Most of the time my jeep does terrible on gas. Ive done the math and I get about 6-8mpg. When I get poor mpg the it also just dumps black smoke out the exhaust when accelerating. Also idles rough. Then sometimes itll run better, no smoke, and better mpg. I have a new bosch o2 sensor in, and a duralast TPS. There is also a small leak before the cat. I Do have a check engine light that said it was running too lean, i dont remember the code but ill go grab it again in a minute. Anyone have any advice? Im just trying to get it running right because im trying to sell it. thanks in advance.

 

codes are
p0171 (system too lean bank 1)
p0138 (o2sensor circuit high, coltage back 1 sensor 2),
p0131 (o2 sensor circuit low, voltage back 1 sensor 1)

 

O2 sensor. Check the fuse. If it's good, replace the upstream O2 sensor(s).

 

What fuse/where and what part number/brand O2S. I don't think the OP has said what year Heep he/she has, although it would appear to be an OBDII Heep.

 

He gave a little bit of information, I gave a little bit of information. That's how that works.

 

I did the math one time... had bad gas mileage. ..
Turns out my neighbor was stealing my gas.
For like 3 months...
A little at a time.

Gremlins.

 

Fix the exhaust leak. That alone will screw with an O2 sensor. If fixing the leak doesnt clear your codes, then the sensors may be it. Check the fuel pressure and for any vacuum leaks just to be sure.

 

upstream tells pcm if it thinks it's running lean.leak before cat probably not an issue in this case(fix it anyway).02 sensor replaced was bosch,upstream or downstream?upstream pull the bosch and replace with ntk.just went through the same thing.