Got my car together last week after replacing a bad head gasket, now i've got a small vacuum leak in my lower intake gasket(at idle it's at 17:1 afr, and when sprayed with carb clean the idle changes when spraying in that area right behind the dizzy, knew i should of used the cork). While driving it's perfect right at 14.7:1 region, always switching back and fourth. but at wot it's at a stead 12/12.1:1 afr, it used to be right at 13:1. any ideas what would cause this? I'm going to check the timing again but i set it at 14 degrees base, and before it was only at 12. so what's everyone think?

 

actually, with the new E10 ethanol blended fuels... you'll get better power closer to 12:1

and 14.7:1 was stoich for regular gasoline... E10 burns at 14.08:1

 

wtf? didn't know gas was saposed to change anything that much.

 

amazing, isnt it

 

so was that serious or just a joke? lol, hard to tell with you sometimes.

 

im quite serious

Fuel ___________________AFR

Gasoline stoichiometric_____14.7
Gasoline max power rich ___12.5
Gasoline max power lean___13.23
E10 stoichiometric________14.0 - 14.1
E85 stoichiometric________9.765
E85 max power rich_______6.975
E85 max power lean______8.4687
E100 stoichiometric_______9.0078
E100 max power rich______6.429
E100 max power lean_____7.8

 

so all gas is e10 now?

 

read the pump

 

huh. well that's good to know. but would a vacuum leak cause it? i didn't think so but who knows.

 

tell you what you can do if you don't believe it. Go fill your tank up with some real gasoline one time and check your gas mileage. Then go get the ethanol crap and check it. Guarantee you it will have better gas mileage with the regular gas than the ethanol blend. And oh course no, not all gas is not e10. Most of it but, not all of it.

A vacuum leak will pull in air that is not metered by the maf. Which will cause the car to run lean. If the computer picks up on this, it will give it more fuel and cause it to run rich. Adder can explain it better but, yeah you need to get the leak fixed or you will have problems.