CEL P0171 and misfiring - JeepForum.com

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post #1 of 7 Old 11-01-2008, 04:36 PM Thread Starter
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CEL P0171 and misfiring

Hi, I am hoping someone can give me some advice here. I have been away for a month and came back to find the Jeep running very rough. During the time I was away we were hit with a cat 3 hurricane, and everything got wet. Now the Jeep seems to be misfiring, puffing a little black smoke and a small amount of black liquid out the tailpipe, and is displaying the Check engine light with the code P0171. P0171 means Fuel System Lean A lean air/fuel mixture has been indicated by an
abnormally rich correction factor.
From what I understand, many times this is caused by a vacuum leak or bad o2 sensor, but would that cause misfiring, also if I am misfiring, wouldn't I have a code show for what cylinder is misfiring?
I have not seen anyone anywhere even suggest that it could be the spark plugs, but thats what I was kind of thinking could be the problem.
I don't want to have to bring this to a shop because it would be major money here, but I need to fix it soon, I am borrowing my dad's car while he is away, but he will be back soon, and I don't want to have to bum rides to work.

PS The Jeep is a 2002 TJ SE 4cyl, I have no performance or engine mods.
Thank you, I know one of you all can help me.

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post #2 of 7 Old 11-01-2008, 04:40 PM
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Did you check your distributer cap? did you check your fuel and air systems?

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post #3 of 7 Old 11-01-2008, 05:11 PM Thread Starter
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I really don know much about this stuff, what/where is the distributer cap, and what should I be looking for in the air and fuel systems?
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post #4 of 7 Old 11-01-2008, 06:19 PM
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It's over on the passengers side of the engine. I'd say change the plugs wires and distributor cap. Look for some moisture in the intake. Might want to change the O2 sensor too.

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post #5 of 7 Old 07-03-2013, 02:08 PM
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This code means that the upstream O2 sensor was detecting that not enough fuel was being injected (running lean). The possibilities are endless without more information.

Could be as simple as bad O2 sensor.
Could be a bad ECU
Could be a sort or open somewhere in the wiring causing a bad signal to be sent to the ECU
Could be bad or overly dirty injectors
Could be a vacuum leak or something allowing too much air.

I would say do a search on how to check for each of the above problems and post your findings

edit: oops! didnt realize this was such an old thread!

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Last edited by nmcclure7; 07-03-2013 at 02:18 PM.
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post #6 of 7 Old 07-03-2013, 02:19 PM
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If you have access to a scanner you can check the O2 crosscounts with the engine hot.

If you don't, pull the O2 sensor and see if it is all gummed up with soot and burned fuel. This method is far from fool proof, but it's better than nothing.

Definately check for vacuum leaks.

Pull your plugs and inspect for fowling.

Check your air fliter.

Check out your throttle body to see if it needs cleaning.

Pull the distributor cap and check the contacts in it and your rotor fro signs of corrosion or burning.

Yes, that's a lot to check. but, it could be a lot of things causing your issue.

Also, you could have bad gas or water in your fuel.

EDIT: Also, if you don't even know where your distributor cap is you really need to get some type of service manual. The factory manual is best, but if you are lacking basic knowledge, even a Hayne's or Chilton's manual will help.

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post #7 of 7 Old 07-05-2013, 04:46 PM
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I had an odd issue once where my 2000 XJ had a check engine light for cylinder misfire, cant remember the exact wording but I pulled the plugs and one was worn way down, abnormally low. Not sure why I'd had the jeep for a long time already and after replacing the plugs it's been fine ever since.
Weird things can happen.

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