1990 XJ 11.5 MPG help needed
CF Veteran
Joined: Jan 2013
Posts: 1,029
Likes: 35
From: Colorado
Year: 1991 2-Door
Model: Cherokee
Engine: 4.0 liter
Maybe I missed it in all of these posted I did not see anywhere the op said how he calculated his mileage without changing the speed-o-gearing to be an accurate 11.5 mpg. I don't know what the mathematical equation would be to figure the true mileage after putting on taller tires? I waited until I got the proper gear for the t-case before I started calculating the mpg I am getting.
And to be honest as long as my XJ is running solid the mileage it is getting really doesn't concern me.
And to be honest as long as my XJ is running solid the mileage it is getting really doesn't concern me.
Thread Starter
Junior Member
Joined: Jan 2015
Posts: 61
Likes: 0
From: Germany
Year: 1990
Model: Cherokee
Engine: 4.0
Cap, rotor and wires changed also the plugs now. The t-stat may be the same but the gasket is the problem and the degrees when the t-stat opens.
Need to find new o2 sensor from NGK....
NGK plugs are available here
Need to find new o2 sensor from NGK....
NGK plugs are available here
Senior Member
Joined: Mar 2012
Posts: 974
Likes: 14
From: Racine, WI
Year: 1997
Model: Cherokee
Engine: 4.0
Maybe I missed it in all of these posted I did not see anywhere the op said how he calculated his mileage without changing the speed-o-gearing to be an accurate 11.5 mpg. I don't know what the mathematical equation would be to figure the true mileage after putting on taller tires? I waited until I got the proper gear for the t-case before I started calculating the mpg I am getting.
And to be honest as long as my XJ is running solid the mileage it is getting really doesn't concern me.
And to be honest as long as my XJ is running solid the mileage it is getting really doesn't concern me.
I didn't see anyone mention this, and it's quite important.
You have 31" tires but said nothing about changing your speedometer gear to compensate, nor did you mention compensating for the increased tire diameter mathematically when calculating MPG.
With 31's, you're traveling 10% farther/faster than your odometer/speedometer are telling you.
Changing your speedo gear is very easy -- http://go.jeep-xj.info/HowtoSpeedoGears.htm.
You have 31" tires but said nothing about changing your speedometer gear to compensate, nor did you mention compensating for the increased tire diameter mathematically when calculating MPG.
With 31's, you're traveling 10% farther/faster than your odometer/speedometer are telling you.
Changing your speedo gear is very easy -- http://go.jeep-xj.info/HowtoSpeedoGears.htm.
::CF Moderator::
Joined: Aug 2011
Posts: 43,971
Likes: 1,578
From: Prescott, Az
Year: 1990
Model: Cherokee (XJ)
Engine: 4.0
Actually, the O2 sensor is NTK, which is part of NGK.
Herp Derp Jerp
Joined: Nov 2011
Posts: 18,251
Likes: 17
From: Parham, ON
Year: 1999
Model: Cherokee
Engine: 4.0L OBD-II
Thread Starter
Junior Member
Joined: Jan 2015
Posts: 61
Likes: 0
From: Germany
Year: 1990
Model: Cherokee
Engine: 4.0
will check the grounds tomorrow and the relays (O2 sensor relay the most :-))
and clean all up. I will take pictures and post them here to figure out where my problem could be...
A new O2 sensor is installed, will try to messure the wires as it is written here:
http://www.naxja.org/forum/showthrea...ht=sensor+test
and clean all up. I will take pictures and post them here to figure out where my problem could be...
A new O2 sensor is installed, will try to messure the wires as it is written here:
http://www.naxja.org/forum/showthrea...ht=sensor+test