jvepp

Hi all,

My 1998 xj 4.0 idles rough once it gets up to operating temperature, and when I drive it, it gets horrible gas mileage. It's throwing the code P0171. Any suggestions on what to check?

My Jeep was running fine until the freeze plugs started leaking, so I put some bars stop leak in and topped off the coolant. I started adding the stop leak when the engine was cold, but once it got to operating temperature (about 210 degrees) it started to idle rough. I tried to drive it and it stalled out at a red light and it took quite a few cranks to get it going again (definitely wasn't a battery issue, lights didn't dim and it was cranking strong). That's when the code popped up. Its been sitting in my driveway ever since, and whenever I go to run it, it will idle fine until it gets to operating temperature, then it will start to idle poorly. Also a lot of exhaust comes out of the tailpipe, which leads me to believe the computer is dumping way too much fuel in the engine.

What stumps me is that it was perfectly fine until I put that stop leak in it, then all of a sudden it won't idle right. If it helps here's the freeze frame data that my scan gauge displayed:

I looked up P0171, and if could be anything from a cracked manifold to dirty injectors. I just need help narrowing it down. I'm guessing o2 sensors, but the current ones are fighting me to come off.

Given my situation, any other suggestions on what could be the cause?

Thank you!

CCKen

Is that (-) 32.8 or (+) 32.8 on the STFT? In either case it's WAY out of spec. So is LTFT.

I normally see load around 5% at idle. I see it's at 17.4 RPM. I take it that's 1,740 RPM.

Try checking the readings at idle, then at 2,500 RPM to see if the STFT moves towards zero and the LTFT moves towards zero. If it does, a fuel injector may be leaking.

Is the upstream O2S cycling every 2 seconds?

This is one sick puppy.

jvepp

It doesn't designate the fuel trims + or -. I would assume positive because its trying to compensate for the lean AFR it thinks it's seeing.

Unfortunately my scan cause doesn't have the monitoring option, it can only display freeze frame data. I don't think I am able to monitor the o2 sensor either, but I will check.

Also the engine rpm was a typo. I meant to type in 704 rpm.

Thank you for the help! It is much appreciated

CCKen

What kind of scanner do you have? The freeze frame must be coming from live data so I would think you could access it (?)

Generally, a scanner will show a (-) sign in front of the STFT correction number if the PCM is pulling fuel off so I think, based on the DTC code 171, you are seeing a (+) correction.

If you can check it again, only this time advance the throttle to 2,500 RPM and capture the freeze frame. If the STFT fuel correction drops to a lower value it could be a dripping fuel injector.

In any case, review the diagnostic data below. There's lots of things you can check.

I think you should consider that the ECT Sensor may be contaminated (coated) by that bars stop leak you added, in that the engine was running okay until you added this stuff. You would have to remove the ECT Sensor and examine it.

P0171-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

jvepp

I have the Innova 3150d scan gauge. I am fairly certain it can only display freeze frame data.

I was checking for codes again today, and and new code popped up! p0138 (o2 circuit high voltage bank 1, sensor 2). I think this is my issue. I will try to replace the downstream o2 sensor and go from there. (I've tried in the past to take it off but that sucker is on tight!!!)

Also, I just noticed that you are pretty close to me! I am located in Ann Arbor, and Canton is right down the road.

jvepp

Whelp I tried taking off the downstream o2 sensor, but it is very stuck, and I ended up partially tearing the bung off of the cat, so now I need a new cat as well...

CCKen

I just read the Innova 3150 d Owner's manual and it doesn't mention viewing live data. It looks like this device is an advanced code reader only.

Yes indeed...Canton. Just as cold as A2. Hope you're working in a garage.

jvepp

Haha I wish... My jeep is sitting in my driveway. I've decided to wait until it's warmer to tackle the catalytic converter.

CCKen

I know what you mean. I'm waiting for Spring to change my exhaust system.

Jameswest21

Try running some sea foam through the intake manifold of your brake booster. It's less than 10 bucks a can and couldn't hurt. If you need to look it up just type it year and model into YouTube it will show you

jvepp

Well I put the new catalytic converter in along with new o2 sensors. I go to start it up aaaand it won't start. It cranked a few times then stopped. It felt like a dead battery so I put a charger on it and still nothing. Now when I try to turn it over there is a loud singular clicking noise, no cranking at all.

I'm just thinking it was too cold for the Jeep to start (it was right around 0*F), which is dumb because I intended to drive this car through the winter, which is probably not going to happen. I leave for college on Saturday so I won't have a chance to look at it probably until the spring.

Frankly I am getting very tired of all these issues from this Jeep, and I'm entertaining the idea of selling it. If anyone in the Ann Arbor/Detroit area wants a Jeep with very little rust that doesn't run, hit me up.