Help with no tach & engine light

Discussion in 'Electrical' started by hdflash, Jun 28, 2013.

  1. hdflash

    hdflash Member

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    Looking for suggestions on this problem.
    1999 FLHTCUI (Magnetti-Morelli).

    Starts & runs but idle’s a little low.
    Tach does not work.
    Engine light on after start up.
    Trouble code 35 (tachometer), no other codes. I already know the tach doesn’t work.

    Wires to tach:
    Black, ground, is good.
    Red, power, has 12 volts.
    Pink, trigger, has no voltage.

    Not sure where to go from here. Seems as though tach should work if it gets signal from trigger wire. ECM must be getting some kind of signal or else it would not be able to fire and run the engine.

    Where does ECM get signal from to give signal to fire coil? Cam position sensor? Crank position sensor?

    Does ECM throw trouble code to show tach not working but everything else OK?

    Any help would be greatly appreciated.
     
  2. Webbtron

    Webbtron Banned

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    if the engine light comes on for like 8 seconds after starting then you have a historical code. These are covered in the manual, if you have one. The tach might be a second issue. In my case I had to go to the dealer to get the historical code cleared. If you don't have a manual. I'll have to go out to get mine
    [​IMG]
     
  3. hdflash

    hdflash Member

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    As I stated, the code is #35, "Tachometer".
     
  4. Webbtron

    Webbtron Banned

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    If the check engine light comes back on for 8 seconds after the bike starts you have a functional error. These errors can only be retrieved by the dealer. They are codes 52 - 55.
    I understand you have a tach (#35) error in addition to this but if you have the manual it will explain the functional code better than I can type them. Do you have the manual?
     
  5. Hoople

    Hoople Account Removed

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    Both sensors are used and both must be working in order to fire off the coil. Lets say you want your spark to fire 5* BTDC. The crank trigger fires the spark at the precise degree you want before TDC. In this example it would be 5*.

    The cam sensor makes the spark fire in the correct phase of crank rotation. Meaning it prevents the spark from firing at 5* BTDC of the exhaust stroke and allows the spark to fire 5* BTDC on the compression stroke.
     
  6. RibEye

    RibEye Junior Member Contributor

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    Where is the cam sensor on the newer twinkies?

    Enjoy,
    Rich P
     
  7. hdflash

    hdflash Member

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    Webbtron,
    Engine light comes on after start up as a result of no tach signal and stays on, hence the 35 error code. Although I’m unsure of how the ECM “knows” the tach isn’t working since it must be getting a signal from the cam & crank sensors in order to properly run the engine.
    The errors are fairly easy to recover without going to dealer. Error 52 is “ECM RAM Error” and error 55 is “Microprocessor Malfunction,” neither of which are problems here. The bike seems to run fine other than the tach not working. And yes, I do have a manual.

    Hoople,
    Thanks for the explanation. Now I just have to find out why the tach isn’t getting a signal from the ECM.

    RibEye,
    The newer twin cams do not use a cam position sensor. The bike I’m working on is a 1999 and has the Magnetti-Morrelli system not Delphi.
     
  8. Webbtron

    Webbtron Banned

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    Sorry I should have read closer that the light was staying on. But I thought the ECM might be the problem. My tach is a bolt on so it is different that yours. The manual says to use a break out box and wiggle the wires or the dreaded scanilizer. At least there are only 3 wires with the pink going to the ECM. Again I learned that the after market "scanilizers" don't work on our stuff, which is why I had to pay the $45
    Again I using a 2000 manual but I think they are more identical than not.
     
  9. hdflash

    hdflash Member

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    Does anyone happen to know whether this tach works with a pulsating signal like all the older ones or does the ECM send a variable amount of voltage to show the RPM's?
     
  10. RibEye

    RibEye Junior Member Contributor

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    It is not an analog signal (varying voltage). The signal is pulses, and the pulse rate increases with rpm. The tach internally converts the pulse rate to an analog voltage, to drive the meter movement.

    Enjoy,
    Rich P