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REALLY BAD FUEL ECONOMY

jchawks

NAXJA Forum User
Location
North Carolina
I have a 2001 XJ. I am getting 12 MPG (highway). I really need to improve my fuel economy as this vehicle is a daily driver. Admittedly, I am running alot of modifications/weight. They are listed below:

Tires:
31" BFG AT/KOs

Engine: Edge Trail Jammer Performance Kit (w/ cold air intake and throttle body spacer)

Body:
ARB Deluxe Winch Bull Bar w/ WARN winch
ARB 43" X 49" Roof rack w/ mesh floor
WARN Rock sliders
WARN Rear bumper w/ spare tire carrier

Obviously, I do not want to remove weight but am willing to take off the rock sliders as I rarely need them. No amount of advice will insult me as I'm not a very mechanically gifted guy. I have NOT replaced the plugs and wires lately. I looked for ignition kits but noticed they are mostly for the earlier XJs. Is there a device I can purchase to help me out? Any other ideas?

Thanks,
JC
 
I would start with a new set of spark plugs and disconnect the battery while you change them out. This will help the computer to reset itself. Also, the roof rack is probably costing a couple MPG all by itself from wind resistance.
 
Put an egg between your foot and gas pedal.

Auto or manual transmission?

I'm assuming you haven't regeared which only exacerbates the problem.
 
I feel your pain. I also get 13 MPG and that is with 4.10s!! Granted I do not have the lightest foot but........

These things are as aerodynamic as a brick and about as high tech.

Setup is in the signature.
 
I would suggest 4.10 or 4.56 gears.. you have a lot of extra weight to push around.

Got a long highway trip coming up? Drive in 3rd gear for a while (put it in '3' so the torque converter locks up correctly). Run for 75 miles and refill the tank, see what kind of mileage you got.
 
I'm willing to bet that roof rack is where a good amount of the mpg's are disappearing too. Those things kill aerodynamics more than any of those other mods you've listed.
 
Dude you gotta ditch the roof rack, thats a HUGE culprit right there. More often than not I see guys driving around with a huge roof rack, with nothing in it.
 
XJ Peeps,

Thanks for the feedback...

Durango Bob: Thanks. Will do. Any particular brand of plugs/wires?

Karstic: My XJ is an automatic. Was thinking about a re-gear... Why should I NOT do that?

Cal: Am considering some new gears... Just came back from a long trip but will try driving in "3" a little on the next one.

Durango Bob, Begster and AZ XJ: I hear you on the roof rack but everytime I take the Jeep on a long trip I depend on it. The rack can't go. I'm gonna have to shave some MPGs from somewhere else.

Here's my full set-up...
2001 Jeep Cherokee Sport, 60th Anniversary Edition - Engine, Transmission and Drivetrain: 4.0L, Automatic, Edge Trail Jammer Performance Kit, Stock Transmission, Stock Gears, Slip Yoke Eliminator (Unknown Brand). Suspension, Tires and Rims: 4.5" BDS Suspension Lift, BFG A/T KO 265/75R 16, Stock 5 spoke mag rims. Other Modifications: ARB front bull bumper, WARN winch, Two KC Slim-lights on front bumper wired to factory fog light switch, WARN rock sliders, WARN rear bumper w/ tire carrier, full spare on stock rim, ARB Full rook rack mounted to rain gutter.
 
Well, you don't have to worry about wires on your 2001. How many miles are on it? Have the o2 sensors been replaced? I have an 2001 with 245/75R16 and my mileage dropped from 21 mpg highway to 18 mpg highway when I added the tires. I also did the ZJ fan clutch upgrade at the same time which doesn't help. A re-gear to atleast 4.10's, maybe 4.56's with all that extra weight would help.
 
XJ Peeps,

Thanks for the feedback...

Durango Bob: Thanks. Will do. Any particular brand of plugs/wires?

Karstic: My XJ is an automatic. Was thinking about a re-gear... Why should I NOT do that?

Cal: Am considering some new gears... Just came back from a long trip but will try driving in "3" a little on the next one.

Durango Bob, Begster and AZ XJ: I hear you on the roof rack but everytime I take the Jeep on a long trip I depend on it. The rack can't go. I'm gonna have to shave some MPGs from somewhere else.

