8-9 mpg is way too low Help!

[red87cherokee]

You went to 31" tires and have stock gearing. While the not the largest tire by any stretch, without the regear you will still see a decrease in MPG. That is another contributing factor to your problem.

Tom

Good point; gearing does make a big difference. I have regeared to 4.88's (from 3.07's) in anticipation of installing 35's that I already have. I haven't made the necessary modifications for the 35's yet, so I am still traveling on the 31's. Everyone worries about having too low a gearing and hurting MPG's - 31's and 4.88's get about 2 MPG better mileage than did the stock gears (3.07's) and 31's.

 

[Kejtar]

Good point; gearing does make a big difference. I have regeared to 4.88's (from 3.07's) in anticipation of installing 35's that I already have. I haven't made the necessary modifications for the 35's yet, so I am still traveling on the 31's. Everyone worries about having too low a gearing and hurting MPG's - 31's and 4.88's get about 2 MPG better mileage than did the stock gears (3.07's) and 31's.

So what mpg did you get with 4.88's and 31's? Cause I get around 12mpg.

 

[red87cherokee]

So what mpg did you get with 4.88's and 31's? Cause I get around 12mpg.

On the highway, about 16 (sometimes 17) MPG. You should understand, however, that the maximum speed in Oregon is 65 MPH on the freeways and 55 on secondary roads, and I'm too old to speed like I used to . . . so, these numbers are for a pretty steady 60 MPH on secondary roads - freeway speeds of 70 are not that different MPG-wise, however.

 

[Kejtar]

On the highway, about 16 (sometimes 17) MPG. You should understand, however, that the maximum speed in Oregon is 65 MPH on the freeways and 55 on secondary roads, and I'm too old to speed like I used to . . . so, these numbers are for a pretty steady 60 MPH on secondary roads - freeway speeds of 70 are not that different MPG-wise, however.

Crap.... I think I might have to do some poking around and see what's killing my mpg. I saw some weird dips in the fuel efficiency before I did the gears so it's probably not gear related but maybe O2 sensor or something like that.... oh well, along those lines: if I had bad 02 sensors would I get bad scores on the smog check? Cause my xj passed with flying colors (just looking for a starting point to see what might be wrong)