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Discussion Starter · #1 ·
I have a 2000 748 Standard model and I'm experiencing the same intermittent fuel pump failure that I've read so much about on the Ducati forums. My fuel pump is fine as are both engine management relays. The problem seems to be that the ground or -vdc connection for the relay coils is provided through the ECU. No problem at all with relay 1 (it provides power to the ignition coils). It's only relay 2 (fuel pump) that won't energize. The necessary +vdc is there for it. It appears that switching for that relay is done in the ECU and on the -vdc side of the relay. We call that sinking in industrial electronic control. If that's the case am I going to have to replace the ECU to resolve this?
Thanks
Mark in KC
 

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Your diagnosis is correct. Check for corrosion and clean (no dielectric grease please) the connector to the ECU (including the ECU ground wire). Also check that the Eprom internal to the ECU is properly seated.

Also, check if your tach drops to zero when the pump cuts out. The ECU shuts off the pump if the crank rotation sensor signals that the engine has shut off. If the gap to the sensor is incorrect/gets too big (say as the engine heats up) or if the connection to the sensor is problematic the pump shuts off. A tach dropping to zero tells you that the ECU is not getting a crankshaft rotation signal.
 

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Discussion Starter · #3 ·
Thanks. I have checked the ground wire and eprom. I also reseated the ECU plug but haven't taken it completely out yet to check wire connections. The bike has never shut down once it's started. I have the Haynes wire diagram and I was wrong about what the relays do. Relay 1 provides a signal to the ECU but I'm not sure what for. Relay 2 handles fuel pump, coils, and injectors. I'd like to get my hands on a schematic of the ECU. Anyway...I'll keep hammering away at it. Maybe there is a micro relay on that ECU board. Thanks again.
 

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Discussion Starter · #4 ·
The plot thickens

Ok...so I disconnected the ECU plug and jumpered to ground the two pins that service -vdc to relays 1 and 2. Both worked as expected. After peering into the ECU compartment it looks as though they may be switching those outputs with capacitors. Can't be sure though without an ECU schematic. Anyhow...there is a test socket off of the ECU with three wires so I hooked everything back up turned the key on and started testing those points with a test light just to see what signals there might be. Lo and behold! When I touched the last pin the fuel pump started and has worked everytime since. In the end it appears the ECU has become unreliable. Hope this helps anyone else dealing with the same problem.
 

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Ok...so I disconnected the ECU plug and jumpered to ground the two pins that service -vdc to relays 1 and 2. Both worked as expected. After peering into the ECU compartment it looks as though they may be switching those outputs with capacitors. Can't be sure though without an ECU schematic. Anyhow...there is a test socket off of the ECU with three wires so I hooked everything back up turned the key on and started testing those points with a test light just to see what signals there might be. Lo and behold! When I touched the last pin the fuel pump started and has worked everytime since. In the end it appears the ECU has become unreliable. Hope this helps anyone else dealing with the same problem.
Gotham Cycles - The Ducati Parts Specialist
 
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