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Discussion Starter #1
2005 C50T has power at harness connection to fuel pump relay but no power at harness connector to fuel pump. Relay checks good, according to Clymer manual test. The wiring diagram shows a yellow wire that leads from the pump to the ecm and also to the relay. I am guessing the ecm activates the pump through this connection. Does anyone know a way to fault check this, or does anyone know what my next step should be? The engine will start and run with starting fluid, which claims to have upper cylinder lubricant, but I am skeptical and used it very sparingly. Also, the pump operates when voltage is applied to the tank wiring. I will appreciate any thoughts or recommendations.
 

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The third wire at the tank connector is for the low fuel light. The ECM just reads the resistance of that wire to ground, and turns on the fuel light when the fuel level drops below the sensor. The other two are ground and + power to the pump.

If the pump runs when power is supplied to the tank connector that's not the issue. The fact that it will engage the starter means it's not being held up by any of the safety switches that would also prevent the fuel pump running. Is the relay clicking/closing at key on/killswitch on? If so, have you verified there is +12v on the output terminal? Sometimes a relay will still click/close, but isn't making the connection internally. Use a jumper to take the relay out of the equation, and then see if you have power at the tank connector.

if it's not clicking, check for 12v at the trigger terminal. If you're not getting power to turn the relay on, I'd then check the fuse for the fuel pump (relay will not operate if that fuse is blown).
 

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Discussion Starter #3
When I bench test the relay with a fully charged battery the points close with a noticeable snap and there is continuity between the a and b posts.

With the relay in the circuit I can hear and feel a much smaller response to power applied. The battery is new and fully charged. I ordered a used relay from Ebay and the old one and the new one react the same way. I will follow your suggestion and by-pass the relay, while I await the arrival of a brand new one, also from Ebay. I checked the fuse with a test lamp and it was good. The only time I checked for power to the relay it was 12.5 volts but I am going to check it again. I cleaned the frame ground and get 12.75 volts when I test at any point on the frame.

I have not checked for continuity or resistance in the wires from the relay to the pump, something I should have already done but I will.

Are you familiar with the way an ecm fails? Does the whole thing go at once or is it possible for only a portion to fail?

Once again, I sincerely appreciate your help.
 

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ECU failure on modern bikes is quite rare, although not unheard of. It's always the last thing in troubleshooting charts, and diagnosis is usually "replace with known good". In several years of working as a tech at a suzuki/bombardier dealer, I don't recall ever swapping an ECU. Odd electrical issues were usually caused either by a crappy battery/low voltage, bad grounds, or loose/damaged harness connectors. Carefully inspect the connectors, that the pins inside aren't damaged/bent/loose/pushed in on both the male and female sides. I have run into pins that get shoved back, from a cursory glance the wire appears intact but since the pin is shoved back, doesn't make connection when joined. Give each wire a gentle tug and wiggle to make sure it is fully seated into the connector and isn't loose.

I'd rule out absolutely all possible other issues before looking at trying a different ECU. A small amount of voltage loss through the harness is normal when compared to direct to the battery.
 

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Discussion Starter #5
Thank you once again. The info about the ECU was good news. I had begun to worry about it. I haven't been able to get to the bike since your last message but my approach will now be to start over and not leave a possible problem area until I have satisfied myself that I have done my best to clear it. I will report back when I figure it out, hoping what I learn will be helpful to someone else.
 
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