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Thread: Intermittent Electrical Fault

  1. #1
    rabid reader dbrick's Avatar
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    Intermittent Electrical Fault

    My ’96 RS with 104K has an electrical problem - I think it's an electrical problem - and I’m stumped in diagnosing it.

    Earlier in the spring, the motor occasionally cut out when warm, but immediately restarted. Finally, it began exhibiting the classic HES wiring symptom: it would only restart after cooling off. I removed the HES plate, and replaced the sensors and wiring as Dana Hager describes. The plate-and-harness combo worked fine on the bench. I removed and inspected the HT coil and wiring, and found no cracks or other suggestions of problems. Reinstalled, the bike started right up and ran well.

    I’ve been riding it to work again for several weeks. After a week, it cut out on the way to work one morning, only a few blocks from home. It restarted immediately, and didn’t quit again. Thinking about the job (“Look where you last worked”) I realized I hadn’t done a good job on the connectors. Last weekend I pulled the tank, did a thorough Deoxit job on the HES wiring harness plug-and-connector, the fuel tank wiring plug-and-connector, the two FI injector connectors, and removed and reinstalled the main CPU plug as well a few times for good measure.

    Monday and Tuesday, it ran fine. This morning, the bike quit again just after leaving home. It restarted immediately, then quit again a block later. Again, it restarted immediately, and didn’t falter coming home at the end of the day.

    During all three morning quits, the RID stayed on; I conclude the problem isn’t in the sidestand switch, kill switch, or their wiring. Because it was still in gear and fired right up when I squeezed the clutch and hit the starter button, I think the clutch perch switch and wiring are OK. The alternator light came on when the bike stopped running, and the bike restarted without jiggling the key or turning the ignition off and on, so I think the problem isn’t the main power feed in the ignition switch. The battery is a near-new (<4 months in use) Odyssey, and the bike always cranks briskly.

    If the problem were the common wiring harness fault (too tightly Zip-tied to the frame), you’d think sometimes the motor would quit at other times, or in response to handlebar movement, or wouldn’t always restart immediately. But it doesn’t. it always starts immediately, runs well, and shows no symptoms other than these three (so far) cold-engine quits.

    As I mentioned, after rebuilding the HES tested good, and 99% of the time it operates correctly.
    Still, as far as I can see the quits are only consistent with a second but different HES fault.

    Any ideas what it might be? Any ideas how to move further with diagnosis?
    Last edited by dbrick; 05-27-2010 at 04:20 PM.
    David Brick
    Santa Cruz CA
    2007 R1200R

  2. #2
    Hi Dave:

    I had one of these long intermittents on my Yamaha. I ended up wiring in some LEDs so I could see where there was power(and not) when it went dead.

    Ride with extra care, you don't want to have it cut out when you're merging with fast traffic!
    Mike Marr
    1978 Yamaha XS750 (Needs rings), 1996 BMW R1100RS, 2004 Honda CRF230F

  3. #3
    rabid reader dbrick's Avatar
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    Thanks, Mike. It helps to know that others have been there before.

    Tell me more about how you LED'd various circuits, and which ones you selected.
    David Brick
    Santa Cruz CA
    2007 R1200R

  4. #4
    Well, what would you like to know when it cuts out?

    I'd like to know if the fuel pump had power or not. So a LED on the output of the fuel pump relay.
    There's also a relay that switches 12V to pin 33 on the motronic unit. That relay is controlled by the side stand/clutch switch logic.

    Since both of these lines are looking at relay contact faults, maybe swapping those relays with the horn relay would be simpler.

    If you haven't already swapped the fuel pump relay it might be a good suspect. Old high current contacts in vibration...

    Know what? If a new relay was less than $20 I think I'd just change the fuel pump relay next.
    Mike Marr
    1978 Yamaha XS750 (Needs rings), 1996 BMW R1100RS, 2004 Honda CRF230F

  5. #5
    rabid reader dbrick's Avatar
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    The LED monitors are clever!

    Reading your "replace the fuel pump relay" comment, I'm reminded of a similar challenge I had in an older Saab 900 that'd stop running in the same way. In that car, the problem was in way-hidden wiring that controlled the fuel pump relay - I carried a jumper for a while, so that I could pull the relay and connect the output sockets directly. But the bike's relay itself, as you say, is certainly suspect because of age.

    Onward!
    David Brick
    Santa Cruz CA
    2007 R1200R

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