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  1. #1

    Angry GTX RFI Diagnostics

    Hi any Computer specialists out there.
    I have purchased the BUDS computer out of frustration. my 2002 787 GTX RFI is in schmick condition. With two frustrating problems.
    1. It will start ever time without fail out of the water and run perfect. put it in the water and sometimes it will start after first compression, other times have to crank the living daylights out of it to get it started. totally randomly. However, over the last 4 weeks, i have found that its impossible to start after getting rolled upside down in the water. have to get the back out of the water to unload the engine then it will sputter and sound like its running on one cylinder until it gets revved up, then it will go normally again. WTF?
    ALL cables have been checked for resistance, grounds are good, cranking speed is great in and out of the water.
    2. I cannot get the TPS to go over 80%. All manuals suggest that to prevent fuel from being injected into the engine, one is to open the throttle full thus telling the computer that a flooded start is being attempted, and wont allow the fuel injectors to open. I have repeatedly tried to 'start the engine with the throttle wide open' and the engine always starts, suggesting to me that the computer needs above 80% throttle opening to activate the flooded start procedure. Am i on the right track?
    Max RPM i get in the water is 6500-6800, unless im airborne, then the rev limiter kicks in.
    I have replaced the TPS sensor, reset the TPS sensor, engine runs perfect. what am i missing?
    Is it possible to have a DUD MPEM or ECU that still works ok but only lets the TPS get to 80%

    Any help out there is appreciated

  2. #2
    AndinoWatercraft's Avatar
    Join Date
    Feb 2008
    Puerto Rico
    I'm no expert. That been said . I can advise to check your fuel pressure , engine compression also. You bought it new or second hand? Does the engine looks like has been serviced? This 787 RFI engines are a bit sensitive to moist and engine ground. The throttle cable when you open the hood has a nut for adjustment. Maybe adjusting there can get you the 20% that is missing. Not saying that's your main problem but could help solve the flooded mod issue. (sorry for my english lol) Before taking any guess check fuel press and engine compression and report back.

  3. #3
    AndinoWatercraft's Avatar
    Join Date
    Feb 2008
    Puerto Rico
    Almost forgot. When you get it to start check the charging system. Bad regulator can cause many headaches.

  4. #4
    Awesome, thanks heaps for the post. I do ALL the work myself. Im an aircraft engineer
    History is as follows, i bought the ski second hand completely unknown, not working with about 140 hours on it. It just had the stator windings rewound, i assembled it and it ran mostly ok. I rebuilt the engine at 170 hours bored to next oversize, new pistons, rings, new rotary valve, i even machined the valve clearance to manual spec. Following the rebuild, the engine ran no different at all until i bought BUDS and began doing the computer diagnostics myself. once i reset the TPS correctly, the engine behaved like a brand new engine with the exception of the starting problem in the water. There is absolutely nothing wrong with the engne, charging system or wiring. All of the electrical grounds are less than 1 ohm between, computer grounds on the generator case, to cylinder head and battery negative. i have checked every resistance there is to check between engine sensors and computer. TPS resistances are within spec. battery voltage reaches 13.5 - 14v. The butterfly makes full travel idle stop to WOT stop, new throttle cable. The one thing i havent checked yet is fuel pressure.
    Do you know if the ECU should only go to 80% or should it go to 100%? This is the only odd thing i cant figure out. I would love to get my hands on a known good ECU and see if it does the same thing. but dont know anyone else with a 787 RFI.
    I have a feeling the hard starting in the water has something to do with the TPS 80% issue. maybe not related but caused by the same issue. like a faulty MPEM or ECU.
    Thanks again for any kind of input

  5. #5
    Meantime it has about 210 hours on it. love getting out on the ski

  6. #6

    Join Date
    Oct 2011
    Foley Alabama
    Have you checked your rotory valve timeing?

  7. #7
    Thanks for the suggestion,
    No, thats not it, i fitted a new Rotary valve when i rebuilt the motor and paid special attention to the timing and the clearance.

  8. #8
    yamahadoo's Avatar
    Join Date
    Sep 2012
    Gulf Breeze, FL
    Its not uncommon to see only 80% TPS.. I think its excessive rotary valve clearance. You can test it by starting the ski on the trailer and then apply back pressure by putting a shop rag over the exhaust. The sooner the engine stops the worse off the valve is .. It should be difficult to stop the engine. I use this test often. just fixed a RFI that was hard to start because of a pitted and worn out intake cover.

  9. #9
    Great! Thanks!
    good to hear that others are only seeing 80% TPS @ WOT aswell. Will give your test a go. I checked fuel pressure yesterday....Perfect from idle to redline.

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