I have never done any evaluation of MBs using OBDII LTFT (I always use the part load and CTP adaptations MB uses). I have done it somewhat with BMW which is basically the same or should be. I just don't exactly know how it applies as MB uses two seapate (or three on later cars) addaptive zones. The concept with addatation is that as STFT or O2 sensor control (as the Germans call it) approaches its limit of correction an adaptive correction is made percentage wise to the base fuel calculation. This sets the O2 sensor control back towards the center of range.

If you note your B1 fuel trim it all takes place about zero. B2 never gets above zero all negative. This means the base calculation is giving too much fuel and O2 sensor control is working to the negative subtracting fuel.

If you cancel LTFT and start driving within five miles you will see a stepped adjustment to a stable position. It could take a mile or two for each step so a graph will look like a straight line unless it has very long time frame capablilites.

Load. RPM or throttle position would be a good tracking point for comparison.


I would suggest only looking at just STFT and LTFT (and one of the above comparators) as O2 sensor voltage is redundant. STFT is the controllers interpretation of O2 sensor anyway. Plus it puts numbers to the relative correction taking place. In other words the amount of time the sensor voltage stays high or low is an expression, harder to see, of how much the system is pulling mixture rich or lean.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician