Long story short, after a complete tune-up almost including plugs, wire, cap, rotor, new CCV, fresh fluid in tranny and diff. My XJ runs smoothly, but the MPG actually drops quite a bit, 11 mpg VS 14 MPG before (the same short commute every day). I figure the problem may lie the cheap aftermarket O sensor I swapped in since so many people emphasize that OEM sensor should always be used.

My question is where I can find this sensor at a reasonable price? The local dealer want $150 for it? I hate to waste my hard earned dollar on greedy stealership. Is there any decent online mopar parts source? The rockauto I normally use does not carry mopar.

 

Your commute must be in town,because 14 mpg is not good either,11 is horrible. The only place to get oem equipment is from the dealership or there supplier. I think your problem is bigger than a 02 sensor.

 

A '99 that gets 11mpg!! I would look into that some more. My '96 with 177,xxx on it gets 18 city, 22 hw.

Do you have a lift?

 

When I got the jeep, it got 14-15 mpg in 100% town driving. After I refreshed almost everything, it got only 11 MPG!!!

What could be wrong, folks, any thoughts?

Could be crank position sensor, I am experience some hard starting sometimes but I thought it may be related anti-drain valve on the fuel pump.

 

I have never had a veichle loose mpg just from changing plugs,without some other sign of poor combustion. It is possible your fuel pump is allowing fuel to drain back,it is also possible the cps,or cam position sensor is the culprit.

 

[QUOTE=Abovetimberline;260460]I have never had a veichle loose mpg just from changing plugs,without some other sign of poor combustion.

I agree, that is why I think the replacement O sensor I used cause this problem.

 

yours has 2 02 sensors,did you replace both of them?

 

As the downstream is only for monitoring CAT.

 

There is a sensor prior to and after cat,the first one is actually the priority as the back one gets it voltage from the front one,the back one does monitor cat as a comparrison to the front one,by comparison it can tell how well the cat is working. You should always check sensors for good operation before you replace them.