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Hi everyone, i have negative long term fuel trims (around -10%) for both banks while idling and while running with the foot off the pedal. While driving normally ltft and stft are in normal ranges. No DTCs present, O2 sensor readings seem ok. Any suggestions?
Thank you
so running a little rich only at idle,i wonder if fuel pressure regulator diaphram has small leak?does this vehicle use pressure regulator that has a vacuum line to it?
maybe try looking at your fuel trims and pinching the evap line and see if fuel trims go normal
Yes indeed it has a pulsation damper (this is a returnless system vehicle, so i guess the regulator is with the fuel pump) which is connected to the vacuum line. Disconnected the vacuum, no visible leaks or traces of fuel. When you say pinching tha evap line you mean the hose from the intake to the purge valve?
Thank you
Are you talking LTFT, STFT, total trim?
To perfectly honest, if the computer isn't concerned enough to set any trouble codes, I wouldn't spend any time or money on it.
Unless there is a running complaint or engine light, I wouldn't go chasing it at this point beyond maybe an oil change and keep alive memory rest.
It's possible for fuel contaminated oil to cause richer than normal trims via the pcv system. You can try cleaning the MAF to see if there's an improvement, or as boosted suggested, isolating the evap system, but like I said, if this came to me, I would probably ship it and move on to next car until there is a more tangible issue.
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