[Jukebox]

I just did a full tune up on my 2.4 but my gas mileage hasn't returned completely yet. I just did a 500 mile round trip and only averaged 21.5mpg. I normally get 23 mpg with mixed driving. I recently changed my fuel filter and my air filter, is there anything else that could be affecting it? I did just go from 225/70's to 235/75's, but I don't think that is the problem since it really started before this.

 

[Whiffle]

What was in your tune up? "Tune up" can mean different things to different people.

Other things I can think of (although some of them are pretty unlikely)
tire pressure
correct spark plugs
thermostat (is it running too cold?)
MAF sensor
o2 sensors
clogged cats
slipping transmission
dragging brakes?

 

[Jukebox]

Plugs, wires, cap and rotor.

 

[TheOregonFront]

Plugs, wires, cap and rotor.

how about running seafoam?

 

[ronpozoromo]

Going from a 225/70R15 (approx 27.5" o.d.) to a 235/75R15 (approx 29" o.d.) will affect your speedometer and odometer accuracy. 1 1/2 inches will show your are going slower than before and going fewer miles. Your gas mileage probably won't be that much different if you can figure out how to factor the difference in tire o.d.

 

[Jukebox]

I'd never even heard about it until now. I might try that.

 

[Markcuda]

You went with a bigger tire, and probably a lot heavier tire, you are paying the price of bigger tires.
Weigh the new ones verses the old ones.
Plus, like mentioned earlier, your spedo is now off a bit.

 

[Jukebox]

Thanks guys. I realized my speedo was off but I forgot what affect that would have on my OD. I'm sure I'm just not reading it correctly.

 

[GrnXnham]

Go Here to calculate your difference in speedo with bigger tires.

Tire Size Calculator - tire & wheel plus sizing

 

[1fstmax]

lol same thing happend to my 4banger.. with my 3.70 gear ratio it sucks gas with those 235/75/15 tires..

need to change that gear ratio :/

 

[Whiffle]

Didn't you say your mileage got worse before you got the new tires?

 

[4cylman]

with my 3.70 gear ratio it sucks gas with those 235/75/15 tires..

what gear ratio do u want with this size?