she stumbles past 4k... is this limp mode

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Thread: she stumbles past 4k... is this limp mode

  1. #1

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    she stumbles past 4k... is this limp mode

    she was low on fuel.. drove her to the gas station without boosting..
    noticed that she wont go past 4k without stumbling...
    after refueling... she took a while to start and thick black smoke was spewing out the exhaust but she started after multiple cranks..
    same deal after driving her... wont go past 4k
    going to remove the negative on the battery overnight and see what that does... any ideas on what this could be..

    one thing to note is that i put on a new rad.. tstat and battery prior to this.. deleted the windshield washer tank...nothing was disturbed during this install
    Last edited by amp; 04-16-2019 at 05:56 AM.

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    What is your set up? Stock twins? Check your VSV for the 2nd turbo.

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    97 tt.. single turbo sx366.. 1400cc.. 14mm fuel rail
    no cel btw and its only hot start when she require multiple cranks..
    she does turn over but have to pump the throttle and push gas to have her stay on...
    Last edited by amp; 04-16-2019 at 05:56 AM.

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    update... fuel pressure is @ constant 42psi.. it stumbles past 4-4500 at load and at idle also
    Last edited by amp; 05-09-2019 at 10:39 AM.

  7. #5
    Very Senior Member Silver Supra's Avatar
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    No - it is not limp mode. You will understand if it ever goes into limp mode!!
    There could be a number of causes - it could be a fuel issue - something as simple as a filter.
    Start with the simple stuff - although there are some serious problems that start this way. Jared at Speed for Sale could describe what we found when I had similar thing happen.... Ended up with a different head and some more stuff!!
    Last edited by Silver Supra; 04-14-2019 at 09:31 PM.
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    Quote Originally Posted by amp View Post
    update... fuel pressure is @ constant 42psi.. it stumbles past 4-4500 at idle also
    When you say constant I'm not sure how you mean that. 42 is good base fuel pressure but it should go up 1 to 1 with boost.
    Nick 95 6sp
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    Quote Originally Posted by Silver Supra View Post
    ... it could be a fuel issue - something as simple as a filter.
    Start with the simple stuff - although there are some serious problems that start this way....
    going to change fuel filter next... not looking forward to that
    22 year old car... yeah i knew what i was getting into.. just hoping its not too serious


    Quote Originally Posted by Nick 95 6sp View Post
    When you say constant I'm not sure how you mean that. 42 is good base fuel pressure but it should go up 1 to 1 with boost.
    was referring to idle not under load... thinking perhaps it would indicate a clogged system or bad pump if low...
    dont have a way to check or log pressure while boosting atm...

    changed the plugs last night... gapped .25 ngk bkr7e
    took her for a drive in the morning and same deal... pops and bogs past 4500
    old plugs are black.. would indicate rich condition
    no cracks on coils|boots...
    Last edited by amp; 05-09-2019 at 10:41 AM.

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    Speaking of fuel filter, is oem still the way to go for bpu ?

  11. #9
    handy with the steel CDSaints's Avatar
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    was referring to idle not under load... thinking perhaps it would indicate a clogged system or bad pump if low...
    dont have a way to check or log pressure while boosting atm...




    This would be #1 on my list of things to check. What kind of fuel/ignition management are you running? Anything that can produce some logs would be helpful. Regardless, if you don't have a way to monitor, or at least log the fuel pressure then get one.


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  12. #10

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    changed the fuel filter and spark plugs... same deal
    backfires when she hits 5 grand from idle.. as far as she will go...

    ive been told to swap IAC if not at spec..

    could a boost leak cause this... will order a boost leak tester next...
    Last edited by amp; 05-09-2019 at 10:45 AM.

  13. #11
    Quote Originally Posted by amp View Post
    changed the fuel filter and spark plugs... same deal
    backfires when she hits 5 grand from idle.. as far as she will go...

    ive been told to swap IAC if not at spec..

    could a boost leak cause this... will order a boost leak tester next...
    I had this exact problem on my Evo. Turned out to be a bad IACV AND Coils were on their way out..
    You need to find a way to monitor fuel pressure, injector duty cycle, & afr/lambda while under boost.
    Otherwise you'll just need to throw parts at it. In which case i'd start by swapping out IACV, the coils, and/or your fuel pump.
    But yeh that boost leak test isn't a bad idea either.

    Have you noticed any new noises coming from your gas tank, or injector ticking?
    Pull the pump and check the coloring on the housing.
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  14. #12
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    Quote Originally Posted by amp View Post
    backfires when she hits 5 grand from idle.. as far as she will go...
    .
    The factory has a limiter at idle at 5k RPMS. That is completely normal.

