Topic: ugh i give up...

[spoonman]

just had the jeep put on the scanner. nothing wrong with it and it's not throwing codes, but i just get 8.5 mpg on last tank. it seems to run fine, but obviously it isn't. it has had new plugs, new cat, new muffler, new coolant temp sensor. i'm out of guesses and everything is stock on it. i can't imagine the winter mix of gas would do this much to my mileage. any ideas? i'm ready to roll it down the hill.

[sharpxmen]

just had the jeep put on the scanner. nothing wrong with it and it's not throwing codes, but i just get 8.5 mpg on last tank. it seems to run fine, but obviously it isn't. it has had new plugs, new cat, new muffler, new coolant temp sensor. i'm out of guesses and everything is stock on it. i can't imagine the winter mix of gas would do this much to my mileage. any ideas? i'm ready to roll it down the hill.

1. You have larger tires and don't account for the error on the odometer (although should still not be getting 8.5mpg even with that error).
2. you have a hole in the tank or some of the lines are sipping out fuel when the engine is running (like having a micropore and that would spray mist out - but you should be able to smell the gas in that case, i say micropore as otherwise it would run like hell and you'd be able to see the gas pouring out).
3. you might have an issue with too much fuel pressure, i had my return line plugged and I was getting some bad mpg, easy to test on a YJ (not sure what you have) - unplug the return from the injector rail and blow in it.

you might want to test the fuel pressure and also maybe put a scanner on it and check the fuel trims.

[aw12345]

With a scanner look at engine temperature, fuel trim and map sensor voltage and go
from there. a check of ignition timing would not hurt either.

[Trainman638]

Just a thought...try a locking gas cap for a week and see if mileage improves. I had a truck once that only got 9mpg and should have gotten 16+. I watch my mileage more for maintenance than economy (them squirrels get hungry) so, when the mpg drops 50% I start searching for a cause. I found it one night crossing my yard with a gas can and hose! Teenagers...

[spoonman]

tires are stock 15". no gas leaks for sure. i forgot to ask my mechanic what the fuel pressure was. he didn't have time to check my timing, but said to check it.it's not teenagers, but i wish it was. i went for a 20 mile trip and watched the gas gauge move almost 1/4 of a tank. i'll call him now. thanks for tips

[sharpxmen]

also, make sure your t-case is not in 4wd

[spoonman]

the 4wd light isn't on and it rides fine on dry pavement..

[sharpxmen]

do a scanner and pressure check then. With stock tires (27 to 28'' diameter) you should be over 16mpg (and probably even better than that).

[knotts89]

it should do better than 16 all stock 4.88s and 33s and few other things and im gettin around 17 sometimes more

[Torch_Ind]

my first question is how fast do you drive?? if your trying to go over 60mph with your foot near the floor to keep high speeds it will drain your tank..  

number 2 : whats the terrain like in your area? lots of big hills?

number 3: also don't see a mention of air filter checked?

number 4: have you tried a O2 sensor? especially if it's a YJ..

[sharpxmen]

my first question is how fast do you drive?? if your trying to go over 60mph with your foot near the floor to keep high speeds it will drain your tank..  

should still be better than 8.5mpg, i was getting 13 driving like that with 33x12.5 and 4.10 gears.

[neale_rs]

With a scanner look at engine temperature, fuel trim and map sensor voltage and go
from there. a check of ignition timing would not hurt either.

x2, make sure your computer knows when the engine has reached full temperature.

[k]

man, you guys are making think there is something wrong with mine!   I only average 10 MPG!  Mine is auto and geared with 4.10's though, and I almost never have any type of top or doors on it.

[RT]

man, you guys are making think there is something wrong with mine!   I only average 10 MPG!  Mine is auto and geared with 4.10's though, and I almost never have any type of top or doors on it.

lol, you're running 33's tho. This guys on stockers

[Torch_Ind]

tires are stock 15". no gas leaks for sure. i forgot to ask my mechanic what the fuel pressure was. he didn't have time to check my timing, but said to check it.it's not teenagers, but i wish it was. i went for a 20 mile trip and watched the gas gauge move almost 1/4 of a tank. i'll call him now. thanks for tips

I still want to know what speeds and terrain this was in? 

for ideal you need long flat highway and do 55-60 mph max

even if you had a spot were there was a gas station.  fill your tank and record how many clicks you do I would make it kick off, I would do it twice "kick off off the fuel pump" do a run one way for as long as you can stop turn around and come back and repeat filling your tanks and wright down your info aka gallon's & miles driven. at your turn around spot try to get up to speed without stomping on it.  I would also recommend doing 55mph highway and do the speed limit. and then do the math to find out what you got for miles and see if your still only getting 8mph