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Pump primes, bike starts, pump starts, engine runs for 1 second at ~1K rpm, another second engine misfires, 3rd second engine runs with a few cylinders lean firing, stalls on the 4th second, pump stops.
I just quickly scanned the thread so forgive me if I missed something.
From the schematics I've been looking at, the fuel pump relay is controlled by grounding the negative side of the fuel pump relay coil. The other side of the coils is 12 vdc when the key is turned on. The negative side of the coil is pulled to ground by the ECU, energizing the fuel pump relay. Obviously you hear the pump so we know the relay is energizing and passing current through it's contacts to the fuel pump. What we don't know is, whether the ECU is stopping the fuel pump, so I have an idea.
There is a wire at the ECU colored blue with a yellow tracer. This wire will be blue with a yellow stripe or yellow dots. Since I haven't seen any fuel pressure regulation I'd imagine it's done within the pump itself. set your meter to measure 12 vdc.Put the voltmeter positive lead on the blue with yellow tracer wire coming from the ECU. The negative meter lead goes to negative on the battery or a good engine/chassis ground. Start the bike and watch the voltage on the wire. It should stay at zero volts. If the voltage climbs up near 6 -12 volt the ECU is floating the ground which de-energizes the relay. This is probably due to a sensor input signal to the ECU and it thinks or knows something is wrong. If this test shows the ECU is lifting the ground you might want to try this. Disconnect the blue with yellow tracer wire from the ECU. Ground the blue with yellow tracer wire coming from the fuel pump relay. The ECU should not be attached to this wire when doing this!
Turn the key on. Does the fuel pump prime and shut off? If yes. start the bike. Does it run? If yes shut it off and remove the grounded wire and reattach the blue wire with yellow tracer to the ECU as it was originally. At no time should you ground the ECU side of this wire. If it runs you've now confirmed the fuel pump works and there is probably a sensor/logic problem.
Try this and get back to us!
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