AJ16 Engine Facelift LTFT
#1
10-04-2017, 09:33 AM
#2
10-04-2017, 10:09 AM
LTFT and STFT are percentages which represent the adjustment to the fuel injector pulse width. The LTFT and STFT are added together, so a LTFT of 10% and a STFT of -5% will equal 5%. A total fuel trim of 10% will increase fuel delivery with 10% and a total fuel trim of -10% will decrease the fuel delivery with 10%. If any of the value exceed 25% or beneath -25% then the check engine light is turned on with a number of error codes, which can be read using an appropriate scan tool.
TFT and STFT will usually stay close to 0%, which equates to no adjustment. However as the engine wears, the adjustment will be necessary. A significant increase in STFT or LTFT from 0% means the ECU is detecting more air than expected and is adjusting fuel delivery with more fuel. A significant decrease in STFT or LTFT from 0% means the ECU is detecting less air than expected and is adjusting fuel delivery with less fuel.
TFT and STFT will usually stay close to 0%, which equates to no adjustment. However as the engine wears, the adjustment will be necessary. A significant increase in STFT or LTFT from 0% means the ECU is detecting more air than expected and is adjusting fuel delivery with more fuel. A significant decrease in STFT or LTFT from 0% means the ECU is detecting less air than expected and is adjusting fuel delivery with less fuel.
Last edited by Keesh; 10-04-2017 at 10:14 AM.
#3
10-04-2017, 10:13 AM
#4
08-17-2018, 04:06 PM
Finally got to the bottom of this!
After driving for too long of a time with the LTFT at 10.something, it was the TPS that was the root of the problem!
The car drove fine, it just had really bad fuel mileage. No check engine lights, no smoke, not really any other symptom, other than poor fuel economy.
I replaced the TPS, with a brand new one, a week ago and my LTFT is at 0.0! I had a spare old TPS that I inherited as part of a used bin of XJS parts and it did not help. I will take this TPS apart and see whats doing.
I do want to note that the new OEM TPS no longer carries the Ford branding that the original parts bore. Also they come with silver pozi screws, instead of brass torx screws. The plate that holds them in also is silver in color, not the old brass color. Thought I would mention that. It was purchased directly from JDHT.
After driving for too long of a time with the LTFT at 10.something, it was the TPS that was the root of the problem!
The car drove fine, it just had really bad fuel mileage. No check engine lights, no smoke, not really any other symptom, other than poor fuel economy.
I replaced the TPS, with a brand new one, a week ago and my LTFT is at 0.0! I had a spare old TPS that I inherited as part of a used bin of XJS parts and it did not help. I will take this TPS apart and see whats doing.
I do want to note that the new OEM TPS no longer carries the Ford branding that the original parts bore. Also they come with silver pozi screws, instead of brass torx screws. The plate that holds them in also is silver in color, not the old brass color. Thought I would mention that. It was purchased directly from JDHT.
