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Boat: 2010 Frenzy H200
Motor: Mercruiser 4.3L MPI / Alpha 1 leg
SN: 1A611503

I have been having an ongoing problem with electric fuel pump that makes a whirring/buzzing noise.

Took the boat to an authorised Mercruiser repairer who charged like a wounded bull to pull out the engine and replace the electric fuel pump. Problem returned after first outing and to help make a long story short... there's no way I am going back to that dealer!!

So I have taken a few steps to try and work out what the underlying problem may be as I find it hard to believe that 2 electric fuel pumps could fail (first one failed after 21 hours use).

I bought an fuel pressure gauge and hooked it up to the schraeder valve on the fuel rail and here are the results:

Test 1:
Key on pressure - 32psi
Engine idle pressure - 36psi
Engine at 1500 rpm - 32psi

Test 2:
Key on/off 3 times - 42psi when pump is on and priming then when pump stops psi drops back to 32psi.
Engine idle pressure - 36psi
Removed vacuum hose - no difference to pressure.

I believe the pressure should be 43psi but I'm not sure if I tested it properly ie should 43psi be reached at pump prime? at idle? at WOT? or other?

Next test I want to do is a vacuum gauge test but the H200 engine bay makes servicing the fuel pump very difficult due to poor access. The vacuum test should be performed by inserting the gauge at the fuel inlet side of the cool fuel module but there's no way for me to get in there. Can I expect the same vacuum results if I insert the gauge between the fuel tank and the separating fuel filter??

Any advice on above would be very welcomed!!!

Ok, first. Did they just change the pump or also the regulator? From what I see, there is a pump and cooler kit, but does not say if the regulator is in that.

Second, Did they actually change the fuel filter? - I don't trust any shops anymore for cars or boats, including dealers.

Third, The hoses that feed into the system both from the tank and then the two, one to the pump, and one to the regulator return from the fuel filter. Sometimes you can get a hose collapse on the inside under pressure.

Fourth, The screen at the end of the hose in the tank.

Do you have a book? If not, get a book first and formost.

It sounds like your buzzing is one of two things. Either the regulator is sticking, or air is getting into the system.

_________________
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Just the pump was changed.

Before the service, I changed the fuel separating filter (no water was present) and since the service also pulled out the hose tank and checked the anti syphon valve... both were fine.

I'll take your advice and check the hoses again for any kinks or collapse. Next job is the vacuum test to see if there's an air leak. Just waiting on the gauge to arrive in the post.

Still wanting to confirm my tests that I outlined in the initial post. I do have some service manuals (#36 and #40). #36 describes the tests for pressure and vacuum but there's no specific detail ie what the pressure should be (I'm pretty sure it should be 43psi) and no detail on when that pressure should be attained ie at idle, at WOT etc.

Thanks for your help.

Typically with the engine on, Your fuel pressure should read anywhere between 38-41 psi, with spikes up to 43. Since the fuel pressure did not go up to 42-43 when you removed the vacuum hose, this is a sign that the regulator is not doing it's job. You cycling the ignition key and getting 43 psi tells you the pump is building the needed pressure. To confirm the pump is good, block the fuel return line using a special shut off valve tool then cycle the ignition key to build up to 60 PSI, Also in your case, blocking the fuel return line should help hold more pressure (38-43 not 32) after cycling the ignition key.

91-805918A1, Merc Fuel Shut Off Tool
861126A1, REGULATOR KIT, (43 PSI)