fast240z
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- Dec 13, 2007
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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:
Driving at cruising speed -
After exiting freeway and sitting at idle:
WOT in 4th gear-
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
Driving at cruising speed -
After exiting freeway and sitting at idle:
WOT in 4th gear-
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