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Fuel pump failed on my Mercruiser 4.3EFI

by AlboranC » 16 Sep 2019, 08:31

Can anyone tell me how the fuel system on a Mercruiser 4.3EFI 2001 vintage works? My boat won't start - there's fuel in the tank, spark at the spark plugs, but no sound of the fuel pump running and no fuel at the injectors. All the fuses are good and I also tried swapping the two relays over. If I could get to the fuel pump I would test for voltage at the pump, but it is buried somewhere under the port side of the engine.

The fuel line from the tank comes in on the starboard side and runs to the water separator filter which is buried under the starboard side of the engine. I was wondering if anyone can describe how the filter/separator is connected to the fuel pump, where the fuel lines run (I assume there is a pressure regulator in there as well somewhere). It looks like there are three connections to the fuel filter, which I don't understand, so if anyone knows what that is about that would be handy.

Any explanations, tips or general pointers would be useful before I dismantle half the engine to get at the fuel pump.
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by Ianfs » 16 Sep 2019, 13:23

Hi AlboranC

Welcome to the forum.

This is not going to be a great help but suffice to say one of the chaps in in the same boatyard as me had an issue with his electric pump a couple of years ago. As no doubt you know, Mercruiser changed them from mechanical to electric when they went to MPI, this was to get the pressure to the injectors. Neighbour opposite has a Mercury 200 which has 2 pumps one of which produces about 80-90psi. He was only getting about 20 psi so had to change it out.

I helped him out whilst I was there. From what I remember, it was a real bu**er to get to. After faffing with phone camera's, lead lights and mirrors we saw that the fuel line from the separator goes to the fuel regulator which sits on the fuel cooler. The fuel pump unscrewed from the cooler via a 90 ° fitting. In the end with our limited knowledge of the geography of all the fittings, we both decided that it was best to take off the exhaust manifold. I'm afraid the rest is a bit of a blur, so maybe not much help.
Oh one more thing if you do decide to replace it make sure you get the right one, I think there are about 3 choices.
Good luck.
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by AlboranC » 16 Sep 2019, 15:01

Thanks Ianfs, that is helpful.

I've just had another look at it and I think I will start by taking the riser off first to get a better look and then see if it looks like removing the manifold will help. There is very little clearance between the side of the cool fuel unit and the bulkhead - if this was a car I'd be cutting a hole in it to get access, lol.
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by betty boop » 18 Sep 2019, 20:47

can you not take the hatch off? on my 4.3mpi i had the engine hatch off recent and it made life so much easier so did some other jobs at the same time, no idea on the problem but Id recommend a search on iboat.com they had loads of 4.3 fuel probelms last I looked and most things have happened over there before
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by AlboranC » 20 Sep 2019, 14:22

The hatch is open all the way and there are no other access panels. If it was a car I would have cut a hole in it by now to get at the pump, but I don't fancy doing that on a boat. :mrgreen:
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by Ianfs » 21 Sep 2019, 10:40

Agree with betty, I don't wish to send you away to another forum but yes iBoats.com are a fountain of knowledge and have a few Merc engineers on it. As a US forum there are tens of housands of sportsboats so someone can help.
Out of interest, which boat is it in?
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by argonaut » 05 Oct 2019, 22:23

What about putting 12V direct onto pump ... if it works then it’s the wiring if not it’s the pump.
I have Mercruiser 4.3 MPI. Pump is fully accessible, assume your motor is different.
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