MERCRUISER 4.3 MPI fuel pump failure

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tomiro

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Hello there! Our mercruiser 4.3 MPI (2003 / 130 hrs) recently gave up working. Had been running wonderfully when I decided to stop, relax a bit.<br />When I decided to restart the engine:<br />* Start very shortly at 200 rpm then stop<br />* Restarting again rotation ok but no start.<br />* Notice change in sound of the fuel electric pump<br /><br />Mechanic told me he checked: <br />* Water in filter (little) <br />* fuel filter seems ok <br />* pump Volt Amp feeding ok<br />* Pump pressure (half the recommended values)<br /><br />I am not sure wether there is a device close to the pump to control fuel pressure, if not this means pump is gone? I guess! and also any comments what can cause it (I read somebody has changed 3 pumps in 2 years on a 5.0 MPI) debris<br />blocking filters ??? etc<br /><br />* There was always enough fuel (no dry run)<br /><br />I'd like to find out so to minimise chances of reoccurance.<br /><br />Many thanks in advance for any comments.<br />tommy
 
Silvertip

Silvertip

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Re: MERCRUISER 4.3 MPI fuel pump failure

If the fuel pressure regulator has a vacuum line on it, remove the line and shake it. If a small amount of fuel comes out, the pressure regulator has a bad diaphram. If no fuel comes out, make sure you have 12V on the pump when its running. If pressure is still low with 12V on the pump, the pump is probably bad or there is a restriction on the suction side.
 
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tomiro

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Re: MERCRUISER 4.3 MPI fuel pump failure

Many thanks to Lieutenant for the quick reply. I'm sending comments to mechanic.<br /><br />cheers<br />tommy
 
Bondo

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Re: MERCRUISER 4.3 MPI fuel pump failure

* Water in filter (little) <br />* fuel filter seems ok <br />
Click to expand...
A Filter with Water in it,... Isn't OK.....<br /><br />Go with Upinsmoke's diagnosis plan,........<br /><br />And,.... Definitely a Thorough Check of Everything Up-Stream of the Pump is in order.........<br />Tank pick-up,.. Venting,.. Check-valve,.. Lines,... Everything..........
 
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Capt Ken

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Re: MERCRUISER 4.3 MPI fuel pump failure

Did the mechanic have the proper equiptment to check this engine? He should have had a DDT to plug in and thus be able to get a reading on everything that might be happening. This would have given him fuel pressures. If not they you wind up changing parts and hoping its the correct ones.
 
Don S

Don S

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Re: MERCRUISER 4.3 MPI fuel pump failure

The DDT doesn't give you fuel pressures, but a fuel pressure gauge will, and he did mention that the fuel pressure was only half of what it should be.<br />You need a fuel pressure gauge, and some shutoff valves with the special fittings hooked up to the engine. Then there are special procedures in manual #36 for testing the fuel system, and isolating rather the problem is injectors, regulator, pump, or whatever.<br />All the special shutoff valve hoses, disconnect tools, and gauges are readily available at automotive stores, and are not Mercruiser only special tools, but they are tools needed to check the system out properly.
 
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tomiro

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Re: MERCRUISER 4.3 MPI fuel pump failure

Hi All, thanks again<br /><br />Mechanic used other fuel pump and engine run but at minimum is no working propely. He is going to clean injectors.....<br /><br />How could water pass filter separator ? Hope injector pump is not damaged....<br /><br />I'll pass above comments and check on the way is tested the engine.
 
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tomiro

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Re: MERCRUISER 4.3 MPI fuel pump failure

Hi All<br /><br />I read somewhere somebody with a similar MPI 5 Liter changed 3 fuel pumps in 2 years (or the other way round) <br /><br />Is there a design problem ? Perhaps in some installation wrong tubing size/length etc creates too much pressure drop ? <br /><br />see you<br />tommy
 
Bondo

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Re: MERCRUISER 4.3 MPI fuel pump failure

I'd sooner think there might be a Restriction,.. Upstream of the Fuel Pump,..........<br /><br />Tank Vent,....<br />Tank Outlet,...<br />Check-Valve,....<br />Collapsed Fuel Line,...<br />Plugged Fuel Filter,...<br />Etc.Etc.,....
 
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jaybirdtx

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Re: MERCRUISER 4.3 MPI fuel pump failure

4.3L fuel pumps are a common headache. Merc has a service bulletin out on these....finally!
 
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tomiro

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Re: MERCRUISER 4.3 MPI fuel pump failure

Hi <br />good idea these checks especially the tank vent...<br /><br />Add to checklist. <br /><br />Other questions I have: <br /><br />Mechanic seemed to have quickly disassembled and cleaned injectors. We had a look at engine but while there are clear marks of handling on the pump, we can't see any sign of disassembling the injectors (I assume are the ones with a wire, sensor ? , coming out of them, spark plugs region..) I ought to buy the manual...<br />So. Is it possible to remove injectors leaving everything, paint and all, intact ? <br /><br />How do they normally clean injectors, without damage ? <br /><br />If it is a design problem, could we add a temperature probe on the pump or better insert a shunt resistor to measure current going in the pump. If there is a block up stream the current absorbed should go up warning to stop. (making sure the lot stays...spark...proof...)<br /><br />thanks <br />tommy
 
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Capt Ken

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Re: MERCRUISER 4.3 MPI fuel pump failure

Don, upgrade your module for the DDT, mine gives fuel pressure. Use the one for the SmartCraft.
 
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newport dave

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Re: MERCRUISER 4.3 MPI fuel pump failure

Capt,<br />I have to agree with Don, the DDT does not display fuel pressure data.<br /><br />Tommy,<br />Try another mechanic. Your guy seems not to have the equipment, service literature, or knowledge to diagnose a computer controlled engine.<br /><br />Dave
 
Don S

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Re: MERCRUISER 4.3 MPI fuel pump failure

Do have the Smartcraft cartrige. Still no fuel pump pressure.<br />There is info for the relay working or not. Look at manual #36 for testing the fuel pump pressure along with the rest of the tests for the fuel system.<br /><br />Here is what the DDT will do with the Smartcraft cartridge installed.<br /><br />
DDT%20operations.png
 
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Capt Ken

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Re: MERCRUISER 4.3 MPI fuel pump failure

Dang, could have sworn the last engine I checked showed the fuel pressure, probably confused with the Yamaha YDS.
 
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jfrenzel

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Re: MERCRUISER 4.3 MPI fuel pump failure

We have a 2003 4.3 MPI and just started having trouble this week. Engine tries to start but acts starved for fuel when warm after running. Temp never over 175 fuel filter replace twice, have been using premium fuel no ethonal. Boat runs great when first started no lost of power, after cooling down will start and run great again. Tried new plugs, loosen fuel cap. Battery is seven years old but tested fine could it be to weak to supply the sytem when warm? Turns over fine fuel pump primes and shuts off when key in turn. Any thoughts or to the dealership they are three to four weeks out. Thanks Jon
 
Don S

Don S

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Re: MERCRUISER 4.3 MPI fuel pump failure

Welcome aboard Jon
Best to start a new thread with your question, and not drag up someone elses 5 year old thread and post at the end. Your question will be misses completely by many, or you may receive answers for the original posters question.
Very confusing.
 
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