Low emission report = good o2 sensors?

[InvalidUserID]

My 4.0 ZJ Grand Cherokee is getting about 15mpg in mixed city/highway use. Over the past year, I've replaced the plugs, wires, cap, air filter, and the previous owner had replaced the cat. The only other thing I can think of to help would be o2 sensors however my last emission test came back with super low numbers. The HC reading was very low.

My question is since the emissions came back clean, would it be safe to assume the o2 sensors are doing their job and aren't likely to yield any improvement? It's got 195k on the engine and I have no idea when any previous owners replaced them so I'm getting a little itchy to replace them.

 

[CT8]

Maybe, maybe not. New cat and tune up parts. HC is unburned fuel.

 

[HTSS_TR]

With good smog test numbers I would leave O2 sensors alone. Changing a perfectly good O2 sensor for another will not improve gas mileage. Pump up the tires about 4-6 PSI above recommended may yield 2-3% better gas mileage, especially on highway drive you may get 4-5% better. Also, try 1/3 can Lubro-Moly MOS2 at the next oil change, it may improve gas mileage a few percentage.

 

[raytseng]

isn't that about the EPA rating for the car anyway, and the MPG you would have gotten brand new off the factory line?

 

[EdwardC]

Checking out Fuelly, looks like you're pretty close to getting what other people with your model gets:

http://www.fuelly.com/car/jeep/grand_cherokee

 

[InvalidUserID]

Looks like I'm getting what I should then. Thanks for the last link, never heard of that site. I'll have to look into that.

 

[raytseng]

Keep in mind too that these aren't true averages, but data self-selected from people who obsessive track their MPG, so are likely to be from those that are MPG maximizers

 

[Chris142]

My Jeeps o2 sensors got lazy @ around 110K. My power and MPG went way up @ around 95K then dropped off @ 110k. New sensors brought my power and mpg back where it should be.

 

[Leo99]

Save your money in case you need to replace your rear main seal. That's what did in my Jeep 4.0.