Long Term Fuel Trim Bank 1 drops to 0 at idle, or foot off gas pedal.

[bills4065]

Idle Readings: LTFT1 - negative .8, LTFT2 is 10.9, STFT1 negative .8, STFT2 negative .8 When you push down on the gas pedal driving LTFT1-6.3% LTFT2 is 8.6% STFT1 is 3.1% STFT2 is 4.7% When you let off on gas pedal or sitting with truck in park idling , the Long Term Fuel Trim Bank 1 drops to negative .8 %. Any one ever seen either of the long term fuel trim banks drop to 0 on taking foot off the gas, or sitting idling. 2008 V6 automatic transmission.

 

[franklin2]

On fuel trims I thought zero was perfect, and the further away from zero you got, more likely you have a potential problem. They say in this article I found it usually has to get to 25% before the check engine light will light up.

Long-Term & Short-Term Fuel Trim

Long and short-term fuel trim are very useful indicators of engine performance, This post goes over exactly what they are, and what they tell you.

gtc.ca

 

[bills4065]

@franklin2, great article Thank you for sharing. This is a friends Ranger, he asked me to scan it for him. Long terms Bank 1 and Bank 2 seem to be within specs when driving the vehicle. It is just if you take foot off the gas pedal, or are sitting at idle . Long term Fuel Trim bank 1 drops to negative .8% Long term fuel Trim Bank number 2 stays at around 9%. It seems too me that LTFT bank # 1 is not learning, that is just a guess on my behalf. He sad truck has gotten a lot harder on fuel. I know my own ranger, the LTFTs change , but they are within a couple % of each other.

 

[bills4065]

If anyone is interested, this vehicle would have been too expensive to have rust repairs carried out, would have been more than vehicle value. He did donate it to automotive training campus , were automotive instructor and students used this as training. The instructor did call him and inform him this ranger had a restricted exhaust on bank # 1. Just a note of interest, I contacted the instructor at this trade school. He said they use James Halderman engine diagnostics books for training students. There is a You Tube video on this: Fuel Trim Imbalance case study presented by John Thornton. Gets quite technical in the video.

 

[alwaysFlOoReD]

If anyone is interested, this vehicle would have been too expensive to have rust repairs carried out, would have been more than vehicle value. He did donate it to automotive training campus , were automotive instructor and students used this as training. The instructor did call him and inform him this ranger had a restricted exhaust on bank # 1.

Thanks for the update.