Thanks - From the Sept 2006 issue of Motor Magazine there is a great article on fuel trim. I had my Acutron on continuous read and when my MAF error code came in, it locked in the other readings. With both being VERY negative, it would appear the engine was trying to lean out…a lot. Not sure why…too much fuel pressure?
From the Motor article:
Short-term fuel trim
(STFT) and long-term fuel trim (LTFT)
are expressed as a percentage, and the
ideal range should be within 5%.
Positive fuel trim percentages indicate
that the powertrain control module
(PCM) is attempting to richen the
fuel mixture, to compensate for a perceived
lean condition. Negative fuel
trim percentages indicate the PCM is
attempting to lean out the fuel mixture,
to compensate for a perceived
rich condition. STFT and LTFT percentages
are the adjustments made by
the PCM to maintain the 14.7:1 ratio.
No matter what the driveability issue
happens to be, the fuel trim window
should be used first to check the
STFT and LTFT parameters