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    Quote Originally Posted by amp View Post
    changed the fuel filter and spark plugs... same deal
    backfires when she hits 5 grand from idle.. as far as she will go...

    ive been told to swap IAC if not at spec..

    could a boost leak cause this... will order a boost leak tester next...
    You're running 1400cc injectors on a stock ECU?!?
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    Quote Originally Posted by Brotato View Post
    I had this exact problem on my Evo. Turned out to be a bad IACV AND Coils were on their way out..
    You need to find a way to monitor fuel pressure, injector duty cycle, & afr/lambda while under boost.
    Otherwise you'll just need to throw parts at it. In which case i'd start by swapping out IACV, the coils, and/or your fuel pump.
    But yeh that boost leak test isn't a bad idea either.

    Have you noticed any new noises coming from your gas tank, or injector ticking?
    Pull the pump and check the coloring on the housing.
    doesnt appear to be IAC... measures the same resistance as a known working one..
    goin to check for boost leak first before grabbin new coils and the dang $400 IAC...

    Quote Originally Posted by cwtt View Post
    The factory has a limiter at idle at 5k RPMS. That is completely normal.
    Quote Originally Posted by Wreckless View Post
    You're running 1400cc injectors on a stock ECU?!?
    shes on AEMV2..
    Last edited by amp; 05-10-2019 at 10:31 PM.

  17. #15

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    Sounds like it could something as easy as plugs. Turbo cars tend to foul plugs relatively quick, or the gap could have gotten messed up. Try just a simple tune-up. I have had cars stumble as soon as they hit boost, or once the timing advances the plugs cant keep up. Cheap place to start and youll have to do it eventually anyways.

  18. #16
    Quote Originally Posted by CR820 View Post
    Sounds like it could something as easy as plugs. Turbo cars tend to foul plugs relatively quick, or the gap could have gotten messed up. Try just a simple tune-up. I have had cars stumble as soon as they hit boost, or once the timing advances the plugs cant keep up. Cheap place to start and youll have to do it eventually anyways.
    OP mentioned he changed the plugs already. I wonder if he took pics of each/read the plugs?

  19. #17
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    Quote Originally Posted by amp View Post


    shes on AEMV2..
    Are you getting a speed signal in the log? You could be stuck on your 2step. Set the 2step limiter to 8000rpms and try again.

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    Try re-flashing the MAP back onto the ECU. Also are you Auto or Manual?

  21. #19

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    Quote Originally Posted by Brotato View Post
    OP mentioned he changed the plugs already. I wonder if he took pics of each/read the plugs?
    800px_COLOURBOX24279991.jpg
    new at top... old at bottom.. same as the rest...

    Quote Originally Posted by cwtt View Post
    Are you getting a speed signal in the log? You could be stuck on your 2step. Set the 2step limiter to 8000rpms and try again.
    will be downloading the software after the boost leakdown test and see if i can make heads or tails with it...
    just enough to read values when she stumbles..

    Quote Originally Posted by NotyMKIV View Post
    Try re-flashing the MAP back onto the ECU. Also are you Auto or Manual?
    dont have the tuned map to reflash her with unfortunately..
    v160 swap...


    .. battery was disconnected for a few weeks before this happened..
    any possibility that settings was lost and im on some base map thats restricting me..
    Last edited by amp; 05-15-2019 at 10:45 PM.

  22. #20
    Quote Originally Posted by amp View Post
    .. battery was disconnected for a few weeks before this happened..
    any possibility that settings was lost and im on some base map thats restricting me..
    the ecu should have a small on-board battery to retain the state of any flash/ram based memory.

  23. #21

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    Quote Originally Posted by amp View Post
    800px_COLOURBOX24279991.jpg
    new at top... old at bottom.. same as the rest...



    will be downloading the software after the boost leakdown test and see if i can make heads or tails with it...
    just enough to read values when she stumbles..


    dont have the tuned map to reflash her with unfortunately..
    v160 swap...


    .. battery was disconnected for a few weeks before this happened..
    any possibility that settings was lost and im on some base map thats restricting me..
    Holy crap those plugs are toast. Depending on how long of an interval you did in between changes, those look like you're running REAL rich. Do you have an AFR gauge, and if so what number is it reading under WOT?
    EFI has its own system that will retain data when the battery is DCed.

  24. #22

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    so finally got to do the boost leak test..
    she cant hold more than 3lbs of pressure..
    the leak seems to be coming from underneath the fuel rail..
    my guess is that its the intake mani gasket ... but arent these metal..
    have had similar hot start up issues and stumbling with my old honda passport with a failed intake mani gasket..
    should have remembered this..
    i initially thought the leak was coming from an old line that ran to the bov but they tested ok..
    line to fpr is ok too... anything else in that area where it could leak that yall can think of before i tear her down..

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