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system too lean bank 1, system too lean bank 2

- Ford-F150

Forum Post
07/12/09 09:35

system too lean bank 1, system too lean bank 2

I have a 2000 f-150 5.4, 2 wheel drive. I get error codes 171 and 174, system too lean bank 1, system too lean bank 2, after about 10 mins. of driving. Sometimes one, sometimes the other, sometimes both. I've checked for vacuum leaks but found none. Any suggestions would be appreciated.


Archived Replies

This post has a total of 27 replies. The most recent 25 are shown below, you can view the complete archive here: system too lean bank 1, system too lean bank 2 archive. Your feedback, comments, opinions and questions are welcome and encouraged.

This forum post has messages dated from 07/12/09 through 11/10/12, please be sure to read all the messages. If you feel it is old or outdated, please follow up with a question or comment and someone may be able to update it, or reply with newer information if you have it.

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Goran Borsi

i had the same problem i had to replace all 4 of the oxygen sensors... if that does not do it.. then you probably have a leaking vac. hose... try that... and it doesn't hurt to put Seafoam in your tank...

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B&E Auto

try the pcv hose all ford truck motors have it. probably under the throttle body. the hose will probably be squishy and there will be a hole in the elbow
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Rick M

96 mustang gt x eng put used eng in it, now sets 171 and 174. as soon as it goes in closed loop, short term ft max out 33.3%. fuel psi good, new ford mass air, new dorman intake. cant find a vacuum leak. take oil cap off, changes eng rpm. please help
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it could be the massive air flow sensor
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I have a 2001 f150 4.2 v6 and obg said bank 1 and bank 2 too lean, I've been asking around, and a few people said to check o2 sensior and or mass air flow sensior(maf), haven't done it yet also do you think a hole in the exhuast will efect bank 1 and 2.... Also his truck has been rolled it's a prerunner so sensiors may be dirty right help please
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i have a explorer 2000. its 4wd 4.0 liter v6 sohc. i get codes po171 po174 bank1 and bank2 lean. i have replaced fuel filter, cleaned MAF sensor, checked for vaccum leaks by carefully spraying some wd-40 around suspected areas to see if engine revs at all. no apparent vaccum leaks. i have not checked my fuel pressure at the injectors which i plan to do next along with taking apart my throttle body to see if things inside are gunked up. does anyone have any other idea for me to try if so please let me know i really didnt see this as being a hard fix but has been bugging me for about a week now. how often is this problem caused by a fuel pump going out i feel skeptical that this is the problem although one time about 3 days ago at every red light it stalled but this only happened one time after going about 30 miles. please help if u have any more ideas thank you.
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also i forgot to mention, on a 2000 ford 4.o liter sohc where the heck is the pcv valce i cannot locate it i know almost all fords have one but mine is seemingly invisible. my truck would be really really great condition if i can get this problem fixed so i would appreciate any input.

po171 po174 also i only replaced the two upstream o2 sensors should i have replaced the downstream (catalytic monitor) sensor in this case for these codes???

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The banks on your engine are ran by your o2 sensors but there are also a couple of other sensors that could throw them out of range. check fuel pressure regulators also
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On my 1998 Ford F150 i replaced the fuel filter, air filter and i cleaned the MAF (Mass

Air Flow Sensor) with a can of Mass Air Flow Sensor Cleaner. I then disconnected the NEG battery cable for about 30 minutes to reset the error code. That fixed the problem for me.

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I have a 1998 F150 5.4 - the failure on mine was a vacuum leak at the throttle body end of the pcv line. Here is a link to the picture - the part on mine that was leaking is circled in red

