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I have a 2015 Ford Focus SE, 2.0L Duratec, at roughtly 160k miles that is showing a P0172 code. I’m new to diagnosing with scan tools so I have no clue about this stuff for the most part.
At idle my O2 sensors are showing a true rich condition and I know they’re accurate. My MAF sensor is reading between 2.8 - 3.5 g/s but my STFT is at -4 to -5 and my LTFT is at -25 (which I just assume is the max allowed)
at first I considered a vacuum leak because of the fuel trims but I sprayed it down and couldn’t hear or see anything and also my STFT sits at about 1-2 but my long term is still high at -25 and sometimes drops to -23 if I’m lucky
(Also doing the MAF unplug test doesn’t do much for me, everything is the same pretty much)
if anyone needs more details or knows how to lead me in the right direction just let me know. Thanks!
You won't need to worry about vacuum leaks for this fault on a MAF system, as a vacuum leak will cause a lean condition, and you're too rich.
The MAF is reading you mentioned of 2.8-3.5 g/s could be high, and would match a rich condition. Would you mind looking at the MAF g/s again? Engine fully warmed up, at idle, no accessories or loads on (A/C, heater, radio, headlights, like that).
Another potential source of a rich condition would be a stuck open purge valve. Normally there's other faults that come with a stuck open purge on these vehicles, but still worth checking. Just disconnect the purge valve at either the intake or the vapor line and recheck your trims. If they're the same, connect the purge back up and move on. If they're night and day better, you might be onto something.
