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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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by AlboranC » 25 Apr 2020, 09:31

Well I finally got round to fixing this and the fuel pump was indeed dead. The fuel pump on the EFI is buried underneath the port side forward engine mount - it might be possible to remove it with the engine in the boat, but I opted to remove the engine and do various other jobs on it while it was out, including a new starter motor. The engine now starts and runs.

If this happens to anyone else and they find this thread in the future, I would recommend removing the port side manifold and riser, unbolting the cool fuel unit from the port engine mount, disconnect the fuel pipes at the fuel filter and the throttle body, disconnect the cool fuel water hose at the power steering cooler and at the thermostat, disconnect the vacuum tube that goes to the throttle body, disconnect the electrical connector at the pump (if you can't reach it you will have to cut it off and rewire it) and then try pulling the whole cool fuel unit out from the front of the engine using the water hose. You will have to the feed the other hoses and tubes through the maze at the back of the engine while you pull it out the front. I think this can be done and would save pulling the whole engine out.

Thanks to everyone who commented.

Oh, and god help anyone who needs to change their starter motor mid season - you might be better off sinking the boat and claiming on the insurance instead.
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by shibbs » 27 Apr 2020, 11:15

Glad you got it sorted, what a pain having to take the engine out but saying that, by the sounds of it definitely made the job easier.
Fingers crossed you can get out soon to test it out.
Stu

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by shibbs » 27 Apr 2020, 11:17

Also, a really useful write up should anyone else ever have the same issue.
I find I solve a lot of problems by having a read through posts where others have been in the same bother before, both for car boat and bikes. Always useful to have people take the time to share the info. :geek:
Stu

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