high voltage @ cam position sensor

Discussion in 'Electrical' started by GreenKing, Aug 22, 2012.

  1. GreenKing

    GreenKing Member

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    I need help to find out what to check next.
    I have a 97' FLHRI and am getting 7.15+ volts at the cam position sensor (should be 5.0), I have already melted one cam postion sensor and burnt out a EFI tuner (cheap BK model on closeout).
    bought bike 5 years ago, soon after noticed that the cam position sensor was melted and i replaced it. 4 years ago installed aftermarket V-Twinn tach-speedo, Bikers Choice EFI tuner, exhaust, air cleaner. 3 years ago burnt out the tuner and replaced with a Power Commander II and started looking for electrical problems. 2 years ago took bike apart and repainted and checked all wiring harnesses. Noticed that tach seemed to be reading odd rpm, 3,200rpm @ 70mph (thought it used to be 2,800 @ 70mph). only electrical addon is led tail lights.
    I am disabled and have only put 1200 miles on bike in the past 5 years. I would ride a little more now, but i do not want to burn out another tuner or cam position sensor or possibly something else.

    Any help on what i should check would be appreciated.
     
  2. Bodeen

    Bodeen Well-Known Member Staff Member Moderator Contributor

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    Welcome to the forum!
    What voltage do you have across the battery when not running? What voltage do you have across the battery when running? My first thought is voltage regulator but Hoople will be along shortly to give a complete run down on troubleshooting and the problem.
     
  3. Hoople

    Hoople Account Removed

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    The reference voltage is generated within the ECM and comes out of the ECM at Pin 16. It is a regulated DC 5.0v voltage regardless of of what the battery or alternator voltage is. That reference voltage is used on the TPS sensor, Baro pressure sensor, engine temp sensor, intake air temp sensor and cam position sensor. With that voltage being incorrect, all sorts of incorrect data is being sent to the ECM.

    I don't see it tied into the speedo, but my schematics on that year bike are not very clear. It is possible that the reference voltage is tied into the speedo, but I don't see it. It looks like you have a hall sensor for a VSS (ground speed) signal. If that is true, then the 5v reference is tied into that also.
    If you know your voltmeter is accurate, there is not a whole lot to check when the reference is not stable. If the reference is really high like you said, it's ECM time. Is the bike running at this moment?

    If a new ECM is out of the budget, you may be able to install your own outboard reference voltage power supply using a National Semiconductor LM7805 voltage regulator. You would have to be handy with a soldering iron, (can you build a Heath-Kit :)) be willing to invest a few hours of time, and risk spending about $40 because it always has a chance of not working out as planned.
     
  4. Bodeen

    Bodeen Well-Known Member Staff Member Moderator Contributor

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    I told you he'd be along! :s
     
  5. GreenKing

    GreenKing Member

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    :bigsmiley12: Thanks, thats great!
     
  6. GreenKing

    GreenKing Member

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    Yippie kiyay! more money! a new ECM is about $300? My bike does have just over 60,000 miles on it now and i vaguely remember that being the possible culprit in a thought process some time back (i have a bad memory from too many medications from my disability).
    Is there a test that can be done to verify a bad ECM?
    The bike IS running, and actually seems to run quite well. My only complaint is that the tach seems to be useless and the fact that i KNOW there is an electrical problem. I rode over 100 miles last weekend and no problems.

    I am comprehensive with my schematics, but my manual gives no voltages and the way they were organized is poor, a lot of flipping pages back and forth and marking pages with post-its.
    I am very sufficient with soldering, but probably just prefer to replace the ECM if that is what my problem is. I won't be able to do it right away, money is very hard to come by these days.

    In your opinion do you think it is okay to continue to ride if it is running well now?
    I just don't want to burn out my tuner or tach, i am almost positive that i have a hall sensor on the speedo pickup. I think i will just put the original speedo back in for now.

    Thank you for the insight and help,
     
  7. Hoople

    Hoople Account Removed

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    It's amazing to me that the bike runs good. On the TPS sensor alone, your telling the ECM your at WOT when your really at 1/2 throttle.. I would think the bike would have a ton of issues. Especially if the reference climbs up as RPM goes up.
     
  8. GreenKing

    GreenKing Member

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    I has great throttle response (with the tuner), and i play around when i ride too meaning i am not too old to have some fun with the loud pipes now and then. I also still like to race a little (with friends). like i said it runs great, is it possible that it is NOT the ECM?

    thank you once again,
     
  9. Hoople

    Hoople Account Removed

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    Yes, it doesn't have to be the ECM. It is remotely possible that something (especially aftermarket) on the bike has some internal leakage. Something like an aftermarket tuner, that uses BOTH the reference and 12 volt battery as inputs could easily pull up the reference voltage.

    With all the aftermarket black boxes out there, I can only diagnose the bike in bare bones factory trim. I mentally do not factor in any aftermarket products.
    That's the end users challange and problem.
     
  10. GreenKing

    GreenKing Member

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    Well, that is really what has me stumped. When i bought the bike it already had the cam position sensor meltdown issue in play with no aftermarket parts and no alterations or addons. So i am going to guess that the problem was already present before i added the aftermarket speedo/tach and before the air filter exhaust and tuner.

    It is very simple to disconnect the tuner and recheck the line voltage coming out of pin 16 on the ECM even though i really have doubts that that would have any affect on the output voltage to anything.

    Now the speedo/tach i could go back and disconnect because it did have some wire jumping to install it.

    I just keep thinking that the cam position sensor HAD to be getting too much voltage BEFORE i made any other changes to melt down like it did. ???