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MPG 99 XJ 4.0 question

ZoranZ

NAXJA Forum User
Location
Beacon, NY
Alright.. What kind of gas mileage should I be getting with a 4.0 99 XJ with 30's? Average. I did some calculations and came up with an average of 14.5 mpg and that seems a little low. It was a mixture of side roads (no stop and go but 45mph ish) and some highway 75+mph
 
I'm at 2" of lift with 235's.

I average 14.5-15mpg with short trips, city driving in the summer.

On the highway I get just under 20mpg. 65mph is the sweet spot.
 
I'm at 2" of lift with 235's.

I average 14.5-15mpg with short trips, city driving in the summer.

On the highway I get just under 20mpg. 65mph is the sweet spot.

Thanks for the feedback! I have no lift on here yet. A friend suggested swapping out the o2 sensor before the cat.

Probably should add more to this. it's a 99 XJ 4.0 with 203k miles on it. No check engine lights, clean air filter. Not sure what else would really effect gas mileage.
 
Not sure what else would really effect gas mileage.

Other than going 75+ in a vehicle shaped like a brick...

  • Old worn tune-up parts, plugs, wires, cap etc.
  • Some exhaust restriction (cat converter)
  • Larger tires
And anything else that cuts down on the peak efficiency of the engine. If you needed an O2 sensor, your light would be on
 
There are plenty of XJ MPG threads to search. And most will say the same, tune-up, and drive your brick shaped 4x4 slower.

... If you needed an O2 sensor, your light would be on

This is not always true. O2 sensors can get slow to respond and have an effect on the mpg's long before the fail completely and trigger a CEL code.
 
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