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Thread: Trouble Starting and P0171 ECM CEL

  1. #1
    Living the wagon life...

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    Trouble Starting and P0171 ECM CEL

    So Ive been spending a lot of time researching the CEL P0171 aaaaaaaaand Im really stumped. But let me back up

    A few weeks back, my P5 started having issues starting. Its gotten to the point where it takes roughly 2-3 times turning the motor over letting it rotate 4-5 times each cycle to get it to start. I can leave it to crank and it takes roughly 10-15 turns before it finally catches... And no matter which way I do it, the motor the starts weak then stumbles up to normal operation.

    Thru my research, Ive replaced the upstream O2 sensor, the cam angle sensor and the crank angle sensor. Since I got the car almost 2 years back, I changed out damn near everything on my fuel system due to the pinging issues our cars experience in the heat. This included brand new parts for everything listed... Bosch fuel pump, OE 1.8 liter coilpacks, NGK plug wires, OE long tip spark plugs, OE fuel sending unit, OE fuel pressure regulator, OE injectors and OE fuel pulsation damper, Mishimoto aluminum radiator, SAMCO hoses and a Mishimoto cooler thermostat (I live in Vegas where its a billion degrees in summer). Ive cleaned the MAF numerous times, I have an AEM short ram intake with K&N conical filter (gets cleaned every few months with K&N cleaning kit) so there are no cracks in my intake piping (ive checked all of the couplers as well). Ive checked all the vacuum lines in the engine bay (outside of the 1 way check valve inbetween the runners of the intake manifold)... havent found a single cracked line. Im about to say screw it and replace ALL of the vacuum lines just so I know that issue is ruled out.

    The car is currently having issues with bogging during acceleration up until around 3500 rpms (this started before the CEL came on). Last Tuesday while driving around, my CEL came on. I pulled the code with an OBD2 reader and started researching, plus replacing sensors that have been listen in regards to the CEL. I cleared the code a few days back, and the CEL came back on today driving over to Lowes.

    So yeah, input please... This code seems to be REALLY vague and its literally like you just have to throw parts at the car until it fixes the problem.
    Last edited by dorkidori_s13; 02-06-2018 at 11:15 AM.


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  2. #2
    The Diagram Dude pcb's Avatar

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    Try putting your key to run position and waiting about ten seconds or more before cranking over the engine.

    Some guys fuel rails appear to hold pressure for more than a week... Other people seem to lose pressure in about fifteen minutes. There doesn't appear to be a fuel check valve. I'm pretty sure the pressure is held by the fuel pump impeller itself.

    You didn't mention replacing your PRC solenoid valve... If that is leaking your fuel pressure regulator won't work properly.

    One guy just recently had hard starting and it was due to dirt on his ECT sensor. He cleaned it and the issue stopped.

    The ECU needs to know the engine temperature to do a hot or cold start.
    If it is a hot start, the fuel pressure needs to be higher.

    Make sure your IAT sensor is clean as well.

    If you can get a fuel pressure tester, it will help you trace your fuel system to isolate a fuel related problem.
    It's listed as a Specialty Shop Tool but a generic version would probably work and it might be available as a loan a tool.
    The testing procedure is outlined in the service manual.
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  3. #3
    The Diagram Dude pcb's Avatar

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    When you say you replaced your fuel sending unit you mean this part correct??



    There is a fuel filter inside the housing that can get clogged.
    Last edited by pcb; 02-05-2018 at 05:16 AM.
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  4. #4
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    Quote Originally Posted by pcb View Post
    Try putting your key to run position and waiting about ten seconds or more before cranking over the engine.
    already did this, doesnt change a thing


    Some guys fuel rails appear to hold pressure for more than a week... Other people seem to lose pressure in about fifteen minutes. There doesn't appear to be a fuel check valve. I'm pretty sure the pressure is held by the fuel pump impeller itself.
    theres a small check valve near the fuel rail, im trying to figure out a replacement for it seeing as i cant find a part listing (big surprise for our cars)


    You didn't mention replacing your PRC solenoid valve... If that is leaking your fuel pressure regulator won't work properly.
    i may be purchasing a new one soon, but this only really effects the pressure inside the tank (from what ive read). the PRC is supposed to relieve excess pressure thats built up due to heat.


