P0171 and P0174 Codes after Stillen CAI - Help needed

Jazzster · 06-17-2015, 08:00 PM

Ok - I learned a LOT about fuel trims. The Dash Command app along with a wifi OBD dongle from Amazon is amazing. Not only does it read and reset codes, it also logs anything the OBD is seeing and that includes short and long term fuel trims which is what I needed to watch. When I'd drive the car I could tell when it was going to throw a code because my short term fuel trim would be 25 for some time and then dip to 0 causing my RPMs to drop and stumble just a little. My short term fuel trim was 25% at idle meaning the car was running VERY lean. Your trims should be close to zero but can bounce around from 8 to -8 as the ECU compensates and tries to maintain a balanced Air/Fuel ratio. When I would rev the car the STFT would drop back to almost normal levels. At idle, back to 25. Definitely a vacuum leak. So I went back over all my intake piping and discovered the issue - a coupler had slid off of the pipe on the bottom where you couldn't see it and it was on the opposite side I had been looking. I didn't LOOK like it was off and the clamp was tight. But upon feeling all the way around it with my fingers I found it. After adjusting the pipe and re-tightening the clamp all my fuel trims were between 9 and -9 and mostly around zero. I think that was all it was. For some GREAT info on this check these pages out:

Fuel Trim?

P0171 and P0174 - OBD-II Trouble Codes

And get Dash Command if you have an iphone along with a wifi OBDII dongle. It is a great tool and resource.

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06-17-2015, 08:00 PM	#8 (permalink)
Jazzster Base Member Join Date: Nov 2014 Location: Cordova, TN Posts: 28 Drives: 2010 370Z Roadster Rep Power: 11	Ok - I learned a LOT about fuel trims. The Dash Command app along with a wifi OBD dongle from Amazon is amazing. Not only does it read and reset codes, it also logs anything the OBD is seeing and that includes short and long term fuel trims which is what I needed to watch. When I'd drive the car I could tell when it was going to throw a code because my short term fuel trim would be 25 for some time and then dip to 0 causing my RPMs to drop and stumble just a little. My short term fuel trim was 25% at idle meaning the car was running VERY lean. Your trims should be close to zero but can bounce around from 8 to -8 as the ECU compensates and tries to maintain a balanced Air/Fuel ratio. When I would rev the car the STFT would drop back to almost normal levels. At idle, back to 25. Definitely a vacuum leak. So I went back over all my intake piping and discovered the issue - a coupler had slid off of the pipe on the bottom where you couldn't see it and it was on the opposite side I had been looking. I didn't LOOK like it was off and the clamp was tight. But upon feeling all the way around it with my fingers I found it. After adjusting the pipe and re-tightening the clamp all my fuel trims were between 9 and -9 and mostly around zero. I think that was all it was. For some GREAT info on this check these pages out: Fuel Trim? P0171 and P0174 - OBD-II Trouble Codes And get Dash Command if you have an iphone along with a wifi OBDII dongle. It is a great tool and resource.