Gas Milage

[Darko154]

I have an 02 renegade with 245 70 16 and drive without pushing my petal to the metal. i just got my throttle body cleaned, got new plugs e3's and radiator is really clean. the only part that doesint work and i have one coming in is my radiator cooling fan. i am getting 11 miles to a gallon right now. i am running out of ideas on what else to do. some people tell me that the 100k mark i just hit affects the engine to a point where i get horrible gas milage and some say it might be a bad fuel filter... if you have any type of other ideas or agree with what others say please tell me. and also if you have a liberty which is like mine please tell me what mpg your running.

 

[Ry' N Jen]

I just run stock spark plugs for starters...
All those fancy expensive ones are just a waste of cash.
Our KJ has 226000 kilometers/140429.9 miles on the clock
and although not the greatest fuel economy we still manage
about 23 MPG on the freeway!
In the city it's about 13-15 MPG right now.

 

[LibertyFever]

Just how are you calculating your gas mileage? Have you had your BCM set for the larger tires? That can through off your speedometer, your odometer and of course your gas mileage calculations.

The last time I calculated mine I was running about 19 MPG Highway. I'm running ProComp LT245/75R16 AT's and my BCM is programed for them.

 

[Darko154]

so any idea what might b cause my awful mileage???

hmm...i dont know what you mean by BCM, but i calculate per tank and i almost only drive city. the last tank i got just under 200 for 17 gallons

 

[LibertyFever]

so any idea what might b cause my awful mileage???

hmm...i dont know what you mean by BCM, but i calculate per tank and i almost only drive city. the last tank i got just under 200 for 17 gallons

The BCM is the engine computer. It goes by a few names.
Is your speedo accurate?

 

[tjkj2002]

so any idea what might b cause my awful mileage???

The spark plugs you installed are the biggest factor in poor mpg's.Put copper core plugs back in.


2nd is your PCM still thinks you have stock tires on and makes the trans shift poorly also resulting in bad mpg's.The final factor is now your ODO is wrong due to bigger then stock tires throwing your mpg's off as your actually going father then what your ODO is saying you are.

 

[Darko154]

city yes when im on the highway its off like 2-3 miles

 

[tjkj2002]

The BCM is the engine computer. It goes by a few names.
Is your speedo accurate?

The BCM is the Body Control Module,the PCM controls the engine,the TCM controls the trans.

 

[Darko154]

alright how would i change it so my computer takes the bigger tires?

 

[tjkj2002]

alright how would i change it so my computer takes the bigger tires?

Only the delaership can do it via the DRBIII,it's called a "Pinion Reset",will charge anywhere from $50-$150.

But your biggest mpg killer is those E3 plugs,nothing but problems with those plugs.

 

[Darko154]

ok so i need to go to a dealer and get the BCM reset to the right sized tires, and then get my plugs changed? what kind should i get for performance? and gas milage?

 

[Ry' N Jen]

ok so i need to go to a dealer and get the BCM reset to the right sized tires, and then get my plugs changed? what kind should i get for performance? and gas milage?

Like Troy and I said, just use stock copper core spark plugs.
Then go get the "Pinion Reset" done.

When I had the "Pinion Reset", the service manager, nor any of the mechanics had never heard of it!
Fortunately for me, our KJ was the guinea pig and it was done free of charge.

You never know, you might just get lucky!

 

[tibby]

i have a 05 libby with 245 70 16s as well. I am getting about 25 mpg strictly highway. I thought the computer for the OD automaticlly adjusted for the larger tires? The speedo is correct (or at least its the same as a toyota tundra). Running cheap copper plugs, regular oil changes,correct tire pressure, CLEAN air filter...those little things won't help that much...look behind the jeep, maybe you have a piano tied to it?

 

[LibertyFever]

i have a 05 libby with 245 70 16s as well. I am getting about 25 mpg strictly highway. I thought the computer for the OD automatically adjusted for the larger tires? The speedo is correct (or at least its the same as a toyota tundra). Running cheap copper plugs, regular oil changes,correct tire pressure, CLEAN air filter...those little things won't help that much...look behind the jeep, maybe you have a piano tied to it?

If I'm not mistaken the Liberty's BCM also influences the automatic transmission's shift points. So if you have non-stock wheels and you haven't updated your engine computer (BCM) then not only will the speedo be off but the transmission will shift at the wrong point.

Also I've read that on Liberty model years before 2008 you could program the tire size. After 2008 you had to program the size or revolutions.

The ultimate best way to calculate your gas mileage would be to use a GPS device not your odometer.

 

[Luke]

I wish you luck with the pinion reset.. I am told by two different dealers that it cannot be done on my 05. Hasn't really effected my fuel economy much though. Just make sure, as others have said, that you are using the right #'s ... your driving farther than your odo is telling you.

 

[J-Thompson]

The PCM reset for larger tires is "a load of horse crap" as per the only guy I will trust to do more than an oil change on my rides
yeah it will correct the speed but that is it and how far off is it?
mine was only 2-3 MPH off at 65ish
not at all worth it
use a GPS to see how far off it is
then you will know if you are spending money for nothing
we did not change a thing on ours and it ran fine for over 40K miles on 245/75's
and we averaged 17 mixed driving

I would bet on the plugs

 

[tjkj2002]

The PCM reset for larger tires is "a load of horse crap" as per the only guy I will trust to do more than an oil change on my rides
yeah it will correct the speed but that is it and how far off is it?
mine was only 2-3 MPH off at 65ish
not at all worth it
use a GPS to see how far off it is
then you will know if you are spending money for nothing
we did not change a thing on ours and it ran fine for over 40K miles on 245/75's
and we averaged 17 mixed driving

I would bet on the plugs

Not a load of crap,even if your speedo was off before your TCM was operating at that set of revolutions per mile,change that # and it confuses the TCM.My trans would hunt all the time before the pinion reset was done after adding 265/75's and 4.10's,afterwards it shifted like it did when stock.

 

[J-Thompson]

Not a load of crap,even if your speedo was off before your TCM was operating at that set of revolutions per mile,change that # and it confuses the TCM.My trans would hunt all the time before the pinion reset was done after adding 265/75's and 4.10's,afterwards it shifted like it did when stock.

I guess so
the tires you added were 3"+ over stock mine were less 2
you changed gears I did not

I am running tires that are almost 5" over stock on the TJ
never had an issue
and no gear hunting
kind of hard to hunt for gears when it only has 3 to pick from

 

[Darko154]

Wow so much debate here haha. ill check a dealer if its free ill do it otherwise it doesint feel like any different from when i got my jeep. thx all

 

[Doublecardan]

I think one of the main reasons that your mileage is so poor is that you said you use it mostly in the city. I dont think the od gets used much in that case and even if it did the od has nearly 1000 rpm drop, each time you pressed the pedal it would go back up again.