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Working on a 2000 F 150 with a 4.2L. Came in with system lean codes on both banks (P0171 P0174). Had a vacuum leak which was repaired and I cleared the codes. Well when I was checking the scan data afterwards I noticed that my STFT on both banks was fixed at -20 and my LTFT was fixed at 15. It did get better as rpm was increased but what threw me off was that my down stream O2s were fixed rich. The did react with snap throttle tests and was able to drive them lean but didn't know what the next step would be. Any thoughts?
if your LTFT dose not seem to be releasing, disconnect the battery and connect a non led test light between the leads for like 10min. see then what the trim dose after a cleared memory.
randy.martin wrote: Working on a 2000 F 150 with a 4.2L. Came in with system lean codes on both banks (P0171 P0174). Had a vacuum leak which was repaired and I cleared the codes. Well when I was checking the scan data afterwards I noticed that my STFT on both banks was fixed at -20 and my LTFT was fixed at 15. It did get better as rpm was increased but what threw me off was that my down stream O2s were fixed rich. The did react with snap throttle tests and was able to drive them lean but didn't know what the next step would be. Any thoughts?
Your good man. Ford's are goofy with relearning the LTFT. It does not happen right away and driving the truck is necessary. Just reset your KAM through the scan tool or do a "cap discharge" (disconnect battery and touch terminals together)
randy.martin wrote: Working on a 2000 F 150 with a 4.2L. Came in with system lean codes on both banks (P0171 P0174). Had a vacuum leak which was repaired and I cleared the codes. Well when I was checking the scan data afterwards I noticed that my STFT on both banks was fixed at -20 and my LTFT was fixed at 15. It did get better as rpm was increased but what threw me off was that my down stream O2s were fixed rich. The did react with snap throttle tests and was able to drive them lean but didn't know what the next step would be. Any thoughts?
I'm with the others, a KAM reset is in order to fix the fuel trims. Fords are very picky about when/how the learn long term trims; Toyota is the only other make I know that's more stubborn.
As for the downstream O2's, maybe the catalytic converters are just working that well? I'd say if the sensors start out at 0mv and climb up as the engine warms, then you're probably good to go.
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