P0171: LT fuel trim high but ST looks good
I have a nagging P0171. No SES light but the code is there. I haven't had it inspected because two shops have told me it won't pass inspection with a code, even if no SES light.
Originally had high STFT values. Replaced bad vacuum hose. Found vac leak at supercharger gasket; tightening s/c bolts seems to have resolved that. STFT went to about zero and I thought my issue would resolve. No dice.
Live data while driving shows the short-term fuel trim hovering around zero but the long-term fuel trim is +13 to +16. Even after resetting the fuel trim, the LTFT increases back to +16 in short order. The engine is running fine: no concerns with acceleration, fairly smooth idle. I took it for an hour drive with my son watching the live data. Event LTFT looked good most of the time; would jump up if I accelerated hard. It appears LTFT goes up at idle.
Cleaned MAF with Mass Air Flow Sensor Cleaner spray.
Fuel pressure is 40psi but drops quickly. I think that's because there's a leak at a swivel connection with the gauge rather than a problem with fuel supply. (If I disconnect gauge, charge it, I get a good squirt when opening the Schrader valve.)
Disconnecting MAF sensor does not clear P0171 - just adds P0102.
I'm at a loss on how to proceed other than to methodically progress through service manual steps with possibility of replacing upper end gaskets, more hoses, etc. Suggestions greatly appreciated.
Originally had high STFT values. Replaced bad vacuum hose. Found vac leak at supercharger gasket; tightening s/c bolts seems to have resolved that. STFT went to about zero and I thought my issue would resolve. No dice.
Live data while driving shows the short-term fuel trim hovering around zero but the long-term fuel trim is +13 to +16. Even after resetting the fuel trim, the LTFT increases back to +16 in short order. The engine is running fine: no concerns with acceleration, fairly smooth idle. I took it for an hour drive with my son watching the live data. Event LTFT looked good most of the time; would jump up if I accelerated hard. It appears LTFT goes up at idle.
Cleaned MAF with Mass Air Flow Sensor Cleaner spray.
Fuel pressure is 40psi but drops quickly. I think that's because there's a leak at a swivel connection with the gauge rather than a problem with fuel supply. (If I disconnect gauge, charge it, I get a good squirt when opening the Schrader valve.)
Disconnecting MAF sensor does not clear P0171 - just adds P0102.
I'm at a loss on how to proceed other than to methodically progress through service manual steps with possibility of replacing upper end gaskets, more hoses, etc. Suggestions greatly appreciated.