Some people say you want slightly negative, some say slightly positive (although sometimes it sounds like these people have things mixed up and really want negative LTFT). What is the real effect of having a negative or positive LTFT?

 

My averages for LTFT are around +6.8 but I'm getting an average of 27 degrees of timing with NO knock retard and 02 readings of .89-.90 at WOT. To me I don't even bother to get my LTFT readings close to zero cause when I try, my WOT readings end up being super rich (.97 o2) AND I get knock retard.

 

The problem with tuning based on positive l-trims is that the values will not be consistent all the time - so tuning at WOT will not be consistent either - making wideband tuning pretty pointless.

Chris

 

If you want your WOT tuning to be consistent you need to get your l-trims slightly negative (-2 to -6, etc.). You can then adjust your WOT a/f ratio with the PE vs RPM table.

Chris

 

More or less agree with Chris. But here is another way to look at it:

IF - your part throttle LTrims are "+" (lean), and you are rich at WOT, you will need to make your LTrims "-" in order to remove fuel at WOT (lean it out)

IF - your part throttle LTrims are "+" (lean), and you are lean at WOT, you only need to make adjustments to your WOT settings to add fuel at WOT (richen it up)

IF - your part throttle LTrims are "-" (rich), and you are lean at WOT, you will need to make your LTrims "+" in order to add fuel at WOT (richen it up)

IF - your part throttle LTrims are "-" (rich), and you are rich at WOT, you only need to make adjustments to you WOT settings to remove fuel at WOT (lean it out)

Make sense?