2000 Cherokee 4.0L P0171 Code

My 2000 Cherokee stated running rough a couple of times. Almost like not getting enough gas. Put in a bottle of Lucas injector cleaner and drove home. Ran good on the way home, exhaust tone seemed better, even seemed to run much smoother and have more power. As I pulled into my drive way my check engine light came on. Pulled the code P0171 only. Seeing as it has been ages since I replaced my plugs, I pulled them and replaced them. They where really in bad condition, couldn't even see the center electrode in some of them. Looked at the possible causes for a P0171 code, and other then injectors, it would seem most of the potential problem areas would affect both bank 1 & 2 and not just bank one. Please help this old man get his Jeep running right again.
Thanks,
BIll

This code means that the ecu thinks the engine is lean based on whar it sees from the o2 sensor, and has exceeded the trim multiplier (over 33%). So you either have a lean issue(fuel delivery) or a O2 sensor is lying to your ecu.

Low fuel pressure is a common cause. Fuel pump and/or filter.

Yes, start by checking the fuel pressure. You may need to check it while driving to see if it drops. If that is good then proceed to the O2 sensors.

besides low fuel you may be getting too much air. as in a vac leak or a bad map or throttle sensor.

I'd imagine a header crack and/or exhaust leak that's allowing air into the exhaust system is also a possibility. Seems like 4.0's like to crack header tubes like it's fun...

oldbill, where are you at with your jeep, I believe all of the suggestions that have been made are good. Certainly you should verify fuel pressure under load as mentioned as mentioned earlier.

P0171-1/1 FUEL SYSTEM LEAN
POSSIBLE CAUSES

INTERMITTENT CONDITION
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

Check O2S Relays (Heaters) fuse in PDC.

O2S Relays are identified on the lid of the PDC. You can swap the Oxygen Sensor Upstream relay with the A/C Compressor relay and see if the code reappears after two trips.

You can check your TPS. Instructions in pic. Use a safety pin to back probe the connector.

You can test your MAP Sensor.



Example of test::