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Gas Mileage "To-Do" List

S

shawnmahmud

NAXJA Forum User
Location
Minneapolis, MN
My to-do list for a '98 XJ (150,000 miles) getting about 12mpg (down from 17mpg a year ago):

- new catalytic converter (original, sometimes smells like sulfur which I've heard means moisture inside)
- new #1 Oxygen sensor
- fuel system cleaner
- change rear diff (chrysler 8.25") fluid and refill with 75-140W synthetic (live in MN and local dealer says it improves mileage in low temps)
- clean out CCV tubing b/c I have oil residue coming out the valve cover at the attachment that runs into the air filter box
- already put in new air filter with no improvement; tires are properly inflated

Suggest additions/deletions?...my budget for this can't go much past $250 right now. Cap/rotor/plugs/wires replaced 2 years ago (~40,000 miles).

Thanks-
 
I'm noticing the same thing with my '92 (215K). I realize that the 2" lift and 30s are affecting me slightly, but it seems too low anyway (think I'm maybe getting 15 on the highway, and I figure I should be getting at least 18 if everything was right.

I'd also consider the computer's coolant temp sensor and thermostat - if the engine doesn't warm up enough to get out of "warm up mode", that's extra fuel being dumped in. A bad sensor will trick the computer.

I dont' get a sulfur smell from my exhaust, but it does smell strangely hot (and I notice when not moving much that I get a good bit of heat transer to the cabin. Of course, in my case, the heat shields on my cat have long since rusted away...

Good luck.

Rob
 
I have replaced the following:

Cap - Dealer
Rotor - Dealer
Spark plug wires - Dealer
Coolant temp sensor - Dealer
Thermostat - Dealer
Distributor - Dealer
Front O2 sensor - Napa part
Fuel rail and injector cleaning
Can of GM Top End Cleaner
Fuel Filter - Napa Gold
All boxes serviced less than 2k miles ago
New Air Filter
I have reset the computer multiple times

I was getting about 12MPG City, 13 or 14 MPG highway

Then I lifted 5.5", slapped some 33" MTs on there, and then regeared to 4:56 (auto trans). Now I get 10MPG combined city/highway.

WTF would cause such crappy mileage? I don't think 14 or even 15mpg would be an unreasonable thing to expect from my Jeep.
 
Xj's suck on gas. There aint much u can do about it besides drive like a grandma on her way to church. I even think the new dodge ram hemi gets better gas mileage then a 4.0L xj.
 
CToyeIV said:
Something around 10 sounds right for a lifted Jeep, check the OE Specs they say about 12 mpg stock with the L6
Click to expand...


Mine gets 20+ on the highway with 6.5" of lift, 32's and 4.56 gears. Normally I average about 16 though.


I'd replace the cap and rotor again, they are cheap enough.
 
mines alright on gas, i get 25mpg on highway with 2in lift and 31's. its an 89 limited. if its been 2years shawn since a tune up its time. i do mine every 2 years max, just my preferance. also if u can get away with removing ur cat, i would. i know some places in usa check for catylitic convertors. where i live they dont care so i took mine out. some will argue you should keep it in so...up to u
 
have you swapped in the new speedo gear ? that might acount for it , figure your speedo tags to the brainbox some way etc . I figure with 33 BFG MT and 3.55 my speedo is off 55 on the speedo is like 64.8 real time .. so check that maybe maybe not
 
I feel terrible for however has an xj and gets 10 MPG, my 96 sport has original gears with about 3 inch bigger tires and i get around 25 but if you factor in the speedo being off becuase of the big rubber, then its most likly around 20 my father has a 97 grand cherokee and he gets 21 in the city completly stock

also if you have bigger tires the speedo reads higher than actual speed therefor if you havnt changed the speedo gear you would see beter gas milage
 
maine96xj said:
I feel terrible for however has an xj and gets 10 MPG, my 96 sport has original gears with about 3 inch bigger tires and i get around 25 but if you factor in the speedo being off becuase of the big rubber, then its most likly around 20 my father has a 97 grand cherokee and he gets 21 in the city completly stock

also if you have bigger tires the speedo reads higher than actual speed therefor if you havnt changed the speedo gear you would see beter gas milage
Click to expand...

If you have bigger tires, the speedo reads lower than actual speed; therefore if you change the speedo gear, you would see better gas mileage.

That last sentence is completely opposite of what you said in the first paragraph.
 
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