very bad gas mileage
CF Veteran
Joined: Aug 2010
Posts: 8,357
Likes: 103
From: Canton, MI
Year: 1999
Model: Cherokee
Engine: 4.0
Hi I see that this topic hasnt been touched in years but I was wondering if folks ever got the mpg issue fixed and if so what was it? I recently got a jeep(1998xj 4.0) and I'm avg 200mpgs per tank 
last things I need to check are: o2sensor(pre-cat), map, and maybe replace CAT...
last things I need to check are: o2sensor(pre-cat), map, and maybe replace CAT...I further suggest you use NTK O2S's (original factory O2S's were NTK).
Pre-Cat O2S = part number 23151
Post-Cat O2S = part number 23099
NTK O2S's are exact fit.
Rockauto .com probably has the best prices on these, although you can get them at the auto parts stores.
Don't change your Cat unless you have to. Changing the Cat to see if it improves gas mileage could be an expensive mistake. Same with the MAP sensor.
CF Veteran
Joined: Aug 2010
Posts: 8,357
Likes: 103
From: Canton, MI
Year: 1999
Model: Cherokee
Engine: 4.0
Newbie
Joined: Jun 2013
Posts: 21
Likes: 0
Model: Cherokee
I get about 160-180 miles in my '01 before my low fuel light pops up, which seems to be about 15 galllon of 20 total used.
Years back soemone stole my catalytic and I had it replaced with a cheaper universal model. Could that cause any problems?
Years back soemone stole my catalytic and I had it replaced with a cheaper universal model. Could that cause any problems?
Newbie
Joined: Jan 2015
Posts: 2
Likes: 0
Model: Cherokee
Yeah, that "fuel filter in the tank thing" came with the, I believe the 97+ XJs. The fuel filters in these are said to last until the fuel pump takes a dump. So, you change out both when opening up the gas tank. Trust, me. You won't want to do this just for the fuel filter. It is a royal PITA.
I see that this is a VERY old thread but we are currently having the same problem with my husbands 92 Cherokee...
Am I reading correctly that the fuel filter on the 92 model is NOT in the tank with the pump? I drive a 98, so mine is.... I assumed it was on the 92 as well and didn't look.
My mom actually drives a 96 (runs in the family) and she gets **** mileage as well. Neither of them have codes coming up...
Newbie
Joined: Jan 2018
Posts: 3
Likes: 0
Model: Cherokee(SJ)
**** for mpg
I ahve 1992 jeep xj sport and it was 18 mpg but it was leaking a little bit so i sent it in for a for a brand new tank and fuel pump. But ever sence then I normally get 10 to 12 mpg and i already changed my thermostat. It runs pretty good not like it is somthing to worry about. I have to put the co2 sensor in yet but you do you guys recommend for me to do?
CF Veteran
Joined: Oct 2018
Posts: 1,096
Likes: 166
From: Hunt County Texas
Year: 1995
Model: Cherokee (XJ)
Engine: 4.0L
I see that this is a VERY old thread but we are currently having the same problem with my husbands 92 Cherokee...
Am I reading correctly that the fuel filter on the 92 model is NOT in the tank with the pump? I drive a 98, so mine is.... I assumed it was on the 92 as well and didn't look.
My mom actually drives a 96 (runs in the family) and she gets **** mileage as well. Neither of them have codes coming up...
Am I reading correctly that the fuel filter on the 92 model is NOT in the tank with the pump? I drive a 98, so mine is.... I assumed it was on the 92 as well and didn't look.
My mom actually drives a 96 (runs in the family) and she gets **** mileage as well. Neither of them have codes coming up...
CF Veteran
Joined: Oct 2013
Posts: 5,924
Likes: 203
From: Greenville, SC
Year: 1999
Model: Cherokee(XJ)
Engine: 4.0
Originally Posted by downs
the pump mounted fuel filter wasnt a thing until they went to the returnless fuel system in 97 (I think it was 97) yours should have the frame mounted filter. Driver's side over the rear axle. Wix 33486
CF Veteran
Joined: Oct 2018
Posts: 1,096
Likes: 166
From: Hunt County Texas
Year: 1995
Model: Cherokee (XJ)
Engine: 4.0L
Newbie
Joined: Jan 2022
Posts: 1
Likes: 0
Model: Cherokee (XJ)
Location
Did you swap a big block into it
Seems like it could be a sensor, like an O2 sensor going south or it already left. It can also be a coolant temp switch, if those are bad your computer will be in "limp home-open loop" mode so your fuel mileage would be horrible. Your MAP sends the signal to control the fuel delivery and ignition timing. Heres how you can check to see if its bad. You need a high impedance voltmeter and thats it.
Step 1: with key ON and engine off, the voltmeter reading should be approximately 5 volts even.
Step 2: IF not at 5 then its bad. haha...simple huh, but if not continue.
Step 3: Test MAP sensor terminal 1 and 2
Step 4: Start the Jeep and make sure the voltage is between 0.5-1.8 with engine idling.
Step 5: Then check at WOT or wide open throttle, and make sure the volts are reading between 3.9-4.8
Step 6: If the sensor doesn't on either of these then check the vacuum line for leaks or blockage. If it doesn't have one of these its most likely your sensor.
Seems like it could be a sensor, like an O2 sensor going south or it already left. It can also be a coolant temp switch, if those are bad your computer will be in "limp home-open loop" mode so your fuel mileage would be horrible. Your MAP sends the signal to control the fuel delivery and ignition timing. Heres how you can check to see if its bad. You need a high impedance voltmeter and thats it.Step 1: with key ON and engine off, the voltmeter reading should be approximately 5 volts even.
Step 2: IF not at 5 then its bad. haha...simple huh, but if not continue.
Step 3: Test MAP sensor terminal 1 and 2
Step 4: Start the Jeep and make sure the voltage is between 0.5-1.8 with engine idling.
Step 5: Then check at WOT or wide open throttle, and make sure the volts are reading between 3.9-4.8
Step 6: If the sensor doesn't on either of these then check the vacuum line for leaks or blockage. If it doesn't have one of these its most likely your sensor.
Where is this coolant temp switch located?
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