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Thread: Sanity Check for P0171

  1. #1
    Comp Engineering Student Riot_Polizei's Avatar

    2002 Mazda Protege5

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    Sanity Check for P0171

    Hello guys, as stated, this is a bit of a sanity check.

    Should I expect P0171 (system too lean) to come on more often if I have a cold air intake installed on the car?

    If so, I probably shouldn't be too concerned, but am still investigating other causes.
    Last edited by Riot_Polizei; 04-03-2019 at 06:05 PM.
    2002 Mazda Protege5
    ■ Sunburst Yellow ■ Black Rear Valence ■ Injen Cold Air Intake ■ Racing Beat Catback Exhaust ■ Moog Front Endlinks
    ■ Megan Racing Rear Strut Tower Bar ■ Racing Beat Rear Sway Bar ■ Mazda6 Front Big Brakes ■ Foglight Deletes
    ■ OBX 4-1 Headers ■ MP3 ECU ■ VTCS-less Intake Manifold ■ Mishimoto Aluminum Racing Radiator + Fan Shroud
    ■ AWR Trailing Arms


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  2. #2
    ......................... i12drivemyMP5's Avatar
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    I have an intake from vendor on here, 505zoom.......filter box sits over the hole into the fender well so it breathes from same place. I occasionally get this lean code, mostly in winter when air is colder/denser. There are no air leaks anywhere. My MAF is clean, washable dry-flo filter - no oiling. If I wait until it is warm/humid (like it is here most of time) then the code won't happen and passing inspection is no problem. Won't pop a code all summer/fall.

    This is my intake setup..................

    Last edited by i12drivemyMP5; 04-04-2019 at 12:28 PM.

  3. #3
    Comp Engineering Student Riot_Polizei's Avatar

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    Nice n'clean...

    Do you have a way to measure fuel trims, perchance? I want to compare, if possible
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  4. #4
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    lolmsp

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    i'll add my experience here. Bought MSP in 2009. That CEL comes and goes even before and after my engine swap. During engine swap, car got all new seals and vacuum hoses and what not. CEL lasts for about a day or two. Maybe my car is just psycho like i12drivemyMP5's P5.
    03 MSP, 03 P5

  5. #5
    The Diagram Dude pcb's Avatar

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    I'm thinking weak fuel pump and dirty fuel filter.

    The Diagram Dude

  6. #6
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    lolmsp

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    no! you get that out of here right now.
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  7. #7
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    protege5

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    I don't know what the air flow rate is with the cold air intake vs. the OEM intake, but I would have to imagine it's a pretty significant difference. especially if you have exhaust, headers, etc. to push even more air flow through the motor.

    The stock fuel injectors are tuned and set up for the stock intake. If you're doubling the amount of airflow, it may be just borderline between where it kicks a code or does not kick a code. The stock ECU/Injectors is engineered and designed to work. There is a certain amount of headroom for safety, but once you start doing a certain amount of upgrades, it can bypass what the factory curves are able to support. Cold air is more dense, so would be more air to the fuel mix (leaner). This doesn't mean you're still not running lean when it's warmer. The ECU has a threshold of when it kicks a code. IT may just be that when it's warm, it's inside this threshold (barely) but the colder denser air is enough to put it over the threshold and kick the light. The only way to compensate would be to go with a little larger injector and/or fuel management system.

    But first, I would make sure your injectors are clean, fuel pressure is per spec, etc. Go through and do a full tune up, make sure the MAF/MAS is clean, etc. I definitely would not recommend running it hard or much with it being lean or bad things can happen.

  8. #8
    Comp Engineering Student Riot_Polizei's Avatar

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    I got some readings regarding my fuel trim, and it's not looking good. I only collected data while driving around, and not stationary.

    STFT was bouncing all around, but only rose above 8% at very low engine speeds (around 1.5krpms and lower, I believe). LTFT stayed at 25% (overwhelmingly lean trend). STFT had "normal" readings above 1.5-2kRPM readings, which ultimately points at a vacuum leak of some kind, and not necessarily a fueling issue.

    At least, it's been narrowed down, but damn I msy habe to rip open my IM again...

    (Note: will analyze this at stamdstill later)
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  9. #9
    The Diagram Dude pcb's Avatar

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    Quote Originally Posted by Riot_Polizei View Post

    STFT was bouncing all around, but only rose above 8% at very low engine speeds (around 1.5krpms and lower, I believe). LTFT stayed at 25% (overwhelmingly lean trend). STFT had "normal" readings above 1.5-2kRPM readings, which ultimately points at a vacuum leak of some kind, and not necessarily a fueling issue.
    I could see a lack of fuel pressure causing those symptoms.
    At lower rpms, the engine is using less gas so the fuel pump can keep up but on average over time, your LTFT will be reduced.

    A fuel pressure test could be done but it's a bit of a chore.

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  10. #10
    The Diagram Dude pcb's Avatar

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    Your pump may be able to put out ~30-36 PSI but perhaps not able to put out the 64-92 PSI when the ECU calls for it.

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  11. #11
    The Diagram Dude pcb's Avatar

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    You could also check to see if your fuel pump is running almost nonstop, suggesting that it's having a hard time building pressure.
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  12. #12
    Comp Engineering Student Riot_Polizei's Avatar

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    I just popped the hood and heard it myself--a small, unmistakeable hiss from around my IM.

    My VICS actuator was easily pushed open and seemed to hold no vacuum so now I know where to start digging
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  13. #13
    The Diagram Dude pcb's Avatar

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    OK.
    I digress.
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  14. #14
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    i got an empty slot for one last gauge. maybe it should be a fuel pressure gauge.
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  15. #15
    Comp Engineering Student Riot_Polizei's Avatar

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    Found and fixed the culprit!

    When installing my IM, I did not properly torque down one/two particular bolts near the middle of the head. This, in turn, caused the IM gasket to collapse at the top and allow lots of air to flow in. Damn.

    A new gasket was dropped in, everything was torqued to spec according to the manual. No vacuum lines were damaged.

    Man, I gotta do things right the first time, or else I'll have a non-stop Mazda-induced aneurysm.
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