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Four months ago I purchased a new fuel pump for my '04 749S. For the last 3 months I have not been able to ride due to health problems. Recently took the bike out.When I turn the key on, the pump primes and whines very loudly then the whining stops when the pump is primed. However, when I start the bike the pump whines again. Even while I am riding I can still hear a very high-pitched whine the entire time until I turn the bike off. The bike runs as it should. There is no hesitation or any fueling issues...just the noise. Should I replace the pump or live with the annoying sound? When I originally replaced the fuel pump I did not have the noise problem.
 

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You can hear it running over the bike's noise? OEM or aftermarket pump? Sometimes if the bike has been sitting for a long time, you can get a whine or whistle sound from the pump first time you turn the key to on. Normally cycling the key on then off a few times makes that go away. All the time though? Doesn't seem normal, but if it's running like it should, I guess... Are you sure all the internal plumbing is correct?

Also, you may know this, but the pump shutting off after a few seconds once the key has been turned on doesn't mean it's "primed". The ECU tells it to turn off after a short time and just assumes it's been on long enough to get fuel pressure up. The ECU has no way to know what the actually pressure is and does nothing to regulate it. Once the ECU detects an output from the CPS, meaning the engine is turning because you are hitting the starter button or actually running, it tells the pump to turn on again. It continues to run the pump until the ECU stops getting input from the CPS and/or power is removed from the system (key or kill switch to off). Fuel pressure is assumed to be correct by the ECU and regulated mechanically by the fuel pressure regulator.
 
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