I'm relatively certain that my 02 is shot and that is the cause of my low mpg, 18 and dropping. But occasionally while driving there will be a shutter, almost as if the drive train is jumping back and forth. It is a 90 XJ 4.0 5spd. Any thoughts?

 

My 5.2 did the shudder at certain speeds, Oddly enough I replaced the o2 for a diffrent reason and it fixed the shudder also. Not saying it will fix yours, but..... It might, and the 02 should prob be replaced anyway.

 

Not sure about the shudder, but I get 18 when I'm being a good boy.

 

Do you have black tail pipe too?
Black smoke when you hammer it?
Mine does, also has the bucking when you let up on the gas on the hwy.
just curious if your O2 fixes it.

 

the bad o2 sensor is causing the shudder i don't know exactly why it does that but your pre-cat o2 sensor does directly correlate to air/fuel mixture and can make it very confused hence the occasional shudder

 

It does have a black tail pipe. Do I have two o2 sensors? If so should I change them both and with what brand? This is my first jeep so I want to do it right.

 

u got one o2

 

Good to know. Is there a specific brand o2 sensor to buy? I have heard the Bosch sensors don't get along with Jeeps.

 

Bosch for the o2 sensor. Make sure you get the direct fit and not the universal those things suck.

 

So I discovered that the egr relay resistor was unplugged and the wires were crossed. I reset everything back to stock and I'm getting 23 mpg and the shutters have stopped. Going to double check the o2 to be safe.

 

18 miles to the gallon? You've got a darn good jeep right there. I can barely get 17 on the highway pulling 65 MPH!!!