Are you getting a lean code P0171 on your 3800? (Page 1/1) yamaha94 AUG 11, 04:22 PM This lean code was a tricky issue to tackle: I thought I share my experience with it here. I had High Long term fuel trims and High short term fuel trims were the culprit for me - I had approximately 16.4 Long term 15-20 for the Short Term...creates a code on driving not on idle. I investigated that it could possibly be a fuel or air leak. Digging further I removed the EGR. Cracked under the lip on the LIM side and at the exhaust manifold side...deleted with block off plates and in the software so the EGR would not be activated. One problem fixed. Problem still remained...changed the injector seals....MAF sensor, PCV valve and IAC sensor. Small improvements in the Long term and short term fuel trims. Not done yet. What else could it be? i hear a hiss coming from the Charcoal cannister. I made one small mistake with my setup....I do not have a EVAP solenoid in between the canister and the throttle body nipple to the EVAP. Basically - I have a hose going from the throttle body to the EVAP, split to both connections. This setup was causing a negative fuel pressure issue thus being a big part in my fuel trim issues. The solution: (Which many people probably have, or have considered) - Cap off the throttle body nipple to the EVAP with a vac delete cap. And run a hose from the EVAP cannister to atmosphere. Code gone. Problem solved. Almost instantly - Long fuel trims went back to normal range 0 - 2% and short term between -1 and +2%. Take care!