    One guy just recently had hard starting and it was due to dirt on his ECT sensor. He cleaned it and the issue stopped.
    havent checked this, but my coolant system looked clean as a whistle for having over 200k miles on it when i swapped out the thermostat and radiator hoses.


    The ECU needs to know the engine temperature to do a hot or cold start. If it is a hot start, the fuel pressure needs to be higher.
    middle of winter, not a problem at the moment. wasnt an issue either during the summer after i changed radiator/thermostat


    Make sure your IAT sensor is clean as well.
    non issue as i clean it every time i clean the MAF, which is usually every 3 to 6 months. cleaned both on Saturday, problems still persist.


    If you can get a fuel pressure tester, it will help you trace your fuel system to isolate a fuel related problem. It's listed as a Specialty Shop Tool but a generic version would probably work and it might be available as a loan a tool. The testing procedure is outlined in the service manual.
    this is most likely going to be my next step... everything is boiling down to feeling like a bad pump at the moment. ive had numerous walbros go out in my S13s over the years and the symptoms feel very similar. probably just gonna go buy an adjustable fuel pressure regulator, a fuel rail and a walbro 255lph pump. even if its not the problem, at least ill be able to add a dash more fuel pressure to see if i can eliminate the pinging issue during the summer given i think the factory tune on my ECM is what causes the issue and it just needs a pinch more fuel pressure to eek out some more gas in those cylinders!


    Quote Originally Posted by pcb View Post
    When you say you replaced your fuel sending unit you mean this part correct??. There is a fuel filter inside the housing that can get clogged.
    yes, i replaced the ENTIRE sending unit with a brand new one from Rock Auto about a year or so back.
    Last edited by dorkidori_s13; 02-05-2018 at 06:32 PM.
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    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by dorkidori_s13 View Post
    i may be purchasing a new one soon, but this only really effects the pressure inside the tank (from what ive read). the PRC is supposed to relieve excess pressure thats built up due to heat.
    I think you're thinking that we're thinking about the purge control valve...
    That relates to fuel vapour pressure...

    I'm talking about the fuel pressure regulator solenoid valve. .

    That valve adjusts vacuum sent to the fuel pressure regulator to adjust fuel pressure up and down.
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    The Diagram Dude pcb's Avatar

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    you said you found a cracked vacuum line... that should be the first place to start. if the car still has trouble starting after taping up/replacing the line, you can rule that out.

    you didnt mention if the car has more trouble starting when hot or cold. or is it the same?

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    PO171 by definition means that the PCM is needing to add much more fuel than the amount it considers to be normal to achieve a decent AFR. If you were to check your fuel trims, they'd be in the high positives, (+20 give or take).

    As for probably causes, vacuum leak, low fuel pressure, faulty 02, etc.

    Maybe the pinging is from your SRI?
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  9. #9
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    Quote Originally Posted by GJ-Molestor View Post
    you said you found a cracked vacuum line...
    that was a typo boss...

    you didnt mention if the car has more trouble starting when hot or cold. or is it the same?
    both
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  10. #10
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    Quote Originally Posted by MrGiggles View Post
    As for probably causes, vacuum leak, low fuel pressure, faulty 02, etc.
    downstream replaced with delphi unit summer of last year. upstream replaced with delphi unit last friday (02-02-18)

    Maybe the pinging is from your SRI?
    i fail to see how a short ram intake would create a noise that mimics pinging.
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    Quote Originally Posted by dorkidori_s13 View Post
    downstream replaced with delphi unit summer of last year. upstream replaced with delphi unit last friday (02-02-18)



    i fail to see how a short ram intake would create a noise that mimics pinging.
    More from high IATs.
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    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by MrGiggles View Post
    Maybe the pinging is from your SRI?
    You might want to consider getting an intake that draws from the fender area behind the bumper.
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