[mwebb]

although the system should be at stoich
fuel trims will be subtracting
and
more important , timing WILL be retarded which will results in INcomplete combustion with will add more combustibles to the exhaust stream

which will make the fuel trim issue even worse
========================
on speed density system
a vacuum leak
will
lower intake vacuum = higher load value = less timing and more fuel
it will never make the system lean

Originally Posted by dcb

Correction, it will result in a stoichiometric condition as long as the system can compensate for the additional air via the o2 sensor (and updates the trim values, etc). Coyote and others have noted that their cars are basically "pegged" on the "try to add more fuel" side on e10 as the ecu tries to bring the mixture back to stoic (14.2 ish for e10). Once at the limit of the system to compensate, any additional bypass air means leanness.

Though their spark plugs should be pretty clean if they are constantly lean.

It may also be a function of "driving on the o2 sensor", i.e. the internal maps are targeting 14.7 for the fuel schedule and the o2 compensation algorithm just kinda sucks when you get to 14.2 (large mixture "ripple")


EDIT: Nery's what fuel injections system(s) do your cars employ, all TBI by any chance?