Help me out with some math
 

I'm having trouble increasing the FE of my Protege, and I think I may have found part of the reason why. Driving home just now, I was on a street doing 40mph with the cruise control set. Level ground, and my FE was 33.4mpg. I used the cruise control to accelerate a bit. Monitoring my SGII, I saw the FE drop from 33.4 to 17.4 during the acceleration. Roughly half.

The math: Half the FE means twice the fuel, right? Assuming a steady-state fuel mixture of 14.7:1, doubling the fuel would richen the mixture to approximately 7.35:1. That's incredibly rich. Enrichment shouldn't drop the mixture much below 12:1. Forced-induction setups can sometimes require richer mixtures, but not a street-tuned normally aspirated engine.

Thoughts?

The mixture stays roughly the same, you're just using twice as much fuel and air since you're accelerating.

It takes work to accelerate your car - and the work is powered by burning more gas AND air in your cylinders.

Proteges have street racer gearing... at least my mother's 2L 4A does... fun car though, but thirsty.

accelerating with cruise control not good
 

Lot of cruise controls will basically floor the gas pedal to accelerate. And flooring it is about the worst thing for FE. Do the acceleration yourself, slowly, then set the cruise control at the new speed when you get there.

Hmm all the CC's I have used have always accelerated slower then me. Guess its all the time at the drag strip coming through.:D :D

The Pro's are awsome cars though!! I work for Mazda, and frankly there one of the best cars out there!!!

:p Parts for my 626 didn't cost much :thumbup:

Ya know, I feel kinda dumb right now. Of course it's extra air.

Oy, last week was a tiring one. Posting this was the second brain-dead thing I did on Friday.