Dem old fuel pump blues again - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 19 (permalink) Old 11-06-2018, 05:53 PM Thread Starter
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Dem old fuel pump blues again

So after adding wheels, CF parts, Brembo bling and so on, I had the old girl running a couple months ago. Then I got an attack of stupid and decided to give some aftermarket coils a try. That turned into a 2 month long mission and after all sorted out I went to start and no start. She's spinning but no start. Checked the coil wiring and looks good so next try I'm like, what? No pump prime! Book says for 2002 RC check for battery voltage at the pump plug wire harness side, should have battery voltage for a few seconds. I have battery voltage but it's constant. Would this indicate fuel cut relay problem? I swapped with another relay, I also tried battery power to pump plug but no dice. Help me Obi wan you're my only hope.
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post #2 of 19 (permalink) Old 11-06-2018, 07:19 PM
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which wire did you measure for voltage on? you may have been misreading on the thermistor instead of the feed to the pump?



when you turn the key on does the FI light come on for a few seconds on the dash, then go out? if it does, then the fuel pump should prime, if it doesn't, then you have other issues we need to address first.



report back
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post #3 of 19 (permalink) Old 11-06-2018, 11:06 PM Thread Starter
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Thanks for quick reply. I measured 12.4v at the brown wire with black tracer & green wire. Also checked continuity from same br/bl wire from relay to plug at pump connector and was good. Fact that voltage was constant tells me no bueno. The FI did not come on when I turned key on. I have a used ECU and rear sub harness but were purchased online and never verified if ECU good yet. Just stocking up spares as new parts starting to dry up.
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post #4 of 19 (permalink) Old 11-06-2018, 11:39 PM
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If the FI light did not come on with the key on. The ecu is not powered up..

Check your kill switch and bank angle sensor
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post #5 of 19 (permalink) Old 11-06-2018, 11:46 PM
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The brown/black at the fuel pump connector is not the power wire. It's the fuel level sensor wire. If the thermistor in the tank is cold you'll see 12 volts on that wire. When the thermistor warms it lowers its resistance and connects the brown/black to ground and illuminates the low fuel lamp.

The power wire for the fuel pump is brown.



The brown black you were checking at the relay is not the power wire for the pump either. It is the negative wire from the coil on the relay. It goes to the ecu. When the ecu grounds it, it turns the relay on




So as I said, check your kill switch and bank angle sensor. Your engine stop relay is not pulling hence the no FI lamp with key on. This may not even be a fuel pump issue.
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post #6 of 19 (permalink) Old 11-07-2018, 01:31 AM Thread Starter
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OK so then the brown wire had no current. I did trim some plastic from the kill switch as the master cylinder was close and I wanted to give a little room there. That was a while back but very possible stressed a wire there. Will check in the AM and report back. Appreciate your help.
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post #7 of 19 (permalink) Old 11-07-2018, 08:50 AM
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With the key on, toggle the kill switch on and off. You should be getting a click from the engine stop relay (two reds and two blacks)

If you aren't, the issue is either a fuse or the kill switch or bank angle sensor. The kill switch can be bypassed by shorting the black/white and white/black at the 9 pin red connector on the right side.

The bank angle sensor can be bypassed by shorting the red and green wires in the green 3 pin connector on the left side of the tail section.
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post #8 of 19 (permalink) Old 11-07-2018, 03:22 PM Thread Starter
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Sorry, caught caught up in all our mid term election craziness this AM. Back in shop and checking out per your post.
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post #9 of 19 (permalink) Old 11-07-2018, 04:43 PM Thread Starter
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Relay is clicking. performed bank angle voltage check as per manual & 12.7V between green & white, .3V between green & red.
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post #10 of 19 (permalink) Old 11-07-2018, 04:52 PM
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Does the FI light come on then extinguish with the kill switch?
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