I need help: Fuel Pump - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 75 (permalink) Old 06-10-2018, 08:17 PM Thread Starter
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I need help: Fuel Pump

Yea yea I know... I usually answer these types of questions, but my fuel pump isn't working I don't have an SP2 Service Manual handy, I only have the SP1 Manual which brings me to my first question:

1. Is the wiring diagram for the SP1 the same as the SP2 in regards to the fuel pump, bank angle and relays etc?

2. Isn't the middle wire on the fuel pump plug the only hot one?

I let the fuel pump sit dry for a few months and I am afraid that it has locked internally as I have had this happen before with the nasty ethanol fuel we have to use. Got lucky and just had to beat on the fuel pump a bit with a rubber mallet and it started working again. but faaack I don't want to take that pump out of the tank again so I want to confirm the electrics are proper before going after the fuel pump directly.
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post #2 of 75 (permalink) Old 06-10-2018, 08:49 PM
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I believe the sp1 and 2 are wired the same as far as fuel pump and kill logic go.


I just went over exactly this with a guy earlier today



First thing to do is verify the engine stop relay is working. Just hold the relay in your fingers and feel for a click when you toggle the kill switch

If the engine stop is clicking, do the same with the fuel pump relay. Check for a click on, then click off a few seconds later


If the engine stop clicks with the kill switch but the fuel pump doesn't, check that the wiring to the ecu is in good shape, the brown/black is provided a ground by the ecu to run the fuel pump relay.

If both relays are clicking and you have verified 12vdc on the black/white wire, chances are it's the pump.


The power to the fuel pump comes off the fuel cut relay on a brown


The low fuel sending wire is a brown/black.



Hope this helps
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post #3 of 75 (permalink) Old 06-10-2018, 08:55 PM
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Brown middle to fuel cut relay. Green ground of course and brown/ black to meter. So yeah should be hot.
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post #4 of 75 (permalink) Old 06-10-2018, 08:57 PM
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Quick draw Wibbly for da win.
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post #5 of 75 (permalink) Old 06-10-2018, 09:36 PM Thread Starter
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Well shit... Fuel Relay does not click (I have swapped all the relays and all of them click when used as engine stop relay.)

Fuel Relay:
Brown/Blk wire to the fuel relay is 11.9v hot from the ECU with the key on.
Brown wire from the relay never goes hot
Both Blk/Wht wires to the relay are 13v+ hot


At the fuel pump:
middle Brown/Blk wire is 12V
Brown wire is cold

Looks like I am gonna be up awhile... I had forgotten how much I hated working on these things and even more how much I hate looking at schematics.
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post #6 of 75 (permalink) Old 06-10-2018, 09:46 PM
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Mike, if the brown/blk is hot then the ecu isn't giving the relay a ground signal. It's got 12v on it from the black/white wire on the other side of the coil.


If you force this brown/blk to ground the pump will run.



Unplug the ecu connectors and check for poor connections or corrosion on all grounds and that brown/black


If all checks out, try a known good ecu.
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post #7 of 75 (permalink) Old 06-10-2018, 09:57 PM Thread Starter
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Just sat down and looked over the wiring diagram for the SP1. I see a mistake I have made already... I'll come back to this thread after I double check my own work...
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post #8 of 75 (permalink) Old 06-10-2018, 10:12 PM Thread Starter
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I may have fried the ECU when the wiring harness got munched. It did blow the 30A Red/Wht to the Bank Angle Relay...

Grounding the BRN/BLK spins up the pump like a boss
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post #9 of 75 (permalink) Old 06-10-2018, 10:30 PM
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that's too bad. the ecu is the last contact in the logic controlling the fuel pump so if grounding the brown/black lights up the pump, you've got something going on between the ECU and ground.


i would double check all the grounds anyway though. just set a meter to continuity and probe all the grounds in the ECU connectors to battery negative.
fortunately sp2 ecus are pretty plentiful, i'm sure you won't have trouble finding one.
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post #10 of 75 (permalink) Old 06-10-2018, 10:37 PM Thread Starter
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I still cannot believe I went to the trouble of yanking the tank and pulling the fuel pump though...
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