terrible gas mileage & code p0171 - JeepForum.com
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post #1 of 6 Old 10-30-2013, 12:08 PM Thread Starter
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terrible gas mileage & code p0171

I have a 1999 Jeep grand Cherokee Laredo 4wd ... its throwing a check engine light so I went and had it read. The code is p0171 system too lean.. its says a lean air/fuel mixture has been indicated by an abnormally rich correction factor, right rear fuel system lean. The catch is my gas mileage is 4.6mpg (no joke) I have no clue where too start or what exactly is wrong.. can anyone help please & thank u

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post #2 of 6 Old 10-30-2013, 09:54 PM
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1988 YJ Wrangler 
Join Date: Aug 2010
Location: Chesapeake VA
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Are there any other indications on the dash that are weird? Is the CEL and MPG the only indications you have? Does it lack power? Does it sputter when you get into the throttle? Does the thermometer indicate? Need more info.

'88 YJ with SOA and SYE and a bunch of custom crap from BWF in Chesapeake.
'97 XJ on 8" lift, double triangulated rear, long arm 3 link front, Eaton/60 with 5.14 gears.
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post #3 of 6 Old 10-31-2013, 07:21 AM
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2002 KJ Liberty 
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1st what engine,4.0 or 4.7?

Most common cause of that P0171(and/or P0174) is vacuum leaks.

'02 Liberty sitting on 35" tires,HP44,RockJock60,and AtlasII t-case
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post #4 of 6 Old 03-06-2015, 10:45 PM
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Im having this same exact problem, bout 6.8 mpg, an same error code 0171.. HELP MEH!
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post #5 of 6 Old 03-08-2015, 04:01 AM
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2008 KK Liberty 
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Do you have any leaks (hissing) anywhere? Exhaust or intake. Next, I'd get a scan tool and see if my O2 bank 1 sensor 1 was dead/lying/stuck lean. No scan tool? It wouldn't hurt to throw an O2 sensor at it based on the age of the jeep.

You're getting terrible gas mileage because the computer is adding fuel to the bank 1 side of the engine because it "senses" a lean condition from the O2 data it is receiving. Could be adding as much as 30-50% if the O2 fixed lean.
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post #6 of 6 Old 03-10-2015, 02:50 PM
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Yea was my o2 sensor. But after i replaced it. Check engine light was still on went to orileys they hooked it to a machine an reset my compm an works fine geting average 15.5 mpgs witch is way better then 6-7 mpg. Of theres anything else i can do to it ro fet better mpgs let me kno. Ima be traveling in er alot.
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