obd II code driveing me nuts

long story ....kid does not listen to driving instructions and sink 98 cherokee 4.0 auto up to the cup holders in water ...after draining her changing some fluits and resting the computer it drove fine exept for a airbag light that i can live with.. but every week or some times every 3 hours of drive time it starts running rough at idle and the black smoke starts... the only code it trowes is a P0171. any idea what the heck causes this .... i tryed the internet and it says its running lean ...i beg to differ ...very rich ....like half a tank of gas in two hours on a trail ride before i decided to disoc the bat and reset the puter and fine for the next week....grrr.. please help thanks for your time

i had similar problem with my 97, after a TPS (Throttle Position Sensor) and a IAC (Idle Air Control) it ran fine for a short 3 weeks. Took it to a garage and it turns out my replacement TPS was bad AGAIN it was reading 0-9 as opposed to 0-100 like it should have. So they grabbed a $20 junkyard part and threw it in at no charge since I originally took it in to "clear codes." Now mines running like new again, aside from needing a trans fluid/filter change. So with that being said, I would test you TPS and possibly replace it.

P0171 is the upstream Oxygen sensor reading too lean.

Because the sensor is reading too lean, the computer is trying to dump more and more gas into the engine. Sounds like a common failure mode for O2 sensors. They don't like getting quenched in water when they are hot.

Oxygen sensors measure just that, oxygen. Low voltages are read as lean, higher voltages toward .9V consistently would be considered rich. Problem is unburned fuel from a misfire will have a high oxygen content and be read as lean. Depending on how smart your particular pcm is, you could have a gross misfire that's not throwing a misfire code, only a lean code. I would check for a wet distributor cap or plug wires and give the coil connector a good once-over.

hubs97xj said:

P0171 is the upstream Oxygen sensor reading too lean.

Click to expand...

sorry what do you mean by up stream....the one in the manifold cause the one behind the cat has be changed since this issue thanks . i just want to be clear

Yep, the one up by the manifold.

Type "P0171 site:naxja.org" into Google, and you'll get a number of threads on here with the same code and some troubleshooting info.

If the sensor is telling the computer the mixture is lean, it will dump more fuel in, resulting in it running very rich, despite the OBD code indicating lean. I'd suspect the sensor, although it could be a number of other things.

Or at least I think that's how it works. Someone who knows more is welcome to throw their 2 cents in.

thanks guys i will swap it out ans see what happens