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Just looking to have a little discussion on how the trims impact fuel economy.
If you have a vacuum leak, the engine is running lean, and additional fuel is added to keep the mixture happy. That extra fuel added must impact mpgs at least a little bit. I don't know if the total trims is, say 18%, that means you are using 18% more fuel or not though.
If you are at WOT and have a lean condition, I would think that it would impact performance since the car would likely be in open loop and not getting the amount of fuel it is normally expecting, with no trimming happening. Hence, why you look at O2 voltage for the WOT fuel delivery test.
there is no general rule. As so often - it all depends!
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You might have extremly positive fuel trims and yet normal fuel economy.
Just figure a fuel delivery issue where the trims have to compensate low pressure or clogged filter,clogged injectors....
In this scenario you could still have normal power, normal MPG, and just high trim numbers, eventually that high it turns the MIL on with a P0171/P0174.
Evidently, there are other scenarios.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
At WOT the engine has to run rich just to deliver the requested power and/or torque.
So the actual A/F ratio might be 13:1 and even richer. You look at the O2 sensor just to make sure that the fuel system is capable of providing that rich of a mixture.
An expert is someone who knows each time more on each time less, until he finally knows absolutely everything about absolutely nothing.
we need to keep in mind the most efficient a fuel trim can be is 14.7 psi other than that we are getting into fuel delivery system perameters and fuel injection type above that the computer must pulse width modulate every injection based on other factors I guess the most efficient system would probably be gas direct injection scanner danner has some good videoos explaining how the computer uses long and short trim and how you may be looking at a lie if the o2 sensor is lying based on other factors to correct fuel trim we must deal with those other factors first
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