[90Notch306]

I just picked up a 98 XJ and the gas mileage is horrible. Put $20 in it and went 70 miles. CEL was on and i had it scanned. Bank 1 sensor 2 O2 sensor high voltage. Replaced the downstream O2 and everything was good for 10 miles now the light is back on. The truck runs good though. Before and after i changed the sensor. Seems rich though. Has some black smoke out the exhaust when i step on it. Ive been searching around for the last couple of hours about this. Everything i read is about it chugging though. Mine runs and idles fine. Will the coolant temp sensor throw a CEL?? Any other ideas??

 

[Dylan]

i thought bank 1 is the upstream sensor.

 

[tom tom]

try looking at www.naxja.org

 

[90Notch306]

i thought bank 1 is the upstream sensor.

Its a possibility im not 100% sure its the downstream. But the PO said it was the downstream one. And a mechanic also told me the same thing

 

[90Notch306]

try looking at www.naxja.org

I also have this posted over there

 

[ajmorell]

The downstream doesn't control fuel delivery, only the upstream does. I'd be willing to bet that's your problem.

 

[90Notch306]

Thanks for the input. Does anyone know for sure which O2 is bank 1 sensor 2?

 

[1988JeepXj]

Coolant temp sensor could throw the light if it malfunctioned completely, I would check the codes again, or maybe try to see if you can get somebody to look at streaming data.
I don't know if Autozone has that capability or not.

 

[90Notch306]

Yea ill will be checking the codes again tomorrow. I thing autozone just has a cheap actron scanner too.

 

[NSmist]

Quite possibly your front sensor. Are you getting any kind of hesitation when you hit the gas?

While your at it, when's the last time it was tuned up? What do your fluids look like as well as you're ignition parts? Those can play a good part into mileage too.

 

[90Notch306]

No hesitation at all. It runs great just has some black smoke when im on it and only gets 9mpg. Plugs, wires, cap, and rotor have all been done recently. Fluids are also all clean. It is a mechanicly sound truck except for this problem

 

[ajmorell]

Bank 1 is the upstream sensor.

 

[1988JeepXj]

My service material says for '98 the downstream sensor is bank 1, sensor 2 (1/2 HO2S). The upstream sensor is bank 1 sensor 1 (1/1 HO2S).

It may still be a problem with the upstream sensor, but that code is for the downstream.

 

[whyme86]

No hesitation at all. It runs great just has some black smoke when im on it and only gets 9mpg. Plugs, wires, cap, and rotor have all been done recently. Fluids are also all clean. It is a mechanicly sound truck except for this problem

the problem is your running the wrong fuel in it if its blowing black smoke its prob a diesel :teehee:

 

[Dylan]

i had to think about this again LOL. the cherokee only has one pair of o2 sensors (banks) sensor 1 is up and sensor 2 is down. TJ's (and other vehicals) may have 2 pairs (so bank 1 and 2) and sensor 1 (before cat) and 2 (after).

Just because you get a code that says bank 1 sensor 2 voltage high doesn't mean its a bad sensor. Best thing is like mentioned before, check the actual voltage with a scan tool of all your sensors. especial upstream 02, tps, map, IAT. See where the extra fuel is coming from.

90% of the time if you are not getting any other sensor codes, its the upstream O2 sensor. Its telling the motor the engine is lean and adding more fuel but will not trip a code.

 

[ajmorell]

i had to think about this again LOL. the cherokee only has one pair of o2 sensors (banks) sensor 1 is up and sensor 2 is down. TJ's (and other vehicals) may have 2 pairs (so bank 1 and 2) and sensor 1 (before cat) and 2 (after).

Just because you get a code that says bank 1 sensor 2 voltage high doesn't mean its a bad sensor. Best thing is like mentioned before, check the actual voltage with a scan tool of all your sensors. especial upstream 02, tps, map, IAT. See where the extra fuel is coming from.

90% of the time if you are not getting any other sensor codes, its the upstream O2 sensor. Its telling the motor the engine is lean and adding more fuel but will not trip a code.

I forgot that they started putting 4 sensors on some of the vehicles. I don't think that was the case in 98 though, unless they did it to XJs and not ZJs or something dumb (not ruling that out). I agree about the upstream sensor though, usually they drift a long ways before they throw a code, if they even throw a code at all. I had my upstream drift so far that my ZJ almost wouldn't run and it didn't throw a code.

 

[90Notch306]

My service material says for '98 the downstream sensor is bank 1, sensor 2 (1/2 HO2S). The upstream sensor is bank 1 sensor 1 (1/1 HO2S).

It may still be a problem with the upstream sensor, but that code is for the downstream.

Yes bank 1 sensor 2 is the downstream. I just had it scanned again and that code is gone so the sensor was bad. But now i have a code that says bank 1 system too lean. Any ideas? Still think the upstream sensor is bad?

 

[kargod]

How badly cracked is your exhaust manifold?

 

[90Notch306]

Its not. Its a new pace setter full length

 

[90Notch306]

error code is p0171