jpmason33

Could someone explain over fueling, its cause? The problems it creates? The Benefits? The fix?

Cheers


James

nom

!
Quite a question
Overfueling - erm, too much fuel The engine needs a different AFR for different loads (as standard - with a cat - 14.7:1 on cruise, going up to 10.5:1ish on full boost).
It's cause - many! Typically, if overfuleing on cruise, it's usually because the lambda sensor is old & misreading (note that if the lambda sensor is misreading, so is any gauge attached to it!). On boost, the lambda sensor isn't used, so doesn't cause the problem; the standard ECU massively overfuels on boost, though.
The problems - too much fuel dilutes the oil, so the oil stops working properly over time. Bad economy. Loss of power.
The benefits - the only one that is useful is the fact that fuel can act as a combustion chamber coolant - this is why the standard ECU overfuels so much - it's much 'safer' to run this way. 10.5:1 is far too rich for these engines - 11.5:1 or so (a big difference, by the way!) is a good safe point at full boost, tapering towards 14.7:1 on cruise with a cat, or 15.5:1 without.
The fix? Depends on which particular problem!

jpmason33

THX for that