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My 2012 Mercury 90 HP EFI outboard runs well but after

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My 2012 Mercury 90...

My 2012 Mercury 90 HP EFI outboard runs well but after sitting for an hour it restarts, idles rough, has no power and eventually dies. I found that when this occurs, fuel pressure has fallen off. Looking further into it, i found that when this occurs i can disconnect the fuel line at the fuel injector rail and have an assistant crank the engine while i observe the disconnected line. It is has little to no fuel squirting out at first but after 5-10 seconds, i see a steady flow. If i then hook the fuel back to the rail, it runs perfect until i stop and kill the engine for another hour or so. Upon restarting, the same issue. It appears that the fuel module has two pumps in it. One is a lift pump, or low pressure pump, that fills the module cavity with fuel. The other is the high pressure pump which sources fuel from the fuel module and sends it to the fuel rail. It seems that the module is draining when i turn off the engine and the high pressure pump has no fuel to source until the fuel rail module cavity is refilled

Mechanic's Assistant: Sometimes boat issues seem like they'll be really complicated, but end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Is there anything else the Marine Mechanic should be aware of?

It is a 2012 Excursion Pontoon with low hours. Only 75 hours. There are no signs of external fuel leakage

Submitted: 3 months ago.Category: Boat
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Answered in 6 minutes by:
4/2/2018
Marine Mechanic: Charles, Marine Mechanic replied 3 months ago
Charles
Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 4,755
Experience: US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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Hello, my name is***** will assist you.

Is there a primer bulb in the fuel line?

Is the fuel tank mounted above the engine?

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Customer reply replied 3 months ago
No primer bulb. Fuel tank is mounted below engine
Marine Mechanic: Charles, Marine Mechanic replied 3 months ago

Ok, the engine does not require one.

Have you already looked into the fuel hose from the engine to see if the center of it is coming apart? This would cause a fuel restriction.

When was the last time the fuel filters were replaced?

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Customer reply replied 3 months ago
I haven't replaced fuel filters. Lines do not appear to be clogged. Keep in mind that it runs perfect after disconnecting the line and cranking until seeing a steady fuel stream. It will run for hours, has full power, no hesitation at all until I kill it and sit for a while. Would it be able to run like this if it had a clogged line or filter? Is there some kind of check valve incorporated in the fuel pump(s) or fuel filter(s) that prevent fuel from returning and draining the fuel pump module?
Marine Mechanic: Charles, Marine Mechanic replied 3 months ago

The module is mounted above the center line on the engine, it will not drain back. With the engine running batter after you disconnect the fuel line, this tells me that somehow the engine is getting too much fuel to it, and that is causing the float to not trigger the lift pump.

When you remove the fuel line from the engine, how much fuel comes out of that line?

When opening the gas cap, is there pressure in the tank?

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Customer reply replied 3 months ago
When I remove the fuel line from the engine, little to no fuel comes out until I crank it for 5 seconds or so.
Marine Mechanic: Charles, Marine Mechanic replied 3 months ago

Cranking the engine with the fuel line disconnected cause fuel to come from the gas tank on the boat?

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Marine Mechanic: Charles, Marine Mechanic replied 3 months ago

Follow hose 8 back to where it connects to, past part 6. Remove the hose from that fitting. See if you get any fuel from this hose. While it is disconnected, open the green cap on hose 8 and then press in on the schreder valve, see if any fuel then comes from this hose.

http://www.boats.net/parts/search/Merc2/Mercury/115%20EFI%20%284-STROKE%29/1B366823%20%26%20Up/Integrated%20Air%20Fuel%20Module/parts.html

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