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I have a 1998 F150 5.4 - the failure on mine was a vacuum leak at the throttle body end of the pcv line. Here is a link to the picture - the part on mine that was leaking is circled in red
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i am working in afghanistan i am mecanic
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I have a 98 ford Mustang. Had a used engine put in 3 years ago. just recently i has ro get a jump free getting gas and I also had a oil change a few days go and thats when the serious problems started. I now have the same codes 171 and 174 after driving for about 45 minutes on th highway then taking the streets I have been experiencing a very rough idle at lights or any stops and Its also misfiring and feels like it's going to shut off n the check engine light comes on. I have been to 2 mechanics they both said I needed a tune up and a battery that DID NOT FIX THE PROBLEM. NOW 220 dollars later I still have the same problem. Went to Aamco and they told me I need a compression test and some other test to figure out exactly what the problem is with those two codes because my car is running lean. Should I get the two tests done???I do not want to keep wasting money that I don have. PLEASE HELP!!!!!!
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Sorry about the typos used my phone to post that. I hope someone can decipher what I wrote and get back to me thank you
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Mark DeMonaco

I had this same problem on my 2001 Ford F150 4.2 v6. The first thing I would recommend is to change the plenum gaskets and isolator bolts. Seems to be a common problem for the Fords. Unfortunately this was the last thing I tried. Could've saved a ton of money had I done this first.
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I have a 98 ford mustang v6 3.5 liter and recently i drove to houston and back so bout 400 miles and i just got this car used. the check engine light has come on and the car is having trouble going after about 30 mph it doesn't wanna go we checked the computer and it said that bank 1 and bank2 o2 sensors were sensing not enough fuel. It said too lean... I don'[t understand this we put all new spark plugs, air filter, changed oil, cleaned out radiator and block, and checked for vaccum leaks but still nothing please HELP!!!
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sorry it's a 3.8 liter you guys ooops.
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I rubbed big mac sauce on my mass air flow sensor. It fixed the 171 and 174 codes.
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charles marshall

hi i have a 2001 f150 with the 4.6 its saying running lean in bank one and its leaking antifreeze frome somewhere i cant see but i have recently replaced the pcv valve and head gaskets and intake gaskets and exhaust manifold and egr return pipe from exhaust and yesterday it ran fine after putting the new pcv in but today on my way to drill its started running like and leaking any thoughts on what it is im really tired of tearing it apart and putting it back together and not getting fixed although i do everything by the book and i know everything is right
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Just some dude

Reply #13 is acurate. Wow, so of you other tards must enjoy wasting peoples time and money. Why do you post bull? If you dont know, dont act like ya do. So anyway, thanx RED, the vac leak explains the rough idle and the trouble codes.
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Big mac sauce?? You are f-ing retards... I hope your not fixing cars for a living or there will be a lot of assed out people. Don't listen to Sancho up there.
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New York, Sticks
Thank author of this post/comment"bank 1 and bank 2 are lean"

My 2000 Ford Explorers engine light is on. As weather gets colder my truck starts worse. Almost like it dogs out. Almost stalls sometimes. Sometimes does. As soon as my truck gets whatever through it's system it runs fine for rest of time. But after not driving for 8 hours it'll do it all over again. I've replaced plugs. Egr valve. Checked mass air flow intake. When I unplugged maf it would stop dogging out. Any ideas.
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Thank author of this post/comment"Thanks B & E Auto"

Thank you Comment #4 B & E Auto. I was getting the code PO171 on my F150 and system too lean bank 1 was very vague. I checked the little elbow hose like you recommended and sure enough there was a hole. much cheaper fix than I imagined it would be.
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fresno CA
Thank author of this post/comment"isolator bolts (plenum) bank 1 and bank 2 too lean"

if u chacked for vaccum leaks, pvc valve, etc and cleaned the MAF Sensor and still havent got it fixed. replace the isolator bolts if it has the plastic intake(plenum) and the seals .don't replace the lower metal gasket atached to the engine between th aluminium intake. this will fix both lean codes. replaced all this on my 2001 f150 v6 4.2L extra cab. a month ago and everything is fine now. if you dont have a obd scan tool to erase the code just disconnect your battery for 10 minutes or so. then connect it again. it should not show the engine ligh on anymore.
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    Archived Replies

    This post has a total of 27 replies. The most recent 25 were shown above, you can view the complete archive here: system too lean bank 1, system too lean bank 2 archive. Your feedback, comments, opinions and questions are welcome and encouraged.

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    Ford F150 'system too lean bank 1, system too lean bank 2'