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  1. #1

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    Still stuck at 8000 RPM with 8650 redline Rotax full Race ECU - knock sensor help

    Can anyone point me to where exactly on the harness the knock sensor resistors are located? I found the bulge on the end of engine harness knock sensor connector, but thats not the resistors. The knock sensor cable is actually very smartly a single wire core shielded with an outer wire that turns back into 2 wires at the "bulge" junction. I've felt through the wiring on every harness I have, and can't find anything but wires, no resistors anywhere...

    It wont even go past 8000 when it comes unhooked so I know I'm not propped out, I'm stumped... Anyone got any other ideas? Or can tell me exactly where these resistors are on the engine harness? Thanks!


  2. #2
    Moderator beerdart's Avatar
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    Measure the resistance of the harness from the ECU to the Knock plug.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  3. #3

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    Thanks Beerdart, I've just been lazy. Its a pain in the ass to do without that dealer pinout ECU connector contact tester.

  4. #4
    Got Boost? psycho rxp's Avatar
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    The picture he posted (the right one) just below the ECU mount plate, where it's thick (bulge) should be where the bypass is to be done.

  5. #5
    Having Fun jp1300r's Avatar
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    Help me understand something. I see you are running a Rotax Racing ecu. I thought they didn't use the knock sensor/control in their ecus.

  6. #6
    Got Boost? psycho rxp's Avatar
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    they don't, And that would be a reason for the low RPMS if it was hooked up with the resistor, or pigtail adaptor

  7. #7
    Having Fun jp1300r's Avatar
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    Quote Originally Posted by psycho rxp View Post
    they don't, And that would be a reason for the low RPMS if it was hooked up with the resistor, or pigtail adaptor
    Okay, I see what you are getting at. I don't know anything about Rotax Racing ecu.

  8. #8
    Richieb's Avatar
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    Another way is the cable to work it out.

    On the end of the cable that goes to the exh temp sensor, there is a small sticker folded on the cable.

    IF.. it has a date on there 2003 or later, the engine loom has the resistor in there, if 2002, then you may need the Piggy cable.

    The wroting is a little hard to see, but this seems to be the norm, and can be clearly seen if you look carefully.

    The in-built resistor is tiny, and can be hard to feel in the loom.

  9. #9

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    Ok, pulled out the multimeter and a few wiring harnesses last night. one an 02 harness, another dated 12/03, and one dated 2/04. According to the service manual, even the second connector without a resistor in the line should have ~18k ohms resistance, but all 3 harness showed basically no resistance on either connector. I mean 0.001 resistance on both wires, and I'm using a multi hundred $$$ Snap-On multimeter, so I trust the readings. Anyhow, doesn't agree with the service manual, but I know there's no resistors in the harness anyway. So I'm going to swap out the engine harness on my ski for this one, and bring along a spare knock sensor too (Ski is on the lift at the lake currently) and see what happens. Actually about to head there shortly, so I'll report back tonight, and I'll report what happens. I'm going to swap pumps/props as well so I can add my 2" extension with Pump pressure relief, so I don't die

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