4.7HO P0171 will not go away (lean bank 1) - gas out exhaust - JeepForum.com
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Unread 10-25-2009, 05:43 PM   #1
Reiver
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4.7HO P0171 will not go away (lean bank 1) - gas out exhaust

Hello,
I have been working on this every day for 3 weeks or so. First I had some evap system codes...found a hose in the back - fixed it. However, I still have the P0171 code. The fuel trims keep going out of whack. Replaced the 02 sensor twice (the foul exhaust ruined them) and the plugs as well. Replaced TPS just because I already had one. New Airfilter. New tank of Chevron Premium. Seafoamed the crap out of it (TB, Vacuum line, gas and oil - changing the oil about 30 miles afterwards)

Q: I have 4 fuel trim readings and one gas line....what the hay? Can someone please explain? I have spent a week or more on google/bing/forums
I have bad fuel trims (one way positive, one way negative %) on Trims 3 and 4. I have reset the computer by unplugging the battery multiple times after working on an area to no avail to bring the long term back to 0%

I also replace PCV.

Runs rough even on cold start-up when in open-loop and still when it warms up. Runs better cruising down the road, but throws p0171 the second I come back to idle - like pulling over, stop sign or light (or just letting it warm up in driveway)

I am about to beat my head into the driveway. I have worked on it up to 13 hours a day. It's not for lack of effort - pls help!

P.S. Checked Compression - Good. Fuel Pressure 50PSI on rail and 51-53 when idling

2003 WJ 4.7HO <<<

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Unread 10-25-2009, 06:17 PM   #2
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Quote:
Originally Posted by Reiver View Post
Hello,
............

The fuel trims keep going out of whack. Replaced the 02 sensor twice (the foul exhaust ruined them) and the plugs as well.
.............

Q: I have 4 fuel trim readings and one gas line....what the hay? Can someone please explain? I have spent a week or more on google/bing/forums
I have bad fuel trims (one way positive, one way negative %) on Trims 3 and 4.
.............

2003 WJ 4.7HO <<<
Since you have 4 O2 sensors, it doesn't do any good to tell us that you "replaced the O2 sensor twice." Which of the 4 O2 sensors did you replace????

There are short term fuel trims and long term fuel trims, and you have one of each for each bank of cylinders, that's 4 trim readings.
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Unread 10-25-2009, 06:36 PM   #3
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I replaced the upstream o2 sensor on bank 1 (the bank thowing the code) which regulates the a/f mixture from my understanding (the first time i got the p0171 it had a pending o2 sensor sensor 1 bank1 slow to respond) I replaced since it was covered with black soot, just like the spark plugs

Thanks!!
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Unread 10-25-2009, 07:56 PM   #4
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I thought that this sounded familiar, and after checking, I see you have an earlier thread on this same subject. I can only give you the same advice here that I did in the other thread; take out the bank 1 fuel injectors and have them checked. Apparently you haven't done this yet.

If you don't want to pull the injectors, there is a somewhat imperfect alternative. Unplug the electrical connection to one of the injectors in bank 1, and then drive and/or let the engine idle for a while. If that injector is a problem, then the bank 1 long fuel trim should improve (assuming that the O2 sensors are still ok). Reconnect the injector; then unplug another one and again see if the fuel trim improves. Continue in this way to check the remaining bank 1 injectors. Of course killing one of the cylinders will contribute to rough running, but you have that problem already. Also expect another code to be thrown.
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Unread 10-25-2009, 09:12 PM   #5
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Thanks - I will try just unplugging and running - I ran another test (too many tests to mention - and didn't mention) on the injectors - I don't remember if from Jeep Service Manual or another resource. I did also forget to mention that turn on the a/c makes it run even rougher when it's cold.

Also, I don't know which is bank 1 long term fuel trim (I'm guessing 3 & 4) since I have 4 fuel trims
3 & 4 now show -100.6% on both long and short term

Thanks!!
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Unread 10-25-2009, 10:26 PM   #6
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On second thought unplugging the injectors one by one might not be very helpful in the case of a leaking injectors. If one is leaking, it will do so whether there is power applied to it or not.

What would probably work would be to substitute a known good injector for each of the other bank 1 injectors, one at a time, while checking the long term fuel trim after each substitution.

BTW, have you looked at each spark plug in bank 1? The cylinder or cylinders with leaking injectors should be very sooty.
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Unread 10-25-2009, 11:27 PM   #7
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Yes, all 4 spark plugs were covered in soot...I replaced - same with the o2
I did the test - the only problem is the fuel system goes into open loop mode and sets the default fuel trims
I removed the first three, but the last on the bank's connector feels like it's glued on now...I move the side clip back and nothing - oh, well - I've burned my hands enough tonight...will try again when the engine is cool.

