Improving 4.0l MPG

bluebrapper14

New member
you should really check into the edge trail jammer kit. Put one on my 01 tj when i had it, awesome!! I bought the complete kit (CAI, throttle body, and programmer). I am usually weary about the actual gains cold air intakes and exhausts, never been able tell much of a difference, but that is not the case with this kit. the programmer is what really did the trick, seems to bring the engine up to date. much more responsive, and the power gains were impressive. and more importantly.. 3-4 mpg increase for me. Tested multiple times for accuracy becasue honestly i could not believe it ha. The increase in power allowed me not to have to shift down as much on inclines, and overall it seemed like the engine did not have to work as hard to pull the jeep around, which I think was the reason for the mpg gains. overall, well worth the money for me

http://www.rockcrawler.com/techreports/edge_trailjammer_tj/page2.asp
 

chp-sk8

Adventurer
my 2 cents

Had a lifted lock and built XJ on 35's with skids front to back...thing wasa Tank! But I put 4.88's in it as it has an Auto in it and the OD was really tall. I was able to sqeeze 16mpg out of it. I just finished my 89 MJ long arm, 35's skids, cage, built as well, and I decided to go 4.56 as I am running an AX5 tranny. I can only get 14mpg. I will have tell you I consistantly get another 2-2.5mpg by running asitone with my fuel. I only see the benifite in my older vehicals. It takes all of the static pressure out of the fuel and it sprays and burns cleaner.
Just buy some skinnys run those everyday....you have some tall gears in your rig....when you start throwing wt in and on you jeep...you miliage will degrade quick.
 

bldeagle10

Explorer
Had a lifted lock and built XJ on 35's with skids front to back...thing wasa Tank! But I put 4.88's in it as it has an Auto in it and the OD was really tall. I was able to sqeeze 16mpg out of it. I just finished my 89 MJ long arm, 35's skids, cage, built as well, and I decided to go 4.56 as I am running an AX5 tranny. I can only get 14mpg. I will have tell you I consistantly get another 2-2.5mpg by running asitone with my fuel. I only see the benifite in my older vehicals. It takes all of the static pressure out of the fuel and it sprays and burns cleaner.
Just buy some skinnys run those everyday....you have some tall gears in your rig....when you start throwing wt in and on you jeep...you miliage will degrade quick.
never considered acetone...in my 99 with 313k miles i run seafoam and it runs a hulluva lot better but some injector cleaners seem to make the fuel tank to empty just a bit faster...
 

Topgun514

Adventurer
never considered acetone...in my 99 with 313k miles i run seafoam and it runs a hulluva lot better but some injector cleaners seem to make the fuel tank to empty just a bit faster...
Its using more fuel because your injectors were probably clogged and gonna explode soon- not a bad thing to use an extra 1 gallon:victory:
 

bldeagle10

Explorer
Its using more fuel because your injectors were probably clogged and gonna explode soon- not a bad thing to use an extra 1 gallon:victory:
yea that is true. ive always had problems with the stock injectors and misfires. i need to upgrade to the bosch ones soon. and i need to replace the exhaust too :/ its got a few leaks and i think its tellin the ecu im running to lean when i get on the gas causing it to dump way to much fuel and misfire...which means bad MPG's :rolleyes: i inherited the jeep and all its stupid little tedious misc. issues...but i still love it.
 

4X4NDAD

New member
Mpg.

Have you corrected your speedometer gear after your tire size change? Bigger tires roll farther for a complete 360. You are probably getting better mileage than you think. But due to your tire size your not clicking off the miles accurately. My 91 cherokee fully loaded with exhaust, header and intake got 16.6mpg with stock gears 5 inchs of lift and 31s, after I changed the speedo gear. Varified before n after with my gps. Was figuring about 11.8mpg before the gear was swapped out. And it was nice to not have to do the math to figure out how fast I was driving.
 

Jmetsdad

New member
Better MPG

I put vents in the hood toward the back to get rid of the heat, I run only electric fans( removed the clutch fan), one on at 200 and one on at 210, Installed a snorkel and removed the flow reducer in the throttle body feed tube just outside of the air filter lid. No hard acceleration and I get 22 Hwy and 18.6 stop and go. I get about 30% more when I run my HHO setup.
 

mmp3823

Observer
You resurrected quite an old thread. Interesting discussion though. I do need to re-gear my XJ to accommodate for the bigger tires.
 

TylerA23

New member
Good read as I’m looking for the same answer for my stock ‘98. Did the tune up, all the fluids, and still getting ~14. Gonna do the O2 sensors and injectors next.
 

pittsburgh

tacocat
This is an interesting thread, if I could squeeze even 18MPG out of my 2005 LJ I would be thrilled. It got 20'ish when it was bone stock on 30's, then I put it on 33x10.5x15 BFG MT's and it dropped to 12-16 mpg's. Now it is on 31's and it barely does better than 14 mixed city/highway. I once squeezed 20 out of it driving across country in non stop traffic for 100 miles at 50MPH lol.