Here's my full set-up...
2001 Jeep Cherokee Sport, 60th Anniversary Edition - Engine, Transmission and Drivetrain: 4.0L, Automatic, Edge Trail Jammer Performance Kit, Stock Transmission, Stock Gears, Slip Yoke Eliminator (Unknown Brand). Suspension, Tires and Rims: 4.5" BDS Suspension Lift, BFG A/T KO 265/75R 16, Stock 5 spoke mag rims. Other Modifications: ARB front bull bumper, WARN winch, Two KC Slim-lights on front bumper wired to factory fog light switch, WARN rock sliders, WARN rear bumper w/ tire carrier, full spare on stock rim, ARB Full rook rack mounted to rain gutter.



So you have 32's, not 31's..


So stock: (3.55/225 tires)

65 mph -
3rd gear - 2741 RPM
4th gear - 2056 RPM

You now: (3.55/265 tires)

65 mph
3rd gear - 2450 RPM
4th gear - 1837 RPM


You with 4.10 gears / 265 tires

65 mph
3rd gear - 2829 RPM
4th gear - 2122 RPM

You with 4.56 gears / 265 tires

65 mph
3rd gear - 3147 RPM
4th gear - 2360 RPM


4.10 gears would put you at pretty close RPM's to stock, but would not help to compensate for the load you are carrying, nor the loss of aerodynamics from your lift, roof rack, etc.

4.56 gears would run you at higher RPM's, but help with the extra oomph you need from your build. You may lose just a little economy on flat ground, or downhill with a tailwind, but you would gain around town, starting, uphill, etc. In the end it would probably be a net gain, not to mention the increased driveability.

Running around in 3rd gear now would put you at pretty close RPM's to where 4.56 would give you. 2400 may sound high, but believe me, it is not. I run around at ~2700-3200 with my stroker on 37's all day, and the engine loves it. The 4.0 (or stroked version) would rather spin at 3300 RPM's all day than work hard.

The third gear test won't help you around town, so its really not a true comparison, but if you were going on a longer highway trip, and filled up right before / right after the highway, may give you a reasonable idea what 4.56's would be like for power and economy.

It is really hard to gear a cherokee too deep. One of our locals ran around for a while with 215/75/15 tires, 4.56 gears and detroit lockers. It spun a little fast on the highway, but he still did 70 mph at 16 mpg or better, and it was a ton of fun.
 
Run a can of BG44K through the gas to clean the carbon and injectors. Don't waste your money on the other cleaners other than Lucas. BG44K is the best, followed by Lucas but BG is worth the extra bucks.
 
My thoughts are:

As mentioned roof rack and spark plugs etc.
the fuel injector cleaner-not a bad plan at all, might consider fuel filter too if not in gas tank I don't know where they are
gears-good will help pull the extra load
clean air filter
do you have a front skid? they're not much in protection really but I think they're great at reducing drag for highway driving.
when i replaced my o2 sensor it improved my gas mileage tremendously, I think I read they're good for 60k or so, someone correct me if I'm wrong. but if thats old and corroded it may be contributing.

EGG between foot and pedal by far #1 important thing for gas mileage:wave1:
 
Do you need the roof rack to cruise around town? Take it off and only put it up there wen you are going on a long trip.
 
You need to regear & lose the rack.

I run the same tire size (265x75x16) on the same truck (2001 auto, HD Bumpers, Rails, etc..), I am geared to 4.56 with no rack, I average around 17MPG on the highway (14MPG overall) & I have a very heavy foot!

If you stay on road & don't climb many hills (Or tow anything) I would go with 4.11s, My MPGs were around 19-20 Hwy when I ran 4.11s.

PS: and my speedo is properly calibrated!
 
Yeah, something is up here. I run a 2001 60th Anniversary auto with 31's and 4.10's. I had 3.55's earlier, and even with those I got 19 highway. You need to check your plugs and make sure that everything is working properly with your engine and fuel system. Maybe that Edge is improperly calibrated? I dunno...I have a roofrack too soo *shrugs*
 
I gained a little from some Precision auto Injectors. (1 or 2 mpg)

I also run 265/75's, and I have 4.56's. Mpg on flat ground can be up to 19 mpg, with hills an average of about 17.

I would ditch that arb bumper. Light is better. My rigidco bumper is only 50 something pounds.
 
Specs:

00' With stock bumpers / body and a Con Ferr roofrack with my spare up there and 4 Hella 500FFs.
4.5" Lift with 32s
Stock Gearing
AW4 / 242

Offroad in 4WD Low -- 7-10mpg
Around town in Full-Time 4WD (Weather) -- 10-12mpg
Around town in 2WD -- 12-16mpg

I have some sea-foam that I'm going to run through the engine soon and do an oil change with new spark plugs and hopefully I'll see some of these numbers go up. The roofrack surprisingly doesn't feel like it adds any drag, you're already driving a toaster. :rof:
 
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