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Old 04-02-2009, 06:54 PM
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Default Mercruiser 454 MPI fuel pump questions

Guys, was trying to help a buddy with his boat this afternoon. Just want a reality check.

He has a pair of ~2001 Mercruiser 454 EFI/MPI engines.

One engine quit on him a while back and he's just now gotten around to fixing. He had some electrical issues, and somewhere along the way his starter went bad. They replaced the starter, and now the engine cranks fine, gets spark, but won't run.

I noticed that the "good" engine, as soon as you turn the key on, the fuel pump loudly runs for about 2 seconds - just like most cars. On the "bad" engine, no such luck. I swapped what I believe were the fuel pump relays between the two engines, with no change in behavior. I could not find a fuse or anything like that, but did find a 50A circuit breaker on the top of the engine that was fine.

It was getting dark and a little cramped but I'm pretty sure I unplugged the fuel pump from the harness and verified that 12v was getting to the harness. So I am assuming the pump is shot. This is a little surprising because he just had it replaced it a few months ago.

Three questions:

- Is there anything that would stop the fuel pump from pressurizing the system at key on? IE any pressure switches to check, etc?

- The pump itself seems to be in some sort of weird assembly that cooling water runs through? I guess it's a heat exchanger? Is this a single unit or can the electric pump alone be replaced? I was too contorted to really get a look at it... how tough a job will this be?

- Is this that common a failure?
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Old 04-03-2009, 07:42 AM
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I had a similiar issue with my 350's when one motor was changed to a new 310 crate motor with the electric fuel pump. The other motor was a 260 hp with a mechanical fuel pump. The new motor would run of a auxilary tank fine but it wouldn't run off any of the boat tanks. After searching and checking the fuel pumps the same as you have it ended up being a air leak at the fuel fittings. Once I fixed the air leak it starts like a champ. I don't know if any of the fuel lines were removed or anything like that but it sounds like its getting air in the system.
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Old 04-03-2009, 07:50 AM
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- Is there anything that would stop the fuel pump from pressurizing the system at key on? IE any pressure switches to check, etc?
Fuel pump fuse? Burned out motor? Bad ground? You have confirmed that it is getting power to the pump with the key in RUN?

- The pump itself seems to be in some sort of weird assembly that cooling water runs through? I guess it's a heat exchanger? Is this a single unit or can the electric pump alone be replaced? I was too contorted to really get a look at it... how tough a job will this be?
You can replace just the pump. Job is a PITA. Cool Fuel thing helps reduce vapor lock in the line.

- Is this that common a failure?
Having a spare fuel pump on board is always good policy. Obviously had this happened at sea one could get home on one lump, but like a twin engine airplane, it gives you a good feeling in your heart to have all engines running smoothly.
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Old 04-03-2009, 12:49 PM
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Sounds like a MERCRUISER COOL-FUEL assembly. The outer cover pops off to expose the fuel pump and cooler inside. If the engine has sat for very long, then yes a piece of sludge or something could have lodged itself in there when you turned it on. The pump is replaceable seperatley, but they are not cheap. Verify you have power and ground to the pump by backprobing the connector at key on first. You might also want to try and run direct power to the pump to see if it runs. The fuse will be in the black box mounted on the port exhaust riser if this is a I/O or straight inboard, if V drive it will be on the starboard riser. Also check the grounds on the back of the block. There should be a stud on one of the bellhousing bolts that has 2 ground wires on it I believe. One will be your fuel pump.
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