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Thread: BF XR6T dying in the arse???

  1. #1
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    BF XR6T dying in the arse???

    hey all, i have a mates 07 BF xr6t Auto that wants some work done but before i do anything i would like to work out an issue its having so im hoping that some1 on here has had the same issue.

    ok soo it accelerates absolutely fine through 1st gear then up until around high mid-high rpm in 2nd or 3rd then it just stutters and wont make anymore power, then he'll back of to idle (stopped) and it idles rough, then he'll accelerate again it'll be sluggish and hesitant then all of a sudden it kicks back in and accelerates fine up until high mid-high rpm.

    at first i thought it may have been the fuel pump on its way out so we replaced it with a walbro 255 today (no change) as he re-gapped plugs 1 month ago and done top coils 5 months ago.

    any idea's fellas?

  2. #2
    any codes present sounds like possible overboost issues

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    no codes in ECU at all, ive data logged it and ive noticed the inj PW stays on 24.3ms during the stutter, manifold pressure is 155kpa but desired boost is 30kpa so i would assume its overboosting by 25kpa? then it also does it again stays on 24.2 ms inj PW, 154 kpa manifold pressure, desired boost 31 kpa

  4. #4
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    Valve springs
    04 Velocity MKII M6 & 06 BF F6 555 ZF6

  5. #5
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    I was thinking that for a while but it is a completely stock BF with 170,000km from memory, and after it hesitates under acceleration it will do it at idle too, if it were valve springs it shouldn't be running like shit at idle then come good I would have thought

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    Unless the valves are floating and the lifters are getting pump up, holding the valve open a little at idle till it bleeds back out? (I've never come across valve float or lifter pump up before so I'm not 100% sure on diagnosis other then bench pressure test them)

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    Quote Originally Posted by Bignatesmith View Post
    Unless the valves are floating and the lifters are getting pump up, holding the valve open a little at idle till it bleeds back out? (I've never come across valve float or lifter pump up before so I'm not 100% sure on diagnosis other then bench pressure test them)
    Exactly.
    04 Velocity MKII M6 & 06 BF F6 555 ZF6

  8. #8
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    Could it be floating because of the overboost? Or does desired boost at 30kpa not necessarily mean that's that that's the boost the computer is commanding?

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    Sounds like the ba I have that is hitting over boost due to messed up wastegate, we upped the desired boost so it wouldn't hit the over boost thresh hold, not the right way to fix it but it worked.

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    Hmm Righto, so just to clarify...if boost desired is less than (manifold pressure minus 100kpa)
    Is it over boosting?

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    If manifold pressure is under/over desired boost plus or minus over/under boost threshold. It will cut spark from my understanding.
    Last edited by will15; 05-08-2016 at 09:20 PM.

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    thanks will, ill have to check it out

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    Quote Originally Posted by will15 View Post
    If manifold pressure is under/over desired boost plus or minus over/under boost threshold. It will cut spark from my understanding.
    It won't cut spark once manifold pressure is reduced (ie when back at idle) The running rough up top then rough idle are classic symptoms of valve springs in these Engines.
    04 Velocity MKII M6 & 06 BF F6 555 ZF6

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    Yeah cutting spark would be a stupid way to reduce torque in an overboost situation, especially when you have DBW :-)

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    cheers everyone, you've been a great help..... i hvant seen the car since and i dont know when i will but ill let you guys know how it goes when and if he ever wants to pull the cover and test the springs

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    Does any know what boost cut will implement then, fuel,spark,dbw?, how does valve float make an engine run rough when it comes back idle?

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    the lifters pump up due to the float and once pumped up stop the valves from seating until they bleed down
    --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
    Thanks for your help
    Mark H.

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    Yeah that would do it, I have been doing a lot of research on this problem and lots of people are coming across this. Some are saying the symptoms are the same for boost cut and valve float. The boost cut problem I had were the same.

  19. #19
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    Completely different results for those two situations champ
    FG F6 400+RWKW .....10.9 @ 132mph.... FIRST 10sec F6 in SA ( sold )
    DYNO DYNAMICS 1200hp ...... Tuning weapon..... ( sold )
    OFFICIAL JONNY TIG INDUSTRIES SUPPLIER ..... Biggest and lightest intercoolers for B and F falcons
    SUBARU BRZ ......AVO TURBO KIT coming......soon
    VF R8 CLUBSPORT SV...... 340FWKW.....ASE BIG SINGLE KIT .....one day

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    Can you discribe what boost cut feels like and what actions the ecu implements?.