wa9yor68

97 xj 4.0l new exhaust header &o2 sensor.previous header had a crack at the collector.starts fine & runs ok until it goes into closed loop. then can hear a slight change in intake air as IAC changes. vacuum falls from 17 in. to 13 in., runs rough then shows 171 code.runs extremely rich.have checked for vacuum leaks including plugging vacuum port that goes to charcoal canister and other places. new iac & tps.next step is to blow propane around manifold to see if anything changes.also, O2 sensor volts hover around .22 volts with slight increase as throttle in goosed. help please

CCKen

How do you know it's running extremely rich?



P0171-1/1 FUEL SYSTEM LEAN

Here's some 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

Is your fuel pump pressure okay?

Don't have the PDC layout available right now, but you could check the mini fuses one at a time to see if you have a blown O2S heaters fuse.

Check the upstream O2S wiring as it passes over the intake manifold for chafing through the loom and to the wiring within. Check the downstream O2S wiring for being ate up by the driveshaft.

wa9yor68

black exhaust & can tell by smell, also burns eyes- wiring to o2 sensor is ok, already checked at plug-apparently o2 sensor is sending lean sig to cpu & cpu enriches fuel to compensate- gotta get a fuel pressure gauge tomorrow& check that-the o2 sensor i used is a ngk 23151,i believe it's the right one-sure has me stumped-maybe the cpu? because it runs good in open loop but no good as soon as all the sensors come into play