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Thread: Bad ECM

  1. #1

    Bad ECM

    The problem: When the key is turned on the fuel pump doesn't run ( whirly sound) and the bike won't start. I've discovered the br/bl wire on the fuel cut out relay field coil leading to the ECM has 10.5 volts on it , as measured from relay terminal to ground .
    When I ground this wire the fuel pump runs as long as the wire is grounded. I've swapped relays with known good ones it's definitely not the relay. There are no stored ECM faults, ignition and run switches are fine.
    *I fear this suggests I have a bad ECU!
    *
    Before I spend big bucks on one of these I could use some help with ruling out any other conditions that might cause this problem or prevent the ECM from pulling the br/bl wire low.
    *
    I'd like to understand
    *
    1) What shuts the pump of when the key is first turned on . ( ECM timing function I presume?)
    *
    2) Does the pump run continuously when the engine is running? With the engine is running, on my bike if I remove unground the br/bl while hile idling the bike runs 10 seconds max and gradually dies from fuel starvation
    *
    3) Could there be any other inputs to the ECM that prohibits the br/bl wire on the fuel cut out coil from being pulled low?
    *
    4)There's another br/bl wire that runs from the fuel pump (black connector) to the instrument cluster. What does this do? I've read its used to drive the instrument cluster. If so what voltage might I expect to read on this wire?
    *
    Any help would be greatly appreciated
    *
    Regards
    Joel Spano
    Rochester NY
    585-355-8366
    Attached Thumbnails Attached Thumbnails schematic fuel cut out.jpg  

  2. #2
    Natural Rider Enhancement Blrfl's Avatar
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    Re: BAD ECM

    Start with the basics before trying to diagnose problems that probably aren't there.

    What's the standing voltage of your battery and what does it sink to when you crank the starter?

    --Mark

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  4. #3
    Dave.David's Avatar
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    Re: BAD ECM

    Read about your FPR, Fuel Pressure Regulator. And check your power at the pump. Green wire needs ground , try using a jump wire from the plate atop the tank to a good ground. Good luck.

    Sent from my SAMSUNG-SM-G935A using Tapatalk

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    Re: BAD ECM

    Thanks David

    The fuel top plate ground wire has three tenths of an ohm resistance. I consider this a "good" ground.

    Battery voltage is 13.2 volts across the battery terminals key off no load.
    Power never makes it to the pump unless I ground the control wire leading to the ECU. However when the ECU control wire is grounded to force the pump to start there's 12.1 VDC available at the relay contacts which drops to 11.5-ish once the pump is running and the ground is maintained.

    To be certain I swapped the ST battery with my Gold wing battery ( known good unit).I'm moving past battery voltage and supply voltage at the pump for now. For record the current draw from the battery thru my amp meter is 5.6 amps when the key is turned on and about 9.6 amps when I force the fuel pump on this seems reasonable to me.

    As far as the fuel pressure regulator is concerned this is a purely mechanical device using a spring pressure and diaphragm mounted to the fuel rail and which serves to bypass excess pressure created by the fuel pump back to the tank and maintain a relative constant pressure in the fuel rail for the injectors (in my case 55 psi) . However, before the system can build fuel pressure the fuel pump has to run which is my dilemma.

    If I've misunderstood the Fuel pump regulator enlighten me.

    Keep the suggestions coming they're a lot cheaper than a new ECU .

    Thanks
    Joel

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    Re: BAD ECM

    Oh yes I forgot to mention the current readings were measured with the head light fuse removed.
    Don't want to kill the battery during all the troubleshooting.

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    Re: BAD ECM

    Just a long shot but the fuel pump wont run if the engine cut-off switch is off. Maybe check the contacts in the switch and the wires that effect the pump?

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    Re: BAD ECM

    Quote Originally Posted by jspano01 View Post
    Keep the suggestions coming they're a lot cheaper than a new ECU.
    I'd suggest answering the second half of my question: How far does the battery voltage fall when you crank the starter?

    --Mark
    Wizzzzzzzzzzzz What's a Blrfl? ... Shameless plugs: STWiki

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    Site Supporter woodybelle's Avatar
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    Re: BAD ECM

    I am just guessing here but does the ecm need to see the tip over sensor before allowing fuel to pump?
    Jerry Bellefeuille:
    2006 ST 1300

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  11. #9
    L Plate Rider TerryS's Avatar
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    Re: BAD ECM

    The second wire from the pump connector to the instrument console is used for a low fuel warning light, nothing to do with the pump aside from sharing the ground connection.

    AFAIK the fuel pump relay is solely driven by the ECU, and it should be energised for a few seconds when you turn the key on, and then constantly when the engine is running.

    I think Woodybelle is probably correct that the ECU needs an input from the bank angle sensor as well before allowing the pump to run. My understanding is the bank angle sensor is intended to stop the engine in a tip-over, and it would make sense to stop the fuel pump in that instance too. The BAS provides a ground path that allows the engine stop relay to energise.

    So next step would be to locate and test the Engine Stop Relay.

  12. #10
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    Re: BAD ECM

    Thanks Terry


    You're the first guy to provide a definitive a statement on theory of operation. Thank you !

    The confirmation of the wire leading from the pump to the instrument cluster for low fuel only is helpful.
    I suspected the ECM timing for closing the fuel cut out relay at "key on" and during engine but having it verified is comforting. Now I can move forward with confidence.

    The bank angle is providing power to the adjacent fuel cut out relay and the ECM on the black and white wires .
    With the key on , engine run switch on, I measured 12.2 volts on the Grey 23 pin ECM connector (ECM removed ) the two black/ white wires provided this voltage from the bank angle sensor relay contacts.

    The engine start stop switch provides power to the bank angle sensor and relay and since this relay energizes and remains energized I believe the start stop switch ,the bank angle relay ,fuel cut out relay , and ignition switch are all good.

    Checking for proper ECU grounding:
    Measured continuity on the black 23 pin ECM connector ( ECM removed ) good continuity on green /pink and green /blue wires leading to ground. (i.e. .3 ohms )

    The ECM is for sure failing to drive the brown / black wire low on pin 4 leading from the fuel cut out relay to the ECM. The engine will start and run indefinitely ( Ĺ hour run time check so far ) as long as I ground this lead .

    Iím running out of things to check.

    Regards
    Joel

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