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Old 01-20-2007, 09:38 PM   #1 (permalink)
 
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Question Low gas mileage and low performance, whats wrong?

i have a 1993 Jeep grand cherokee 4.0 with 175k and it get's horribly gas mileage around 10.8 mpg, or atleast that's what the display average says on the ceiling of the car. It also has extremely low power some times. Some times it'll feel like it has very low power, sometimes it'll feel about average, and other times it feels plenty powerful...one suggestion a mechanic made to me was the type of gas but yet it does this on the same tank of gas, so thats not it.

It has a new o2 sensor, Cat, map sensor, plugs, and i am eventually going to get around to the dizzy cap,rotors, wires, and the fuel filter. Anything else i should look at or replace? or any suggestions on why my jeep is getting terrible gas mileage and bad performance? THanks for the posts.
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Old 01-20-2007, 11:00 PM   #2 (permalink)
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I would say the getting around to it eventually part, should be sooner than later.
I would start with the fuel filter, then do plugs and wires.
Also, figure your real mileage (miles driven/gallons used)
The displays are not usually very accurate.
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Old 01-21-2007, 11:43 AM   #3 (permalink)
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check your compression, thats a lot of miles. maybe its just getting old. maybe see if your fuel pressure regulator is working right. possibly stuck in the open position, or maybe a fuel injector stuck open.
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Old 01-22-2007, 07:54 AM   #4 (permalink)
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Take it to an exhaust shop. Sounds to me your converter is stopped up.
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Old 01-22-2007, 08:01 AM   #5 (permalink)
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i dont have the low power/ avg power feeling but my tj is lacking in the mpg department
my calculations show about 11.688 mpg now
and before i remember them to be about 15 mpg (highway)
both of these are with my 4 inch lift and thirty fives
the only possible thing i can think of is that i have trimmed the body a lot
could this have that much of an impact
the jeep is not that aerodynamic as it is
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Old 01-22-2007, 08:15 AM   #6 (permalink)
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How about air filter??? I know that can kill your mileage with a really dirty filter.
I would check the exhaust as well. We had an old Park ave that can like crap till we punched out all the junk in the converter. Then it ran pretty well.

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Old 01-23-2007, 09:34 AM   #7 (permalink)
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it is not the filter i just put a new fram in
ill check the converter but it is a 98 with only 72k on it
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Old 01-23-2007, 02:54 PM   #8 (permalink)
 
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u have to remember its full time 4wd, so that doesnt help.. i get 15 city/highway 145k miles
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Old 01-23-2007, 08:47 PM   #9 (permalink)
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Quote:
Originally Posted by Chevy4Life View Post
u have to remember its full time 4wd, so that doesnt help.. i get 15 city/highway 145k miles
yeah i know
but i was comparing the current mileage to what i had before with no "major"
changes
could it be that i am just on the gas too much
i know it is possible but i dont really feel like i was driving much different than before
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Old 01-23-2007, 08:53 PM   #10 (permalink)
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Did you notice this recently, as in during this winter?? I know that the gas is different during winter months and yields worse mileage.
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Old 01-26-2007, 10:14 AM   #11 (permalink)
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well i havent been here or driving for about six months
i know that it wasnt great before i left but it seems worse now
i have driving at the lowest rpms i can pull and it is doing a little better
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Old 01-27-2007, 06:22 AM   #12 (permalink)
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Quote:
Originally Posted by blegenam View Post
Did you notice this recently, as in during this winter?? I know that the gas is different during winter months and yields worse mileage.
That and people let their cars sit and idle more than in summer, which means worse mileage.
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Old 01-27-2007, 06:41 AM   #13 (permalink)
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Quote:
Originally Posted by npalinchik View Post

It has a new o2 sensor, Cat, map sensor, plugs, and i am eventually going to get around to the dizzy cap,rotors, wires, and the fuel filter. Anything else i should look at or replace? or any suggestions on why my jeep is getting terrible gas mileage and bad performance? THanks for the posts.
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Originally Posted by yotaboyz View Post
Take it to an exhaust shop. Sounds to me your converter is stopped up.
ADD can be a bitch I hear

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Old 01-27-2007, 06:54 AM   #14 (permalink)
 
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get some plugs and wires on there first should cange them at the same time. and get the good ones. I went through 4 sets be for i found my problem in my truck.
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Old 01-27-2007, 12:00 PM   #15 (permalink)
 
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whats a good set of plugs and wires? i was gonna go with the summit racing set up which included a new cap, rotors, and 8mm wires, along with new champion plugs. does that sound good ?
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Old 01-27-2007, 05:31 PM   #16 (permalink)
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What size tires are you runing? If they are 31" you could have 2 problems.
1. Is it geared for 31s?
2. Are you calculating for the additional distance traveled with larger than 29" tires?
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Old 01-27-2007, 09:38 PM   #17 (permalink)
 
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right now im running stock 235/75-15's and am looking to eventually go to 31's or maybe evern 32's, it looks like i have a lot of room my wells and as if i could fit 32's without a problem. although when i do this i will not be regearing? any thoughts?
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Old 01-27-2007, 11:35 PM   #18 (permalink)
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A quick way to check your rings on an I6 is to look at the air filter. When the rings start to go you get blow-by. The blow-by pushes oil out of the top of the valve cover at the PVC (like) valve which then will dirty up the filter with oil where the tube from the PCV valve connects to the filter box. I owned an I6 that needed a bottle to catch all the oil it was so bad that still ran, but with a diminished MPG. At any rate, 175k is not bad miles to get out of any motor and it just might be time.

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