I have a 99 camaro m6 with cold air, 4.11 gear 160 thermostats ,no change in mpg when changing to 4.11gears ,changed fuel filter still the same & cleaned maf & also seafoamed it still the same ,do you think it could be the thermostats ,the car run good ,but only gets about 9-10 mpg

 

plugs? and did you clean the maf before or after you noticed the poor fuel economy?

 

It could be the O2 sensors. Every time my car randomly gets bad MPG I take it to auto-zone and plug the scanner in. Also you might want to check your plugs if it isn't O2

 

didn't think to mention the O2s, good call. those can definitely kill mpg when they go bad. how many miles on the O2s?

 

before I cleaned maf, o2s have about 10k on them

 

4.11 gears should hurt your MPG, not help. Thermostat shouldn't make any difference positive or negative. Only mod it seems you have that should help is the after market filter/induction.

Generally MPG is about how you drive, not the car. Any type of spirited driving will kill your average.

 

How did you clean the MAF? Theres a chance you screwed up some of the wire sensors within that are screwing with you a/f ratio. Or it could just be a combination of the gears with needed a tune up (filters/plugs/wires/etc) B/c as stoleit said going with a higher ratio gear will hurt your MPG's if your driving habbits remain the same (although usually after people mod cars they tend to push it harder, which is why we mod them, to make them faster). Only way the gears will hurt the MPG's is if you lower the ratio

 

i have 4.10's and a cam and i still get 25 highway soo it cant be the gears doing that

 

LOL gears are not the problem i have a bolt on m6 with a 9" and 4.11s and i get 30mpg down the freeway. i would put money on the maf or o2s

 

^ Another thing to consider is you dont know what kinda driving he is doing getting 9-10 MPG. My old cam F-body M6 still got great highway MPG but it hurt my city driving, especially b/c I beat on it more. Although there is a good chance the MAF or o2s can be causing the problem, I wouldnt rule the gears out for some effect yet until we know all the info

 

A/f 14.0,14.5 on the highway,is there anything in the tune i need to look at