I might have to look into injectors and maybe a hub kit. I know a lot of people don't think hubs are worth it but my old CJ would loose 2-3 MPGs by driving around with the hubs locked in, even my Samurai would take a big hit on MPGs with the hub locked in.
 

Grenadiers

Adventurer
Jeeps are big Zesta cracker boxes going down the highway. Our built LJ on 35's, running 4.88 gears, gets 15mpg, but, it's mostly an occasional go to town for smokes, and weekend wheeling warrior. Not a daily driver.
 

Happy Joe

Apprentice Geezer
...Trying to remember what I did to the last 4.0 HO to get better mileage - old XJ ('91);
keep the intake filter clean.
removed the intake air restrictor between the filter box and the throttle body (nor sure it did anything but make it noisier).
Ran excessive pressure in the tires (REALLY poor off road performance and wore out the centers of the tires quickly).
Ran the right tire diameter for the axle gears (narrower gives better mileage) (3.07-3.08 gears ran best with around 24 inch diameter tires)
Used the high altitude crank position sensor (think they may no longer be available/are obsolete).
Advanced the distributor to match required some trimming of the hold down bracket.
Used an MSD-6 and BlueMax wires (leftover racing stuff), Helped keep it running better when crawling obstacles improved mileage slightly.
Only use distributor caps with brass terminals (they corrode slower).
Moved the air temperature sensor from the intake manifold to the plastic duct.
Modified the manifold pressure sensor electronics to make it adjustable.
If I recall correctly it never did get to the same mileage as the old stock 4.0 L Ford ranger (24mpg)
Over the years I have tried removing the catalytic converters; never made any difference, always put them back on to sell the vehicle (hassle).
Larger exhaust high flow mufflers and high flow converters usually improves the mileage some but usually not worth the effort & expense... if doing it for maintenance I use 2.5 - 2.75 inch exhaust, whichever is handy & fits, and turbo mufflers (cheap verify the mufflers do not neck down/restrict inside) along with high flow cats for 6 cylinders.
Converted from unit bearings in a Ford pickup to manual hubs - not worth the effort & expense.

Enjoy!
 
Last edited:

WyoCherokee

Adventurer
Having had 3 Xj's and an MJ all with the 4.0. There isnt a ton you can do, as much of the mileage comes from driving style. Best mileage "modification" i have found for all 3 xj's is to get rid of anything on the roof. Ditch huge roof baskets, tires and racks. Those easily will kill 3 to 5 mpg. Keep it under 70 MPH. make sure your AW4 has good fresh fluid and a clean filter. Run the lightest/most durable tire you can. the AW4 is a mileage killer and heavy tires dont help the situation. Aside from a good tune-up, basic copper plugs, clean injectors, and a free flowing exhaust, you just have to expect that you are not going to get 18 to 20 MPG out of an XJ set up to Overland. In stock form, or close to stock form, you can expect 19-21, but as soon as you start adding weight and drag resistant to a rolling box.....well you get it.
 

Happy Joe

Apprentice Geezer
I personally don't blame the not good XJ mileage on aerodynamics; I do admit that CJ, YJs, TJs etc. suffer from areo issues though.
...have (still) a '94 Ford ranger, with a topper; similar size, shape, weight, same size (4.0L) engine (V-6 instead of I-6), same axle gearing both with similarly geared 5 speed transmissions...I think the absolute best mileage the XJ ever got was in the 21-22mpg range; the Ranger (basically worn out) still gets 22 (down from 24-26+, typical highway)...
I blame the not so good XJ mileage on the fuel and advance maps in the computer (not as well engineered)....other than that and the truly excessive weight of the I-6 the vehicles were/are very similar to drive (scrapped the XJ kept the better Ranger); as far as driving styles it was only me, same roads, same loads.

Enjoy!
 
Last edited:

msumms

New member
I've kept mine mainly stock. when i got it I was clocking 10-12mpg around town and 13-15 on the freeway. I started slowly replacing stuff preventatively and finally got around to the o2 sensors. pre cat sensor replacement with OEM got me to 15 around town and as much as 20 on the freeway (stock). Original fuel injectors. Do not run anything special; clean the throttle body, use champion copper plugs, OEM o2 sensor, my 96 gets decent mileage for its age. All my temp sensors were replaced before the o2 sensors and didn't help at all.

I saw a thread on naxja or cherokee forum once of someone who built and air dam and was clocking like 25-30 mpg. it looks awful though. But if you keep the skid plate off the front, i'd imagine you'll get worse mileage. having that skid plate under there will help move the air underneath similar to an air dam, though not the same.
 
Top