hicj7

Thanks in advance for your viewing this thread! I have been chasing down run ability problems for some time now. My 99 Cherokee was running poorly and had oxygen sensor problems (P0132, P0135, P0171 and others). I replaced both sensors with OE fit Bosch sensors and reset codes. I continued to get those codes when I found a fuse in the PDC fuse box I believed to be related to the O2 sensors heater circuit and replaced it. I reset the codes and drove it. The Jeep is still running poorly, it has been getting about 8 MPG, and has a code P0171 (along with a P0740, but I believe it to be unrelated). Code P0171 is:
"System Too Lean (Bank 1)
Im having a hard time figuring out what is going on! Two new sensors, Ignition is in good (new) condition, sprayed Throttle body cleaner around intake and vacuum hoses looking for a leak, and tested the fuel pressure (reading 48 psi with an acceptable range of 42psi to 54 psi)...
Any ideas would be appreciated!

tjwalker

Check your exhaust manifold. They often crack and that can lead to that code.

Question though....was that oxygen sensor heater circuit fuse blown that you replaced?

hicj7

As i was reading up on the code(s), one of the suggestions was to check some of the fuses. This fuse was in the relays and fuses that were underhood. The fuses weren't clearly marked either on the fuse box its self or in the owners manual. I was lead to believe that it was related to my oxygen sensor heater circuit, and i did get rid of the O2 sensor heater circuit codes that I had present.

RussImsland

lurched and snatched at low speed,missed at high speed,poor mileage.50 bucks for a new throttle position sensor cleared up the problem.

CCKen

FSM says P0171 is A lean air/fuel mixture has been indicated by an
abnormally rich correction factor.

The TPS, MAP, and ECT listed below are the prime suspects.

Here's some possible causes for P0171 from the 2001 FSM:

RESTRICTED FUEL SUPPLY LINE
FUEL PUMP INLET STRAINER PLUGGED
FUEL PUMP MODULE
O2 SENSOR
O2 SENSOR SIGNAL CIRCUIT SHORTED TO GROUND
O2 SENSOR HEATER OPERATION
TPS VOLTAGE GREATER THAN 0.92 VOLTS WITH THROTTLE CLOSED
TP SENSOR SWEEP
MAP SENSOR OPERATION
ECT SENSOR OPERATION
ENGINE MECHANICAL PROBLEM
FUEL FILTER/PRESSURE REGULATOR (HIGH)
PCM

hicj7

Thanks to the last two posters to this thread! I replaced both sensors, fuel pressure at the rail was 48 psi, vacuum at the manifold was 18 inches at idle, the exhaust manifold was cracked but symptoms persisted after replacement, at the dealer now...

Houston Kid

Did you ever find the cause? Mine is doing the exact same thing.

Houston Kid

New O2 sensors front and rear fixed my issues.

ASA-Z33

Hey guys,

Having this same issue and getting extremely frustrated. Have new O2 sensors, new fuel pump, recently replaced the tps AND the IAC sensors.

After doing the IAC all was good for about 10 miles. (Would previously start to idle bad after about 20 seconds). Running out of ideas.

Getting ready to replace the ECT and cross my fingers. Similar to the OP I have a 98 xj 4.0.

Thoughts? Any help really appreciated, really starting to get frustrated.

Thanks

-Alex

ASA-Z33

Hey guys-bump

I know I am resurrecting an old thread here but the solutions I tried listed here and came up dry - picked up the ECT sensor today but have not had a chance to put it in.

If anyone has any other ideas for this code please let me know. I also have an APN header that is crack free. I know it's not a vacuum leak as well - I went through possibilities there.

Thanks in advance guys.

- Alex

ASA-Z33

Bump. Replaced the ETC. No dice. Figured that was a long shot anyways. Runs fine for the first minute or so and then starts to idle rough/run rough.

It's going through so much fuel you can smell it at stop lights.

Appreciate any guidance I can get.

skife

When you replaced the sensors, did you put the upstream in the downstream by chance?

ASA-Z33

You mean the o2 sensors? Had a shop do it a few months ago. They are good. Had those done months ago. This issue is recent.

hicj7

For me, it ended up being the exhaust manifold. In saying that, I later had similar problems that ended up being the oxygen sensor. the cheap one I bought on eBay worked for a month, even the Bosch O2 sensor didnt work right. It took a O2 sensor from the dealer to fix the problem. Soooo, make sure your manifold is intact! Mine had a crack at the collector. Make sure your using a good O2 sensor...

ASA-Z33

Appreciate it. Exhaust mani is good. Been through that debacle 4 times( and 4 manifolds), all to familiar with the problems and symptoms there.

Fixed it yesterday - don't know if it was just a crap upstream sensor or if I fouled it off-roading or it got hit with something but that was the problem.

Got a replacement under warranty and Jeepy is all good now.

Thank god. Since the fuel pump and O2s were new I didn't even bother to check them. Dropped a bunch of coin on the wrong parts as a result. Lesson learned.

-Alex