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11 mpg - is this right?

S

Sandydog

NAXJA Forum User
Location
Albany, NY
I'm getting 11 mpg on my 2000 4.0, what can I do or check to increase this? Most of driving is around town but this jeep has me at the pump more then I would like. I see others are getting up to 19 mpg. I did have the plugs changed recently.
 
Have you changed your tire size from the stock size?
What is the gear ratio you are running? Have you changed the gears and not changed the speedometer gear to match the gear ratio and tire size?
When was the last time you did a tuneup?
Do you have any CELs (Check Engine Light)?
Are you the original owner and how old are the primary O2 sensors?
Do you have any exhaust leaks in you header or exhaust system?

These questions should help you diagnose your gas mileage problem.
 
Everytime I see one of these threads it makes me wonder what's wrong with my Jeep. Complete tune up at 90K miles and I was still getting 11.5mpg. Just replaced my O2 sensors and that bumped me up to 12.5mpg, which I was OK with, until I read this thread... I feel your pain. I think the only thing I haven't ruled out is exhaust leaks. I know I have a leak just after my cat as condensation leaks from there as it warms up. Could that really affect my fuel mileage that much though?
 
fyrfytr1717 said:
Everytime I see one of these threads it makes me wonder what's wrong with my Jeep. Complete tune up at 90K miles and I was still getting 11.5mpg. Just replaced my O2 sensors and that bumped me up to 12.5mpg, which I was OK with, until I read this thread... I feel your pain. I think the only thing I haven't ruled out is exhaust leaks. I know I have a leak just after my cat as condensation leaks from there as it warms up. Could that really affect my fuel mileage that much though?
Click to expand...

Same with me. I have a '91 with 75K on it, full tune up recently, Replaced the entire exhaust system last month (except header, which is not original and was done by the dealer) including o2 sensor, entire cooling system, checked TPS according to FSM, cleaned throttle body and sensors, and I'm only getting 12mpg. Bone stock.
 
Last edited:
how hard do you guys drive? I run 33"s 4.56s, an aw4 and I get 14 around town and up to 18 or 19 highway.
 
Has anyone changed their Coolant Temp Sensor? Not sure where it is OBD1, or if RENIX even has one, but '96+ OBDll it's the sensor in the t-stat neck. There's a table of resistance values somewhere here in the hallowed halls of NAXJA, and it did the trick for me. A fresh O2 sensor and CTS-along with new injectors-got my '96 over 20 MPG. On regular 87 gas again!

Of course, ethanol and 'winter blend' gas doesn't help.
 
CTS table
Resistancetable.png


I don't know what you read, but no one is getting 19mpg in city driving. Most XJ owners are probably lucky to get 19 on the highway.
 
my xj is averaging about 320 miles per tank. 97 auto 3:55 gears bone stock on 225/75/15s.

my last xj had a 4.5 lift, 34" swamper LTBs, auto 4:10s, armor, and i was getting 185 per tank.
 
My mPG has taken a drop off recently, I am at 2" lift with 30s stock gearing I drive 99% city no freeway at all. I used to average 250 miles before my fuel light came on and put in 15 gallons of gas between fill ups. Now I am down to 200 miles before my light comes on which is ruff. I didn't think 30s would need re-gearing, my MPG was steady for a while after the lift and bigger tires and has been dropping off(before the winter gas mix came around).

I have a new coolant temp sensor, main o2 sensor, CPS, fresh oil change, fresh air filter, cleaned IAC, recent plugs and wires, rotor and cap, distributer is newish and a bunch of other stuff.
 
rockclimber said:
how hard do you guys drive? I run 33"s 4.56s, an aw4 and I get 14 around town and up to 18 or 19 highway.
Click to expand...

With the combo in my signature (looks to be the same as yours), I'm lucky if I eek out 13+mpg with the cruise control set at 65mph on flat ground. 18 to 19? Not a chance for me. Admittedly, I should probably try it without my roof rack sometime just to see exactly how much fuel mileage that is costing me.

Maybe I need to consider some new engine sensors along with my exhaust leak? Seeing a lot of people mentioning new sensors...
 
Not to do the "new guy" thing but are you calculating your new mpg's compensating for how much your speedometer/odometer is off by when changing tire sizes?

What should a 4 door 5 speed stock Cherokee be getting (4.0L)?
 
This is the same issue I am having. I have no exhaust leaks-all new,all new sensors that test good. If new 4.10 gears for my 31's dont fix the mileage I will go back to driving my 78 chevy 4x4 with a 454 and 4 speed with 36" swampers and 6" lift as it gets roughly 15 on the freeway with 3.73 gears. And is way more capable offroad than my jeep and can actually pull a trailer up a hill at speed without overheating. Its sad to think that the jeep 6 is that much of a gas hog over a 454.
 
comics22 said:
Not to do the "new guy" thing but are you calculating your new mpg's compensating for how much your speedometer/odometer is off by when changing tire sizes?
Click to expand...

Of course, new speedo gear back when I changed tire size and again when I regeared years later. Within 1mph at 70mph according to GPS.
 
According to the police setup speed radar sign in my neighborhood the other day, my speedo is right on the money or their gear is off ha.
 
lol we have some of those on the highway, its always off. unless my spedo AND gps are off (both are dead on)...my record is 85 in a 50 in a car that shouldn't be trusted above 60
 
It was accurate for 3 of my vehicles, unless all 3 are off which would be weird, 2 of my cars are stock wheels/tires all the way. No way to know unless I had some kind of calibrated GPS I guess.
 
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