Fuel pump relay failures

Discussion in 'GS Boxers' started by DLvid, Mar 8, 2013.

  1. DLvid

    DLvid Adventurer

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    Hi all, I've read many posts that relate to failed fuel pump relays and my story is very similar. My question is what is causing the relay to fail? Specifically the relay is damaged (not visibly) and won't work again. What is happening in the circuit that can short the relay but not blow the fuse?

    Some background: Riding at 70 on the FWY, bike suddenly lost all power. After successfully not having a bigger problem, power suddenly resumed after about ten seconds. Rode another sixty miles without incident. At end of day got on bike to ride home and no fuel pump prime with key on. Swapped fuel pump relay with horn relay and got home.

    Bike is an 02 GSAdv with 50K miles.

    I figured it was just one of those things until it happened again several rides later. Went to start bike and again no fuel pump prime.

    Those of you that have had this failure can you report back where you finally found the failure point. I'm going to start at the kill switch and pay close attention to tight zip ties but as you know trouble shooting a wiring harness is not easy. And just for fun, I may pull the HES and check that too...

    Thanks for any input.
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  2. roger 04 rt

    roger 04 rt Long timer

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    A couple questions:

    Have you tried putting the bad relay back in?

    The fuel pump relay powers the fuel pump, fuel injectors and O2 Sensor Heater. Do you have a Powercommander, Techlusion or anything else attached to the injectors?
    #2
  3. fallingoff

    fallingoff Banned

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    on my son's bike he had a erratic fuel pump operation

    i tracked down to the wire into the tank

    goes thru plastic

    wire was broken inside the plastic

    so it would work sometimes

    just moving the bike and changing the relay

    just a thought

    cheers
    #3
  4. DLvid

    DLvid Adventurer

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    No, nothing attached to the circuit.
    I tested the 'failed' relays and they still 'work'. Putting 12v to them causes them to close as normal but they will not allow the fuel pump to prime. VERY odd. Resistance across the coil is 6 ohms instead of the new relays 1 ohm. There is some micro pitting on the contact closure (found after removing relay from shell). Perhaps there is too much current being drawn... I need to measure the voltage at the relay socket next.

    I have installed the new part number relay and it's working (for now). It's not a good feeling when you can't trust your electrics!

    Haven't found any shorts yet but will continue to check.
    #4
  5. JimVonBaden

    JimVonBaden "Cool" Aid!

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    More than likely your relay was bad despite appearances. It is not that uncommon.

    Jim :brow
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  6. DLvid

    DLvid Adventurer

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    One bad relay I'm ok with. I put the horn relay into the fuel pump position and after a few rides it failed too...
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  7. JimVonBaden

    JimVonBaden "Cool" Aid!

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    If that is the case, it is likely that your pump is failing! A failing pump can cause excessive draw and burn up relays.

    Jim :brow
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  8. roger 04 rt

    roger 04 rt Long timer

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    Jim, That's a pretty good bit of trivia.

    Do you happen to know if the running current is higher, which is easy to measure; or is it the momentary starting current that causes the damage?

    With the double relay failure on his bike, should he just replace the pump or is there a test he can make?

    RB
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  9. rdwalker

    rdwalker Long timer

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    I am not 100% sure if it is a bad pump, though it is very likely. Some further troubleshooting would help.

    Here are my thoughts (from being in the electronics "biz").

    The fuel pump is protected by 10A fuse. If that value is still in the socket (worth checking if it is), than it should blow by about 15A. I don't know the specs on the actual relay, but that style relays are typically rated 20-30A. All this means that steady over-current by pump should not damage the relay; fuse should go first.

    This is, by the way, extremely easy to measure. Plug an ammeter capable of 10A-20A into the fuse socket, see what happens. There may be some very brief inrush that is faster than fuse clearing time - indicating a bad motor.

    There could be some intermittent short in fuel circuit wiring. It's worth inspecting the harness. On an R1150, the green/white wire from the relay feeds:
    - the fuel pump
    - plug for evaporative control valve ("carbon canister")
    - fuel injectors
    - O2 sensor
    Lots of stuff to go bad. Connect an ammeter and jiggle the harnesses.

    Finally, there could be a sparking problem. Bad fuel pump motor could cause excessive sparking when being turned off, eroding relay contacts. It's an inductive kick-back; usually there are snubbers to contain that, either the snubbers or the motor could be bad. There is no easy test for that for a home mechanic, pump replacement would be the way to go.
    Fuel injectors have less inductance and are less likely to generate a damaging spike. But, maybe one is failing? Pull the sparkplugs to examine, see if there is difference between cylinders.

    Good luck troubleshooting. Robert.
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  10. JimVonBaden

    JimVonBaden "Cool" Aid!

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    It is likey the pump is drawing more current when it runs. That fact that it does not run constantly would mean that the higher current is causing damage to the contacts every time it starts. This would lead to faster wear. Really high current would mean very fast wear!

    Jim :brow
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  11. JimVonBaden

    JimVonBaden "Cool" Aid!

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    All also true and possible!

    Jim :brow
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  12. baloneyskin daddy

    baloneyskin daddy bikaholic

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    Could there be a problem with the fuel pressure sensor that is allowing the fuel pump to overwork itself to the point of a current over draw.
    #12
  13. rdwalker

    rdwalker Long timer

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    On the R1150, there is no fuel pressure sensor in the electrical circuit, pump is always powered.

    In the plumbing, fuel distributor regulator relieves excess pressure and routes it back to the tank. If it fails, there will be either too low or too high pressure at injectors, either would affect driveability.

    Regardless, overstressed pump would be continuously overloaded and should blow the 10A fuse. If it stays below 10A, it should not affect the longevity of relay contact.

    My feeling is that OP's issue is intermittent, as I mentioned above - not likely caused by the regulator. But, of course, that is possible as well. It all depends what tools OP has to diagnose his bike. Fuel pressure could be involved to measure.
    #13
  14. DLvid

    DLvid Adventurer

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    Thanks, guys. I will perform the checks mentioned and get back to you.

    The first thing I did was to replace the fuel pump. Nothing like spending $500 to cover a $15 dollar relay...

    This morning the headlights were not functioning, so I replaced the 'load relief' relay and they came back on. Any idea what the function of the load relief relay is?
    #14
  15. roger 04 rt

    roger 04 rt Long timer

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    When you press the starter button the Load Relief relay disconnects lights, horns, and heated grips. This reduces the load on the battery during starting.
    #15
  16. rdwalker

    rdwalker Long timer

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    This deed is done, but before you spend any more money on your bike parts, check for the available alternates to OEM. You'd be surprised how much you can save.

    A great source is Beemer Boneyard - not only used parts, but also many new ones. Here is the link. They do carry fuel pumps etc. for most models.
    Here is an example: oilhead Valeo starter motor is $200, Hall sensor $230.
    #16
  17. DLvid

    DLvid Adventurer

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    Hi all. Wow, it's been a while but the problem has been found. There is a diode related to the Motronic and most of the relays that was failing. My hat is off to Mike at Moto Marin for having the courage to tear apart the fuse box, find the diode, test it and confirm that when warm it was allowing voltage to flow in two directions (not what a diode does). Since this find and repair all is well.:clap
    #17