Pre emptively changed some hoses. Passed smoke test. Changed the PCV for good measure.

Noticed that if I unplugged the injector on one particular cylinder on the trouble bank, the misfire waveform in Forscan smoothed out—no misfires. If I disconnected any other injector, the misfire waveform remained. I took this as the problem being on that cylinder. Forscan will not identify which cylinder is misfiring. It gives me total misfire count only. For all the hype, this software kinda sucks.

Swapped out the coil. No difference.

It could be the injector, but I think I’m done throwing parts at the problem, and I don’t need the stress and time wasted. I think I’m going to retire this vehicle to the great junkyard in the sky.

I’ve overall found the 5.4 Triton to be a garbage engine. Starting at relatively low mileage, nothing but problems. Vacuum leak after vacuum leak after vacuum leak. P0171/0174 codes with no leaks found. Shop can’t find leaks either. We luckily had a guy who would just pass the inspection with the CEL on. Plugs are a ***** to get to. It eats COP coils. Passenger side exhaust manifolds? It rots those out every 5 years.

Junk.