10 MPG.....O2 sensor test

[kastein]

I have been fighting this since I bought the jeep. Currently on 33x12.50s w/ 3.55s and by the odometer I am getting about 11.5mpg. However my speedometer reads about 5 mph slower than what I am actually traveling so I just did a rough estimation by the percent the tire size has changed and figured I am getting around 13mpg but that still seems low to me.

Things I have done:
air filter
plugs
rear 02 (had CEL)

Things I need to do:
fuel filter
front o2 sensor
possibly TPS

All I want is to get 15mpg! Doesn't seem like that much to ask.

You really should regear. 33s on 3.55 ratio is not ideal at all - I should know, I'm on 32s with 3.55 for hopefully only another week or two.

 

[AG74683]

Im having problems with mine as well....

Its getting around 12 MPG around town, which seems way low to me. I was expecting 16-17 when I bought it, right at what my old TJ was getting.

Plugs and Plug wires are pretty new, air filter is clean, no exhaust leaks that I can see...

 

[RadioShackSpecial]

Im having problems with mine as well....

Its getting around 12 MPG around town, which seems way low to me. I was expecting 16-17 when I bought it, right at what my old TJ was getting.

Plugs and Plug wires are pretty new, air filter is clean, no exhaust leaks that I can see...

Engine? Miles? Tire size? Gear ratio? All factors in to the MPG game. :roll:

 

[AG74683]

Engine? Miles? Tire size? Gear ratio? All factors in to the MPG game. :roll:

4.0, 101k, 31" MTRs, gears are stock.

I figured it wouldnt be this bad, even with the stock gears. I was running stock gears in my TJ and it had 32" tires on it.

 

[RadioShackSpecial]

4.0, 101k, 31" MTRs, gears are stock.

I figured it wouldnt be this bad, even with the stock gears. I was running stock gears in my TJ and it had 32" tires on it.

What year is the rig? Factory tow package? You may have 3.07's which would explain the bad mileage.

Or what rpm does she run at for 60mph? Around 2000rpm would be 3.55's with 31" tires.

 

[joe_peters]

XJ MPG articles:



http://www.jpmagazine.com/projectbuild/154_0808_building_a_fuel_efficient_jeep/index.html


http://www.jpmagazine.com/projectbuild/154_0810_building_a_fuel_efficient_jeep_part_2/index.html


http://www.jpmagazine.com/projectbu...cherokee_xj_project_mileage_master/index.html

 

[AG74683]

What year is the rig? Factory tow package? You may have 3.07's which would explain the bad mileage.

Or what rpm does she run at for 60mph? Around 2000rpm would be 3.55's with 31" tires.

Its a 99. I was told it had factory tow. Im gonna check the VIN with a dealership monday and see what they say what options it came with.

It runs probably around 2200-2300 at 60 I believe, I'll have to double check soon.

Oh yeah, one thing Ive found a little strange...it runs below the 210 mark, its around 175-180 degrees usually. Is this normal?

 

[Ecomike]

I just posted an FAQ like "How to test O2 sensors" thread here:


http://www.naxja.org/forum/showthread.php?p=244627865#post244627865

Lets keep the questions here, if you have any please.

 

[Ecomike]

Please delete Error post, wrong thread.

 

[FlexdXJ]

I don't think that an O2 sensor would be responsible for a "big" gas mileage hit.

Are you sure about that? A bad O2 sensor usually causes a pretty decent MPG loss.


Haha, oops old thread!

 

[Ecomike]

Its a 99. I was told it had factory tow. Im gonna check the VIN with a dealership monday and see what they say what options it came with.

It runs probably around 2200-2300 at 60 I believe, I'll have to double check soon.

Oh yeah, one thing Ive found a little strange...it runs below the 210 mark, its around 175-180 degrees usually. Is this normal?

If you are reading that off the dash gauge, don't trust it, they lie. Get an infra red hand meter and check it at the T-stat housing.

 

[AG74683]

found out today that the XJ has 3.55 gears in it.

 

[Baja_XJ]

I was getting 17-18 highway, Pulled intake and exhaust, replaced gasket and boash O2 sensor, now Im getting 8 on Highway. Checked my Vacuum Lines, they seem to be connected correctly, checked O2, its working properly. What should I check next?

 

[Ecomike]

Year? How many wires on the sensor. Did you get the right OEM sensor?

 

[Baja_XJ]

Its on a 90, I dont remember how many wires, 3 I think, it plugged right in. Its the one autozone pulled up, it looked the same but I know that usually dont mean much

 

[Ecomike]

The check the three wires going to it to see if the large one has 12-14 volts? One should be a real good ground, test it with and ohm meter versus the battery negative post. If either is bad, no ground, or no 12-14 volts you have the problem.

Any possibility you have a manifold leak, intake or exhaust, or cracked exhaust?

 

[Baja_XJ]

I checked it already, it reads good. Whats the next step to check?

 

[Ecomike]

Stuck fuel injector, lean, making other injectors run rich? Bad computer, or bad wire to the computer? Have you run the analog meter test of the live signal from the O2 sensor to the computer?

How to test O2 sensor faq:

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=Oxygen

 

[Baja_XJ]

Its wierd that it got great gas mileage, then I had the intake and exhaust off, put it back together with new gasket, O2 sensor and everything torque to spec and now getting around 8 or 9 MPG if that. So with that said I doubt its the computer, although not ruling it out. I had the fuel rail off and now there is a consistant damp spot on top of the head in the front so Im going to replace the O rings on that injector and try again although I cant hardly believe that one slightly leaky injector could cause a 11MPG drop but I'll seen weirder things before so its worth a try I suppose