[Damaso]

Hey guys i put a post about High short term fuel trims (~28%) on my 03 gt. This happened soon after replacing my upper plenum and cai. Well i did some digging and found out that after removing vaccum to the fuel rail pressure sensor they dropped to normal. I also did a resistance and voltage test on the sensor and everything was to spec exactly. After using a vaccum pump on the fuel pressure sensor I found out it was slowly loosing vaccum. What originally caused me to do the tests were a slightly choppy idle and bucking at W.O.T. Any help would be awesome.

[GP-SE]

Did you check to make sure you have no vacuum leaks?

[Damaso]

yeah checked all of the lines and they are good. The only way the SFT's go to normal is when i disconnect the vaccum line going to the fuel pressure sensor and plug the line with my finger

[bulloch27]

Since you changed the upper plenum it sounds as if you have a vacuum leak. Short term fuel trim is adjusted either positive or negative depending on the inputs from Bank 1 & 2 upstream O2 sensors (typically listed as 1x1 and 2x1). A vacuum leak at the base of the newly replaced plenum will show the O2s the engine is running lean and increase the short term fuel trim to balance the AFR.

[Damaso]

Yeah i already know i have a vacuum leak. I already said i tracked the leak to the Fuel Pressure sensor on sensor. STFT's dropped to normal when i unplugged and plugged with finger at #1, so i traced the leak to #2, because out of the 3 vacuum wires only that one brings the STFT's down. When i used a vacuum pump at #2 the Vacuum doesn't hold it slowly drops. The pic isnt my car btw



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