I plan to test my cats this week with a vacuum gauge attached to one of the upstream o2 ports. I am suspecting that there may be backpressure issue with some or all 3 of the cats on this 2001. Reason is poor gas mileage. Drives fine, plenty of power, but after replacing the spark plugs, cleaning TB, oil change, CAI, new O2 sensors, and misc maintenance, I am only getting 15-16 MPG.

3 Cats, thats 2 too many for a Jeep that isn't in CA. Anyone with a 2001 XJ that has modified the exhaust give me some info?

NOTE: I will run a legal setup with a state/fed required cat. But 3 is overkill.

Will try and rent a gauge from autozone today, or borrow one.



K

 

Yea best not to mess with the cats cause it will make the computer do funny things. When you say 15-16mpg is that highway or city? Sounds about right for a modded jeep like yours and it really depends on how you drive. I can get 12mpg or 20mpg just from the way i drive

 

If your not popping a code for them then there not broke... and there's not 3... there's two... one for 3 cylinders... the other u think list a cat is a resonator... resonators don't hurt anything flow wise... they just take away any crack and pop that may be left before it gets to the muffler...

And XJ's don't get good gas mileage... looks to me like your in the norm... buy a Geo... lol

 

50/50 city highway. I drive pretty much within the speed limits, and keep the RPM around 2100.




K

 

Resonator? I'll check on the Haynes manual when I get home later. I am no mechanic, so just going by assumption.

Yes, I understand that my Jeep is in the norm. Still want to do whatever I can to squeeze more out of it. This Jeep is not my Daily driver.



K

 

AFAIK the two pre-cats are to assist with cold-startup emissions before the main cat gets hot enough to function. The readings from the o2 sensors after them are essential to the vehicle operating correctly / not throwing a code. You're not going to be able to "trick" the computer into thinking that they are still there when they are not.

This has been covered a lot. The feds don't care if you live in CA or not, if your vehicle came with the emissions a certain way from the factory, it legally cannot be changed from that configuration.