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General Forums => The Mess Hall => Topic started by: spoonman on January 31, 2011, 10:52:01 AM
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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. :brick:
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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. :brick:
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.
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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.
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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...
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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
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also, make sure your t-case is not in 4wd
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the 4wd light isn't on and it rides fine on dry pavement..
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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).
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it should do better than 16 all stock 4.88s and 33s and few other things and im gettin around 17 sometimes more
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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..
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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.
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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.
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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. :confused:
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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. :confused:
lol, you're running 33's tho. This guys on stockers
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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
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something else I though of!! is it clutch fan I have seen them seize and be stuck on!! causing hp & fuel consumption.
2 is there anything else that could cause engine demand. aka big stereo? "causing alternator load" anything seizing up on the belt pulley's a/c bearing gone? etc?
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lol, you're running 33's tho. This guys on stockers
15-16mpg on 35's and 4.56's... My low was 11 though.
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15-16mpg on 35's and 4.56's... My low was 11 though.
us or imperial gallons?
and what speed do you drive??
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us or imperial gallons?
and what speed do you drive??
US.
0-75MPH...
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US.
0-75MPH...
auto trans right?
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auto trans right?
Mañuel
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auto trans right?
are you surprised by 16 or 11?
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are you surprised by 16 or 11?
Don't know why I :lol: at that.
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Don't know why I :lol: at that.
:wall:
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Compression test and leak down... ??
My 94 the mileage went to hell all at once the rings had given up at about 155K miles...
Dave
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mine's a '97 5 speed. the air filter is a new stock one. i pulled the k&n out awhile ago. the a/c isn't hooked up.no stereo. it's a completely stock '97.i live in ohio , so there some hills on the way to work and i don't drive fast. it's a 15 mile drive that is from 35-55mph with little stopping.i drive my hyundai accent and can squeeze 40-44 mpg out of it in the summer without a problem. i guess i'll do a compression check. i'm just under a half of a tank and i'm at 82 miles.
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AC really shouldn't matter since the compressor free-wheels if it's not on. 8mpg is a big drop though. Although 15 miles isn't that far and you say there are some hills. That's probably not helping. I do a 14mile commute as well but it's flat and at 35mph. Drops my mileage down to 15-16 from 17-18 that I got when I was doing 40m commute with the majority on the highway.
I even resorted to stripping down the Jeep and saw little improvement. This is because it's still a big block. I probably could regain 3-5 by going with smaller tires and drop the lift a bit. The biggest gain would probably come if I drove 50-55mph. That's what the Jeep was really meant for. Having to do 70-75 puts a lot of strain on the engine since it has to move all that weight and bulk through the air. I'm sure I could get 18 again if I was able to slow down. Maybe even break back into the 20's.
I don't think you told us what size tires you're running, lift and or if you recalibrate your speedometer.
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Mañuel
why not go 4.88's then? esp with 35's
other then that I got a fresh eng and I do get about 15mpg like you do jeffy but I do mostly town driving with the occasional highway mainly to go wheeling.
last time I actually did the math on the highway I got about 20-21mpg with all highway no town and it's because I did a long distance trip.. I was pulling a tiny trailer with a MiniZ on it "could not feel it" when on the highway cruising. but I must say I was doing mainly 50-55mph or less for speed. I was completely stock with 31x10.5r15's on stock gears.
as soon as I got to my destination I refueled and did the math for light to light with the little trailer stop and got dropped it to about 10mpg or less in town with the trailer on the back "can really feel the power loss and weight" in town.
so if you are bone stock you should be getting better then 8mpg.
engine wear like already said "compression check" etc should be checked first if you have not done that.
after that I would go after a clutch fan or something sticking on when driving highway thats not suppose to.
then I would go after such things like 02 sensors. I have even seen new ones be bad!!! scan tool could help this diag. possibly!!
no drive line bearing gone? high resistance in a diff or wheel bearing?
there is lots of stuff that can cause fuel consumption..
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why not go 4.88's then? esp with 35's
...There was once a time when there were no 4.88's...
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...There was once a time when there were no 4.88's...
:lol: I remember those days.
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...There was once a time when there were no 4.88's...
still doesn't answer why you don't know lol
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they exact setup i have now was getting 23mpg @65 mph on freeway and 18 in town. jeep was on the scanner today. there is no timing adjustment, but we could see it didn't advance consistently. sometimes was perfect other times it would hesitate and advance with inconsistent numbers. fuel press looked good.
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The difference in mileage for me is about 4 MPG driving 75 instead of 55 on flat ground.
Just a small data point.
Warmed up YJ engine with headwork, cam, light pistons balanced etc...
Dave
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still doesn't answer why you don't know lol
You asked;
why not go 4.88's then? esp with 35's
Like I said, there were no 4.88's available at that time. And to do it over again is a waste of money. It's not that big of a difference. I'm holding off for 5.13's (with 33's) or 5:38's (with 35's) which will get me back to stock.
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they exact setup i have now was getting 23mpg @65 mph on freeway and 18 in town. jeep was on the scanner today. there is no timing adjustment, but we could see it didn't advance consistently. sometimes was perfect other times it would hesitate and advance with inconsistent numbers. fuel press looked good.
most obvious reason for out of whack and erratic ignition timing would be the crank sensor.
EDIT: how did the MAP and TPS output look?
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You asked;
Like I said, there were no 4.88's available at that time. And to do it over again is a waste of money. It's not that big of a difference. I'm holding off for 5.13's (with 33's) or 5:38's (with 35's) which will get me back to stock.
:thumb:
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map and tps were fine. i called a bud who plays with jeeps. he said crank sensor too. he also said ignition module if crank sensor wasn't problem. i just hope it's something easy i can do. thanks for all the help.
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map and tps were fine. i called a bud who plays with jeeps. he said crank sensor too. he also said ignition module if crank sensor wasn't problem. i just hope it's something easy i can do. thanks for all the help.
hope you figure it out soon, chasing gremlins isn't always that easy!!
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map and tps were fine. i called a bud who plays with jeeps. he said crank sensor too. he also said ignition module if crank sensor wasn't problem. i just hope it's something easy i can do. thanks for all the help.
unfortunately there is no ignition module, is integrated in the PCM (ecu) so that would be a bummer.
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unfortunately there is no ignition module, is integrated in the PCM (ecu) so that would be a bummer.
What do PCM's sell for? Can you buy a used one or is it better to buy new?
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What do PCM's sell for? Can you buy a used one or is it better to buy new?
buy used, new are too much $$$ (and with YJs in our case would be hard to find anyway, but you never know some nos sale could turn out cheap).