Tacoma: DTC:PO172... Fuel trim?

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Thread: Tacoma: DTC:PO172... Fuel trim?

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    Default DTC:PO172... Fuel trim?

    Hi Guys !
    Glad your here. I'm new to this forum. I'm working on my nieces, (no $$), 2k Tacoma 4x4 3.4 5spd w/California Emissions. The MIL (malfunction Indicator Light a.ka. CE light) comes on and OBD2 scan shows PO172. Symptons include a bog when accelerating (sure wish it was a good 'ole carb Acc pump ;-) and a slight surge under light load.

    Tested / Tried :
    No intake or exhaust leaks
    grounds all good
    Fuel Pressure / Filter is new
    Has new NGKs
    A/F sensor is brand new OEM
    Tested MAF ( resistance and voltage OK but Alldata does not give voltage specs other than it should vary when air is blown through it. Anybody know values 4 MAF voltage ?

    Any Ideas or experiences ???




    I have a small shop in Western Mass and have specialized in Asian vehicles (mainly Subies) for 25 years.


    BEWARE !!!
    Air/Fuel Sensor that looks EXACTLY like a common heated O2 Sensor only it costs 4 to 6 times as much. Trust me , if O2 sensor is installed where A/F sensor is it will run like a POS !!

    Thanks for any help.
    Jon

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    Quote Originally Posted by Knuckle Buster
    Hi Guys !
    Glad your here. I'm new to this forum. I'm working on my nieces, (no $$), 2k Tacoma 4x4 3.4 5spd w/California Emissions. The MIL (malfunction Indicator Light a.ka. CE light) comes on and OBD2 scan shows PO172. Symptons include a bog when accelerating (sure wish it was a good 'ole carb Acc pump ;-) and a slight surge under light load.

    Tested / Tried :
    No intake or exhaust leaks
    grounds all good
    Fuel Pressure / Filter is new
    Has new NGKs
    A/F sensor is brand new OEM
    Tested MAF ( resistance and voltage OK but Alldata does not give voltage specs other than it should vary when air is blown through it. Anybody know values 4 MAF voltage ?

    Any Ideas or experiences ???




    I have a small shop in Western Mass and have specialized in Asian vehicles (mainly Subies) for 25 years.


    BEWARE !!!
    Air/Fuel Sensor that looks EXACTLY like a common heated O2 Sensor only it costs 4 to 6 times as much. Trust me , if O2 sensor is installed where A/F sensor is it will run like a POS !!

    Thanks for any help.
    Jon
    P0172 - System too Rich (Fuel Trim) (Except
    California Spec.)

     Injector leak, blockage
     Mass air flow meter
     Engine coolant temp. sensor
     Ignition system
     Fuel pressure
     Gas leakage on exhaust system
     Open or short in heated oxygen sensor (bank 1 sensor 1)
    circuit
     Heated oxygen sensor (bank 1 sensor 1)
     ECM
    Attached Files Attached Files
    ~Glenn
    Yes I am a pirate!


    "To err is human. To arrr is pirate."

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    Thread Starter

    Unhappy Code PO172

    Thanks for the speedy reply nhparrot !!


    The files you attached are for Federal emmissions , this is a California spec vehicle ,although some specs/test are the same , I'm not sure the Federal uses an Air/Fuel sensor. There certainly isn't much discussion of A/F sensor equipped cars here or on other forums.

    I did the Engine coolant temp. sensor tests

    Fuel Pressure is on the money

    The o2 sensor tests fine.

    Not much to test in the ignition (new plugs and no misfire codes)

    Not sure what they mean by "Gas leakage ON exhaust system"

    I did both tests on the MAF meter although, like I stated, My ALLDATA info is vague as far a voltage fluctuation test ( no specs )

    Injector leak, blockage ? How in the world can this be tested ? I can't visualize a way to check spray patterns onboard.
    If there was a way to bench test, just getting the out is a nightmare. Also,wouldn't a leak or blockage cause missfire and ragged running ? I may do injector clean if I can adapt my setup. Owner ran a double shot of Techron in fuel to no avail.

    Other than the bog/hesitation like a "Q-jet" with no accelerator pump , the truck runs great !!
    B.T.W. , only has 52K on the clock

    Any help greatly appreciated !!

    Jon
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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ID:	4472  
    Last edited by Knuckle Buster; 08-26-2004 at 10:30 PM. Reason: Attachment failed to upload

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    some more help
    Attached Files Attached Files
    ~Glenn
    Yes I am a pirate!


    "To err is human. To arrr is pirate."

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    Quote Originally Posted by nhparrot
    some more help
    GEEZZZ GLENN!!!

    Sooo MUCH info from one guy! What ARE YOU man... a Toyota "ENGINEER"?!

    No... I know... you're a... "Pirate Looking At 40"... or a... "Son Of A Son Of A Sailor"... or maybe you're just spending a lot of time in... "Margarettaville". Sorry... I just couldn't help myself. I "pose" you can tell... I'm a "Buffet-Nut/Parrothead" too!

    Either way man... you're a "wealth" of knowledge there dude!

    Dave

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    Wink

    ...man, now i feel like a cheeseburger in paradise

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    Default

    First couple of things I would do is

    #1 Have battery checked with VAT45 or equvilant
    #2 Check fuel pressure @ Idle
    #3 check fuel pressure while cruising
    #4 Check fuel pressure under a load
    #5 Remove after market air filter (IF EQUIPPED)
    #6 Clean Maf sensor <-----common problemI have usually found DEBRIS inside the sensor itself.
    #7 Find out what the "LONG TERM FUEL TRIM" is = (What % it is running?)
    I am still researching, will post more later.

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    Quote Originally Posted by mustang67408
    #6 Clean Maf sensor <-----common problem
    Ditto that. My wifes RX300 was recently squawking P0171 (lean vs. rich) and after cleaning the MAF and throttle body, the problem went away and has not returned. It is worth a try since it requires no new parts.

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    Default maf dirty

    Hey there.
    Try just looking at the wires inside the maf. They are probably covered in dirt. It usuallt sets a p0171 systen too lean but i have seen about 10 or so that set the system too rich code. Take your scan tool and set it up to look at short fuel trim and long fuel trim remember the numbers then clean the maf with either alcohol or brake clean then reset the mil and look at the fuel trim again. You should see the short fuel trim go opposite of the long fuel trim. then then long f/t will start changing as the computer learns the new settings and the short should start flucuating between -3% and +3% all will be well again. After you get that fixed up look at the air filter and the airbox to make sure no dirt is getting aroung the filter (that is why the maf is getting dirty) hope this helps. And by the way , the voltage never seems to out of spec. I cant tell you why though.

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    Default

    See if your scan tool will read the MAF sensor gm/sec. At idle you should see around 4-5gm/sec, and @ 2500rpm it should be 13-14gm/sec.

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