RocketMouse

I know... I know... before the flaming starts about the words MPG and Jeep being mentioned in the same sentence. lol....

The XJ's in pretty good nic overall. When I was living at approx. 5,000 ft. above sea level, I was averaging between 15-17 mpg in-town on the standard crap winter blend.
I just recently moved to a place where I'm now at just over 7,000 ft. and on the same octane crap winter blend, in nearly identical driving conditions in-town, I'm averaging 12-13 mpg.
The Jeep still seems to run well, and mechanically unchanged from my previous location.
So my question is.... does a 2k in altitude increase cause that much of a difference in the AFR? And any ideas on if it's possible to adjust it for the new higher altitude?
And small side note.... on the move to my new location I rolled right around 70 mph (give or take a hair) the whole way and averaged 19-22 mpg on the highway. Which I thought was quite good for a 19 yr old 4 litre 6.
Thanks!

StealthyMcStealth

I have done some reading on this and our older Jeeps are different than modern vehicles. Basically the thinner air makes it run rich and the computer isn't smart enough to correct the AFR. That is a way over simplification but basically says what could be happening.

Or... it could be that your new area has a couple more uphill climbs, or a few more long red lights, stuff like that can change your mileage too.

The only fix that I know of is an aftermarket engine management system, which is pricey.

craigjacob1

Pretty much.
Since you have a 99 you could probably get the modification you need from a performance chip.
I haven't done any research on chips because I'm running a renix ecu.

$200 - $600 seems to be the price range.
If it does give you 4+MPG it will pay for its self in a few months (depending on driving habits).

cruiser54

It's not the AFR. It's lack of air.

There is a loss of horsepower as you go up in altitude and I would think a loss in fuel economy also. Lower compression....

s346k

educate yourself on density altitude. same reason drag cars suffer in high da situations. the air is less dense resulting in less power. natures way of making an na engine be far less efficient from end to end.

cruiser54

That's the term I couldn't remember earlier this morning!!!