Need input on my Bad MPG, I did search!

[Jacob789456]

Hi fellow KJ'ers. I do not post very often but I read the boards everyday.
I have a 2003 Jeep Liberty Limited 2wd with 19,000 miles (yes nineteen, it sat for 7 years after being wrecked) and I am currently getting an average of 8mpg city and at best 14 mpg highway with the 3.7 engine and 45rfe trans. I have the daystar 2.5 kit installed with 245/75/16 E range MTR's on and I have 3.73 gears. As soon as I can afford it I will install 4.10's or maybe even 4.56's because I am 2wd. I would like to know if these current mpg numbers sound reasonable due to my lift and bigger tires just because I am wondering if something else could be wrong. I have no current DTC codes, O2's seem to respond quickly, I have new air and fuel filters (i changed the one outside the tank, difficult...), and I recently changed the oil. Also I usually only run Shell or Chevron 89 or 91 and I run Techron concentrate just before every oil change (about every 4-5k miles). This last tank I filled up completely at 19,104 miles and today my gas light came on at 19,310 miles (206 miles on 16.5 of the 18.5 gallons). This is with 45% highway driving with no traffic at 65-70 and average city driving with very very few "rabbit" starts. Any input would be great and if new gears will help this mpg issue I will swap them in ASAP! Thanks for any help!

 

[yellocoyote]

When is the last time you changed spark plugs? Have you ever treated with Seafoam?

 

[Jacob789456]

I have never changed the plugs but I did pull them to put some marvels mystery oil down each cylinder before I started the engine after it sat for 7 years. The plugs looked fine and at the time, they only had 17k on them. Even with the low miles do you think it would be beneficial to change them. It's pretty easy to do on these motors and I will only use the OEM plugs. Also I have never seafoamed the motor. Thanks for the fast reply, any more input is appreciated!

 

[chill]

I gotta say I got a surprise after changing oil with synthetic and pulling and replacing the plugs with basic copper core autolites. Also setting the tire pressure. My avg. went from an overall of 16-17 "county" driving (around 45-65 mph) mix of hills and flats lights etc. all week, to now about 17-19 mpg. I use standard 87 octane with an additive every now and then.

Seafoam? I dun know. I'll try anything though if it works. I think the increase came from changing the plugs out. They were a weird champion type. they too looked good, but as I didn't know when the last time they were changed, since I bought the KJ used, i went and changed them. It's a cheap experiment.

Let me know if you get a solution, i'm game...

 

[Okura_hubby]

I bet one (or both) of the O2 sensors are bad causing the computer to go into a default mode. I am sure (and I dono) that a scan tool would tell you. When I was exploring the EFI options for my Ford Falcon, I came accross a 96 Ford Explorer which had the E (something) 2 - computer in it, meaning it had pre and post CAT O2 sensors. Since a 1963 Falcon really dont have any smog stuff on it, I was looking the best way to eliminate / reduce all unnecessary smog stuff. After long discussions you could run it without the sensors and you would get errors and the computer would run in a default mode vs active mode. So we explored other options, using a ECU out of a early 80's Cobra Mustang (which can be obtained via junk yard or parts store) then have a tuner reprogram it for my needs (since the early 80's Mustang ECU's are the more desirable ECU's for Tunners). So with that knowledge, I am betting your O2 sensors are bad. But before you replace anything of significant price I would have it scanned and see what the error codes tell you. Short of that we are just guessing.

Basic Tune Up stuff I would do anyway, you know.. Air Filter, Oil Filter, Oil, Plugs.. Just so when you do get it figured out your G2G. But beyond that I would see what the Scan says.

 

[Jacob789456]

I will check into the 02's again and I will change the plugs in the next few days. Any other input? Thanks for the replies everyone!

 

[Marty]

Sounds like bad mileage but hard driving will do it to Libertys. Going easy I get 15 mpg city, 24 mpg hwy if I keep it to 65 MPH, but down to 20 mpg if cruising 70-75.

 

[diyman]

'Italian tune-up' :smokin:, always worked for me!

 

[ridenby]

These things like copper plugs. 14 does not sound bad to me. IF I was to change gear ratio in a TWO wheel drive,4,56 or 488 would be the only choice.

 

[Jacob789456]

These things like copper plugs. 14 does not sound bad to me. IF I was to change gear ratio in a TWO wheel drive,4,56 or 488 would be the only choice.

Thanks for the input! This is my daily driver, would 4.56's be too tall or extreme for everyday city and highway use, and would the mpg's actually increase by a noticeable amount? I do not usually exceed 70mph but occasionally on runs through the desert on I10, I have to go 75 because traffic is doing 80 haha.