I think I will be replacing my O2 sensors to seek better mpg than I am getting right now. I still need to check my 15 amp heater fuse but I'm not sure what else could be causing my low mpg. I'm at almost 97k, I have brand new 235 tires and take it easy of the gas pedal. I have seafoamed the gas twice. The engine seems to run great and I am not getting any check engine light.

Anyone have the proper part number and/or recommendations on how to get the new 02 sensors on and off?

Heat is your friend. Either use a torch on the pipe around the sensor (NOT ON THE SENSOR!) or run it until it's up to full temperature.

I get around 18 with 235s. You definitely have something wrong.

Friction? How are your wheel bearings? Do they spin freely?

If you replace O2 sensor, get the NGK.

If your 02 heater fuse is blown, you likely will have a check engine light with multiple codes with the word oxygen sensor "heater" in the description. Doesn't sound like that is your issue.

I absolutely agree with 4WDFOREVER, you should use ONLY NTK oxygen sensors. They are the original equipment on your XJ and will work the best. They are very widely available online and at parts stores. Check around.

At 97K, if these are the original oxygen sensors, they should be replaced. Period. These sensors have a finite lifespan.

Also, be sure that your tuneup hardware is fresh. The importance of those parts cannot be overstated. Fresh Champion copper plugs, quality plug wires, distributor cap and rotor.

Lost my optimum mpg during a 600+ mile round trip the summer before last. No CEL. Rough figure was 13mpg. Replaced both O2 sensors (with no problems) using the NGK brand which is the OEM brand used. Been good to go since. Make sure to wire tie the harness out of harms way when done installing them.

I think my wheel bearings are okay, my front left is new, my front right is still "good" as told by the mechanic. Although I do have a Timken hub/bearing assembly that I should go ahead and get put on. RPMs are normal so that may rule out most of the friction possibility, I would think at least.

I'm seeing recommendations for both NGK and NTK. Typo? Or are they different brands? Thanks

I'm almost out of gas after putting in 10 gallons and only driving 105 miles...terrible.

Found the part number on the NGK (same as NTK) website. Here it is in case anyone else ever looks this up.

Part # 23151 - Upstream (B1S1)
# 23099 - Downstream (B1S2)

NTK/NGK = same.

Post when you solve problem, please.

I only mentioned wheel bearings because that was the problem I had on one of my secondary vehicles. New bearings, mpg went right back to where it should have been.

Any pointers for performing the 02 sensor change for a 98?

Upstream = before Cat Converter
Downstream = after Cat Converter, correct?

I will warm up the engine first, then unplug battery, then get to unscrewing the 02 (once I find them). Hopefully they will come off without much trouble.

Upstream = before Cat Converter
Downstream = after Cat Converter, correct?

Yep. You should use the proper tool for removing them. It can be rented free at your local Advance Auto(maybe others?). You buy it then get a full refund. Make sure you fasten the wiring to where they can't be damaged after installation.

The right tool is key. You can rent it from your auto parts store or do like I did and just get under the jeep in the parking lot. Saved me the fee for renting them and it doesn't take that long. You can't miss them.

Could be cheap gas,Not all gas brands are the same and the cheaper ones don't burn as fully as others can.Driving habits are a big thing so is not carrying around a extra 200lbs of stuff you don't need.

Best part about lower mpg is, can be a number of things. Bad o2 sensors will cause it. Older plugs. Injectors. Partially blocked exhaust system, bad cats or muffler. For the o2s, you reall ly don't need the tool if you can't get it in hand. I used an open wrench and channel locks every time I've changed em and never had an issue. And like someone else said. cheap gas makes a difference too depending where you live. Hope you can figure it out as this is always an issue brought up on here.

*sigh*

Cheap gas is not going to take a good running vehicle from 17-18 MPG down to 12-13 MPG.

Something is wrong with his vehicle. The problem needs to be found and fixed. It's not his driving habits, it's not his gas, it's not the junk he's carrying around.

When I worked in the shop, way back when, LOL, the first thing we would do when someone complained about fuel economy...we would pull out the 5 gas analyzer and look at what was actually coming out of the tailpipe....then go from there.