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  1. #1
    Click avatar for tech links/info, donation request K447's Avatar
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    Arrow Variable/uneven throttle response on Ficht 2002 Virage TXi

    Well, I am sure I have missed something obvious, but here goes;

    One of my 2002 Virage TXi machines is running great, with one nagging exception. Starts instantly, idles smoothly, will pull to 6900RPM and circa 60mph, with no misses or surging at full throttle. New NGK spark plugs.

    The problem is at low-mid range it will sometimes, but not always, not respond smoothly to the throttle. If I hold the throttle constant, the engine RPM will bump up and down some. It never threatens to die, and will always respond to a strong squeeze with immediate power.

    I swapped the spark plug wires between my two Virage TXi, and that made no difference.

    This is the third TPS I have installed on this engine, and the symptoms have not changed.
    I tightened the contacts in the TPS connector, and that made no improvement.

    The problem seems to occur a little more when the engine is cold (I have a speed restricted channel where I launch), but I may be imagining the difference a warm engine makes.

    I might add that I am not at home where most of my tools live, so I have only basic tools (not even a ratchet socket set ) and a simple multi-meter with me.

    What can I check, or swap between the two machines (I have both 2002 Virage TXi with me), using only simple tools and diagnostics?

    I would like to figure out what the problem is, even if I can't fix it right now.


  2. #2
    Bernie's Avatar
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    Keith
    Change air temp senders over it is in the airbox where the air cleaner sits .Check to see if it is damaged .check the resistance in the crank sender while you are there
    Bernie

  3. #3
    Click avatar for tech links/info, donation request K447's Avatar
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    Swapped air temp sensors (exchanged the airbox base plates, actually).

    Swapped CPS (Crank Shaft Position Sensor) sensors.

    All sensors checked out within spec for resistance (ohms), and matched between the two Virage TXi.

    No change in operation, still stutters at part throttle (circa 1500 to 4000 RPM).

    Still 6900RPM at WOT, smooth at full power.

    Any more ideas?
    Last edited by K447; 07-17-2008 at 07:12 PM.

  4. #4
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
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    Could there be any grounds that aren't giving consistant resistance,that in return could be causing false readings to the EMM?

  5. #5
    Bernie's Avatar
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    check back of tps connector on the loom side .I think there is a connection issue from tps to emm .Might have a chat to you over weekend

    Bernie

  6. #6
    Click avatar for tech links/info, donation request K447's Avatar
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    Well, I will check them again. I did remove, clean, and refasten the engine block ground bolt recently - no change in symptoms.

    Starts instantly, every time. Idles without a hiccup.

    What is mystifying me is how it works so well at idle, and at full power.

    Just the mid-range is lumpy, which I would normally think was the TPS. Three TPS later, same problem!

    Noticed the problem during a test ride last year, since then new NGK plugs, new TPS, swapped ignition wires, and now I've swapped CPS and air temp sensors.

    Compression is good, power is good at WOT. Fuel economy seems good.

  7. #7
    2000 pro 785 (son's) 1998 pro 785 (dads) old guy in mich's Avatar
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    ficht is direct inject is it not?
    believe it or not think i read somewhere that plug placement was very critical to smooth operation. seem to remember too that plug spacers are available in various thickness to properly aline them. something with fuel spray vs electrode placement. seems to me randy might have sold them. look like regular plug washers only various thickness.
    take it for what is worth not even sure it applies.

  8. #8
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
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    Indexing the plug... Could be.

  9. #9
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by old guy in mich View Post
    Ficht is direct inject is it not?
    Yes, it is direct fuel injection into the cylinder head.

    ...I read somewhere that plug placement was very critical to smooth operation.
    seem to remember too that plug spacers are available in various thickness to properly align them. something with fuel spray vs electrode placement. seems to me randy might have sold them. look like regular plug washers only various thickness...
    Spark plug indexing washers - I understand what you are saying, but in my case the problem remained after new NGK spark plugs were installed, so I don't think the spark plugs are badly indexed, and getting flooded by the injector spray.

    Bernie reminded me of some additional troubleshooting techniques, which I should have done already, but just didn't think of them.

    In the morning, I will be firmly strapping it to the trailer front and rear, backed into the water. Remove TPS from throttle body, start engine, then tie the thumb throttle wide open.

    On a carb'ed ski, this would probably launch the ski into my car trunk. Being Ficht, with the TPS not connected to the throttle shaft, the engine will continue to idle, with the throttle plates wide open.

    Now I can slowly turn the TPS by hand, and watch the engine RPM. Since the TPS is no longer mounted to the vibrating engine, I should be able to determine if the unstable part throttle RPM is due to a vibrating TPS wire harness or connector.

    If the problem is minimized or absent, I can then start hunting for the intermittent connection in the TPS wiring.

    If the problem doesn't change, then I will know it has nothing to do with the TPS wiring near the engine.

    I will also check injector DC supply voltage during the mid-throttle range, to see if it drops or is unstable.

  10. #10
    SPEED KILLS, BUT YOU GET THERE QUICKER Keddano's Avatar
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    Gotta love the internet and Bernie. Good Luck.

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