Bad MPG in 99 xj
Thread Starter
Senior Member
Joined: Apr 2009
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From: Durant,Oklahoma
Year: 1999
Model: Cherokee
Engine: 4.0 HO
But I did want to point out that there are a few things left you could check without convincing yourself you are bats for tackling an imaginary problem
I've never heard of it jumping, I've heard of people stretching their timing chain to the point it sounds like they have lifter tap really bad or even a mild rod knock. If your timing chain is bad then you'd know because it'd be making a horrid racket and the Jeep wouldn't be running right
Last edited by 4.0cherokee; Mar 2, 2010 at 07:34 AM.
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The timing chain can stretch on high-mileage engines and can produce symptoms such as lack of power, poor gas mileage, engine misfire, backfires, etc. Really all depends on how off it is - if at all.
Searching the net it doesn't seem like it happens often with this engine with some folks saying their chain has stretched with around 130K on the engine and others over 200K with no ill symptoms.
I'm just not familiar enough with this engine to tell you exactly what to do to test it other than pull off the timing cover and measure the slack. Search the net.
But I did want to point out that there are a few things left you could check without convincing yourself you are bats for tackling an imaginary problem
Searching the net it doesn't seem like it happens often with this engine with some folks saying their chain has stretched with around 130K on the engine and others over 200K with no ill symptoms.
I'm just not familiar enough with this engine to tell you exactly what to do to test it other than pull off the timing cover and measure the slack. Search the net.
But I did want to point out that there are a few things left you could check without convincing yourself you are bats for tackling an imaginary problem
Honestly, if someone goes through all the hassle of pulling the timing cover off(a huge pain in the rear) they might as well drop the $60 and put a new timing chain on. Especially if their engine is over 100,000 miles.
Are you going to leave me hanging on what they are? I am ordering a cfm tri core radiator this week. Do you want to help me add anything to the list that is going to help it run better?
Well it sounds fine. Other than when i was putting gas in it the other day and all of a sudden started to act like it was going to die, then it reved its self up.
Well it sounds fine. Other than when i was putting gas in it the other day and all of a sudden started to act like it was going to die, then it reved its self up.
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Joined: Jan 2010
Posts: 189
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From: St Augustine, Fl
Year: 1999
Model: Cherokee
Engine: 4.0 Power Tech
MPG
I drove my 99 Sport to Orlando yesterday at 65 mph, it was 234 miles and it took 1/2 tank. I have a stock Sport with 140k and 235/70r/15's Firestone Destination's.
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Joined: Jan 2010
Posts: 189
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From: St Augustine, Fl
Year: 1999
Model: Cherokee
Engine: 4.0 Power Tech
MPH
Years ago I owned a 70 Box Bronco with the small 6 cyl and 411 gears. I installed fender flares and 8x15 wheels with 30 inch tires. Before the mod my little Bronco would get about 20 mpg at 55mph after the big tires it dropped to about 13 mpg even at 60 cents a gallon the big tires didnt stay long and I went back to radial street tires. I never had a problem in the woods and hills of Kentucky.
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Joined: Aug 2008
Posts: 231
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Year: 1992
Model: Cherokee
Engine: 6
Heres a bit of news that may help some.
I recently installed an AFR gauge to objectively observe the changes as I tweek with the MAP & O2 sensors. Its a narrow band system, so the price was right. Well, as my daily travels are in the mountains my readings are pretty much all over scale but a pattern emerged and I have been able to see results with EFIE adjustments.
Today I thought about the post from Chrkee313 who replaced his IAT sensor. So I figured that it might be worth a try. It worked! I could instantly see the AFR lean out almost a full point to where I had to back off my EFIE setting. I noticed the AFR needle was not hunting under constant throttle. There was also a change in power as indicated by my butt-o-meter.
For now the results are still very inconclusive, but definitely a change for the better.
BTW the probe was not easy to find under the common name of IAT. Kragens/O'Rilley listed it as an Air Charge Temp sensor. (PN WT3023)
I recently installed an AFR gauge to objectively observe the changes as I tweek with the MAP & O2 sensors. Its a narrow band system, so the price was right. Well, as my daily travels are in the mountains my readings are pretty much all over scale but a pattern emerged and I have been able to see results with EFIE adjustments.
Today I thought about the post from Chrkee313 who replaced his IAT sensor. So I figured that it might be worth a try. It worked! I could instantly see the AFR lean out almost a full point to where I had to back off my EFIE setting. I noticed the AFR needle was not hunting under constant throttle. There was also a change in power as indicated by my butt-o-meter.
For now the results are still very inconclusive, but definitely a change for the better.
BTW the probe was not easy to find under the common name of IAT. Kragens/O'Rilley listed it as an Air Charge Temp sensor. (PN WT3023)
Thread Starter
Senior Member
Joined: Apr 2009
Posts: 925
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From: Durant,Oklahoma
Year: 1999
Model: Cherokee
Engine: 4.0 HO
do you think that changing the coolant sensor will help either? I have had to run some radiator leak stuff through it and I didnt know if maybe that could have plugged it the sensor some. It shows to get warm quickly and stays at 210 all the time but i didnt know if it might be a good idea to replace it as well
Member
Joined: Aug 2008
Posts: 231
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Year: 1992
Model: Cherokee
Engine: 6
My XJ is stock with 110K on the clock. 15 MPG's
Oh. Added a TB spacer a year ago. That was a waste of money.
http://www.fuelsaver-mpg.com/doc/TuningForMileage.html
Oh. Added a TB spacer a year ago. That was a waste of money.
http://www.fuelsaver-mpg.com/doc/TuningForMileage.html
Last edited by JrRifleCoach; Mar 3, 2010 at 10:21 AM.