I will try swapping an injector from the other bank (one at a time) when I get off work tomorrrow

P.S. I've also doused all the vacuum lines / intake manifold, etc with water to try and find a leak - no luck there

When I did your test....the bad smelling exhaust went away...it came back when I plugged them all back in again (and fuel system was in closed loop)

The default fuel map from the computer creates:
Long Term Trim 1 = 0%
Long Term Trim 2 = 0%
Long Term Trim 3 = -38.6%
Long Term Trim 4 = -45.2%

It will not budge from there (after it moves in that direction) no matter how long it runs
(and I would erase codes to get new dtc's so that I'd get a current freeze frame)

I figured all of them would be 0% for default computer values
Also, are fuel trims 1-4 one for each of the cylinders on that bank? (since the code is for that bank)
I can't find in the service manual or anywhere else what the 4 fuel trims exactly map to

Thanks again!!!
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Unread 10-26-2009, 08:51 AM   #8
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Does this model have MAF sensor? It should be a square shaped piece on the intake tube. Sometimes they get dirty (from aftermarket oiled air filter elements) or fail (age, Q.C.). I'm not sure if 03's had them or not but it might be worth a look. They sell MAF cleaner at most autopart stores.
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Unread 10-26-2009, 10:00 AM   #9
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ZJs/WJs don't use a MAF sensor.
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Unread 10-26-2009, 10:49 AM   #10
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Yeah, we just have a MAP sensor...which is the most difficult sensor location I have seen (behind alternator/compressor mounting block - very hard to get a torx in there even with l-shape...need an even longer set of 90 degree torx wrenches
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Unread 10-26-2009, 01:47 PM   #11
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You have been receiving conflicting signals or information. The P0171 indicates that the mixture is lean, but the sooty plugs and gas out the exhaust say that it is rich. It appears to me now that the O2 sensor signal (which causes the P0171) is the bad info. Something is happening to make the sensor signal indicate excess air. Maybe air is getting into the exhaust system at some point in front of the sensor or even at the sensor position. In other words, there might be a leak letting air into in the exhaust system at or in front of the bank 1 upstream O2 sensor. Double check to make sure the O2 sensor is screwed in properly and look for possible exhaust manifold or pipe leaks.

However, significant confusion comes from the fact that you are getting large negative fuel trims. Negative fuel trims result when the PCM shortens the injector pulse widths. That is, when the PCM calls for less fuel to be injected. If the mixture is actually lean (P0171), the PCM will try to inject more fuel than usual and positive fuel trims would be created. Your measured negative fuel trims is opposite of what the P0171 calls for and contradicts the evidence that too much fuel is being injected. The fuel trim values you get are a mystery to me.
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Unread 10-26-2009, 04:01 PM   #12
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I've been wondering if the PCM is going out....it's a mystery to me which is why I'm so determined
I need to get a serial cable for my laptop instead of the dummy generic scanner I have now so I can monitor in real time and check fuel trims at idle, 1500 rpms, and 2500 rpms. I've looked for exhaust leaks pre-upstream o2 and haven't found any. I've also put the o2 in multiple times (new) plus pulled it out and checked to make sure it's not leaking around the sensor.

The problem only seems to really occur at idle - the computer won't throw a code until I idle and the fuel trims normalize if I drive back and forth on the toll road at 65mph for 30-45 mins....the second I go to a stop sign (even though it's not really running rough at that point - only after it idles for a bit) it throws that code.

Driving me mad...my brother-in-law needs to move out (been living here for 4.5 years) and just waiting on the Jeep to be fixed to pull a trailer to the next town ;-p
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Unread 10-27-2009, 05:00 PM   #13
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My wife got tired of my working on it and brought it to the dealer - she just called because they claimed o2 sensor - although I've replaced twice with mopar....She told them to go back and try again...Waste of $100
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Unread 10-27-2009, 05:55 PM   #14
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The dealer claimed o2 sensor - my wife pulled out the previous o2s - they benchmarked fine...the tried to diagnose for another couple of hours and then couldn't figure it out. She didn't pay anything for the diagnosis and they verified my o2 sensor is actually good after all. So much for taking it to the pros...
I would be but the jeep is still
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Unread 10-27-2009, 09:00 PM   #15
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I have no idea what exactly the dealership did - but the Jeep after returning now idles at 1900RPMs, throws o2 sensor errors, lean condition bank 1, and spews gas out the exhaust (much worse than before)...I'm out for blood....5 star service, my ***
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