My understanding of the Fuel Trims is as follows:

The ST and LT trims are additive to the injector duty cycle. So, if you have LT of +8 and ST of +2, you are going to get 10% more injector open time. (This I'm NOT sure of, but I think it's how it works).

The LT trim is changed when ST trim stays at an elevated (away from zero absolute value) value for a specified amount of time (not sure how long) at the same engine conditions (MAF, Load, TPS, etc.). The goal of the LT trim is to keep the ST trim near 0 absolute (I think +/- 3 or so).

As far as one bank being much different from the other, my guess is that it could be clogged fuel injectors or intakes, or a dying O2 sensor. But, these are only guesses and I don't have my Service CD handy. I'll try to give you a more complete answer later. Can you give me the exact code you read?

The lean codes fire when LT + ST trims > +30% (i.e. the PCM is at it's wits end trying to add fuel to stay stoich in closed loop). Check the "Freeze Frame" for what was going on exactly when it fired.


1998 Silver Frost SVT Contour born on...8/28/01[/i]
American Iron Shootout Radial Tire 2 Class Champion, Cecil County Dragway April 20, 2002