I have a 2000 3.0L FFV that is having high negative long term fuel trims at idle, and I'm not sure what to troubleshoot next. The trims stabilize around -8 LTFT/+2 STFT when driving, but will spike to -15 after pulling off the freeway and idling.
I bought the truck 5 years ago and discovered it was misfiring badly due to low compression from bad valve seats (common 3.0 issue). A rebuilt set of heads fixed the issue and the truck ran fine. Last year, the heater hose coupling failed and I lost all coolant and warped the heads. I resurfaced the heads and truck has been running fine once again. Recently it started running a little rough at idle and I'm trying to track down the root cause.
I've performed the following troubleshooting items:
- New O2 sensors - both upstream and downstream. Originals were very slow to update and were biased rich.
- New idle air control valve
- Fuel pressure test from fuel rail - 59 psi KOER, 50 psi KOEO. Pressure would hold with key on but would immediately leak down after turning key off. Fuel trims/O2 showed very rich on both banks, and replacement injectors fixed leakdown.
- New injectors - old ones failed leakdown, cleaning didn't fix issue.
- Smoke test on intake - smoke leaked from EGR valve, replaced EGR. No other leaks found.
- New Intake air temp sensor - original was stuck hot
- New coil pack, plugs, and motorcraft wires - original plugs were toast and old coil pack had cracks in it
- Replacement MAF from Autozone - original looked slightly burnt and BARO value was slow to update
The only other issue I can think of is maybe plugged exhaust. The misfire and leaking injectors make me suspect the catalytic converters are plugged, but the truck accelerates to redline fine.
Driving at cruising speed -
View attachment 58496
After exiting freeway and sitting at idle:
View attachment 58497
WOT in 4th gear-
View attachment 58498