I have had this code for a while now and I can not figure it out. My idle is very rough and you can smell gas fumes even inside the cab. For starters Ive changed the upstream o2 sensor and replaced the exhaust mani with a APN header. The CEL went away for a few weeks and then came back. All my header bolts are tight and the intake manifold is seated probably. My fuel pressure reads 48 psi when primed and continues to read that once running. When the problem first started to happen the CEL would come and go and it would some days act up and then for weeks just be normal again. Any help would be appreciated. Ive been all over google but I just cant seem to find a lot of information other then people replacing the o2 sensor and the header.

 

My vehicle is 98 XJ with a 4.0 btw

 

P0171-1/1 FUEL SYSTEM LEAN

When Monitored: With the engine running in closed loop mode, the ambient/battery
temperature above 20 deg. F and altitude below 8000 ft.

Set Condition: If the PCM multiplies short term compensation by long term adaptive and
a certain percentage is exceeded for two trips, a freeze frame is stored, the MIL illuminates
and a trouble code is stored.

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

Things to consider now are:

O2S heater fuse in PDC blown.

TPS Voltage too high - check to see if it is.

 

^thank you for that helpful info

 

Checked all the fuses and changed the tps. Still the same issue.

 

How about rotten out vacuum lines. I would take a good hard look at every line in the engine bay.

 

If you can, try to get the freeze frame data the next time you get the code. Throttle position, fuel trims, and engine RPM would be good to know.

 

I've checked all the vacuum lines pretty thoroughly when I took the intake mani off to put the header on. I didn't see any that were rotten or that stood out.

 

I do not have a scanner for obd II but I will probably pick one up soon

 

I have freeze frame data now but I'm not sure what to look for.

 

Do you have the engine RPMs or fuel trims or throttle position?

 

Here are the two photos from the freeze frame

 

That short Term Fuel Trim is maxed out adding fuel (lean condition). So is LTFT.

Run the RPM up to 2,500 and see what the STFT does.

 

Okay so at 2500 rpms my short term goes to about 6 and long term goes to 0

 

Actually I take that back. When the motor warms up to operating temp both short and long term fuel trim will stay the same as in the picture