Fuel pump runs constantly - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 18 (permalink) Old 11-04-2015, 11:11 AM Thread Starter
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Fuel pump runs constantly

I've had this issue with my SP1 since I bought it 2 years ago, tried to do some research and found little help, apart from try swapping out the headlight relay with the fuel pump relay (?).
I tried that and it's the same, i.e. fuel pump doesn't prime and stop, just runs constantly, which I'm sure it is not supposed to do!
It doesn't seem to cause any issues though, I start the bike straight away, runs fine, etc.

Just thought whilst I have the fairings off I might as well ask the question since I signed up here!

Any ideas?

TIA
Stu
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post #2 of 18 (permalink) Old 11-04-2015, 03:01 PM
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if the rc51 is like other hondas, the ground for the fuel pump relay firing circuit is switched by the ecu. if the switch in the ecu has failed closed then the pump would run whenever the ignition is on.

see if you can find a friend with the same bike and swap ecus, i suspect this is the issue.

typically the switch in the ecu fails open, and the pump won't prime at all, but this may be a case of the opposite.


of course, if negative side of the really firing circuit is pinched/shorted to ground, you will have the same results.
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post #3 of 18 (permalink) Old 11-04-2015, 05:41 PM Thread Starter
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Ok thanks will check that out
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post #4 of 18 (permalink) Old 11-07-2015, 05:09 AM
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I would rather go and check what signals arepresent on fuel relay connector than replacing ECU- measuring signals on fuel relay connectorYou will get an answer if problem is relay related or harness/ecu failed, swaping parts is easy no brain involved task, try to be diagnostic guy and first try to adress were problem accured and then judge what part failed.just my 3 cents ....
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post #5 of 18 (permalink) Old 11-07-2015, 11:42 AM
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if the relay is latched then it has its positive. the negative is switched by the ecm

I didn't say to buy a new one, I said to try a known good one (borrow one from a friend)
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post #6 of 18 (permalink) Old 11-07-2015, 01:36 PM
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Listen. Even if my brother, let alone best friend asked to switch ECU's I think I would say no. Unless he is willing to buy a brand new one if mine gets screwed.
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post #7 of 18 (permalink) Old 11-07-2015, 01:40 PM
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listen, just because you don't understand the risk doesn't mean that it's a bad idea.



perhaps you could peruse the wiring diagram before you think plugging an ecm into a bike will blow it up.
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post #8 of 18 (permalink) Old 11-07-2015, 05:09 PM
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I do understand the risk. That's why I would never lend my ECU to anybody.
Who knows why his ECU malfunctioned. Putting my good ECU on his bike, could blow my ECU.

No thank you.
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post #9 of 18 (permalink) Old 11-07-2015, 07:34 PM
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thanks for your insightful advice for helping the OP. i'm sure he'll find it invaluable
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post #10 of 18 (permalink) Old 11-07-2015, 07:48 PM
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Get a wiring diagram & check the fuel pump relay connections to see if they're doing what they're supposed to, in particular with regard to the earth connection that should be made by the ECU. If that's constantly on with ignition on investigate with a continuity tester - it's possible someone may have modified the wiring at some point.

Having the fuel pump always on can damage it, which could someday leave you stranded.

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