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  1. #1
    b_dolla44's Avatar
    Join Date
    Apr 2008
    Noblesville, Indiana United States

    HELP!!!!! Low rpms. (7200-7600) with 2 rude/ Riva ECU ect...

    Im trying nto help my brother ( forum member j_dolla) with his engine issues and we need some help guys!

    For starters here is somem back ground info.

    he purchased a 2005 GTX limited from a friend last year for a fair price because it had a supercharger failure. The GTX had its orignal SC replaced around 100 hrs with a brand new 08 215SC.
    But the since then it had never been serviced (now at 490+ hours)

    Needless to say the SC lost a bearing and lodged itself between the PTO and flywheel causing it to lock up.

    We pulled the engine and replaced the front and rear oil pumps, PTO, SC etc.

    Took it out and it seemed to run okay. he rode it 5-6 different time putting a total of 3-4 hours on it and the SC failed again....

    After he pulled it apart again he realized the flywheel had been damaged and that was why the SC had failed the second time.

    this winter he decided to ditch the GTX hull in favor of the RXP hull...

    He started with swapping the engine into a 04 Rxp hull and from there it morphed into a full stage 3+ build.
    build thread here

    After getting the RXP out it blew a coolant line to the rideplate and overheated again....... Both times it over heated he was forced to ride it in...first time was almost a mile of starting it then shutting it off/ starting it/ shutting it off....repeat, repeat, repeat.....

    the second time it happened it was only about a 1/2 mile so not nearly as bad...

    since putting it together he has changed out almost everything known to man with the exception of the long block...

    current numbers
    AFR is 11.7 WOT with a base of 56 on the RRFPR
    48s wouldnt flow enough fuel at 75+psi to fuel it at 7500 rpm.. ( i dont understand this!)

    Ski info
    05 GTX LMTD 215 engine with 490+ hours
    04 RXP hull/ engine harness/ mpem/ 05 GTX cluster.

    Compression test shows 120, 107,120 psi.
    he did do a leak down and i think he said it showed like 50%.... But i need to verify that #.

    Engine Mods

    4in front air
    Fresh 2 rude with slip set to 18lbs
    XS IC
    Modded water box
    thru hull
    Riva ECU
    bosch 54s

    Hull Mods

    homebrew full size blockoffs
    solas 15/20R repitched to a 13/19
    riva grate
    bla bla bla...

    We have checked these items.

    compression. (120,107,120)
    leak down 50% (need to verify)
    have test with known working Rude 1 and 2 Rude
    Removed IC and lost almost 800 rpms
    Cam timing is okay
    Crank timing has not slipped
    tested stock ECU and Riva ECU
    tested with and without knock sensor update harness
    swapped out rrfpr/ injectors/ and fuel rails.
    advanced/retarded cam timing.
    even tested with a OEM 215 rxp prop and could only turn it to 7800

    Regardless as to what we do its a freaking TURD!!!!

    We are starting to think it may have a blown head gasket but it does not loose any coolant. he pulled the head off and said the HG doesnt look "blown" but it did have oil under it.... What could that mean???

    any help would be awesome!!!
    thanks in advance guys!!!

  2. #2
    keit29's Avatar
    Join Date
    Mar 2012
    Columbus, OH
    So he has 48s at 11.7 @ 7400 but any higher and he goes lean? My guess is he has a bad fuel pump. Does it have 400+ hours on it?

  3. #3
    keit29's Avatar
    Join Date
    Mar 2012
    Columbus, OH
    NVM, I read bosch 54s. I'm running a similar setup with stock ecu. 50s gave me too much fuel and I had to go down to 48s, still rich down low with a 55ish base pressure. I still think its his fuel pump dieing at high pressure. Also, if it helps my prop is pitched at 12/21.5 and I'm at 8160.

  4. #4
    You need to verify those numbers on the leak down test. If you truly had 50% on the leak down test your motor is your issue. The manual says 30 % but I think that is still to high for a strong motor. Your compression is the low side as well.

  5. #5
    wotxxxsd's Avatar
    Join Date
    May 2012
    A good leak down is 20% or less.
    50% and low compression is a major concern.
    1 too many over heatings will do that quick.

    Time to start fresh and rebuild her...

    Sounds like you know what your doing but now its time to start a rebuildproject...

    Get R done.....
    Rip on...

  6. +1 by:

  7. #6
    b_dolla44's Avatar
    Join Date
    Apr 2008
    Noblesville, Indiana United States
    leak down was in fact 50%

    So heres what he built today.

    05 70 hr head.
    2012 low hour valves
    2011 10 hour spring
    Les cooke retainers
    New oem head gasket
    New oem bolts
    05 rocker assembly...

    Hoping this clears it up....If not. I guess its time to do pistons and rings...

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