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Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3981
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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The electric fuel pump stops working about 5 seconds after

Customer Question

The electric fuel pump stops working about 5 seconds after is starts
JA: 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. Tell me a bit more about what's going on so the Marine Mechanic can help you best.
Customer: My electric fuel pump stops running about 5 seconds after it starts
JA: Is there anything else the Marine Mechanic should be aware of?
Customer: We changed out the ignition prior to this problem
Submitted: 5 months ago.
Category: Boat
Expert:  Jason replied 5 months ago.

Hello my name is***** read what you wrote but do not see any kind of model information. What are you working on?

Expert:  Jason replied 5 months ago.

Are you here?

Customer: replied 5 months ago.
Mercury 40 efi
Expert:  Jason replied 5 months ago.

Mercury engines are cataloged by serial number. Can I get the serial number on yours so I can run it and see exactly which version of the 40 you have.

Customer: replied 5 months ago.
Expert:  Jason replied 5 months ago.

Got it. Now are you loosing power to the pump or are you loosing ground to the pump?

Customer: replied 5 months ago.
Neither, it primes for about 5 to 10 seconds and the stops, if I power cycle the key fast it turns the fuel pump on again for 5 seconds or so.
Customer: replied 5 months ago.
Thank you
Expert:  Charles replied 5 months ago.

Hello, my name is***** will assist you from here.

The ECU on this engine will allow the pump to run for only 5-10 seconds at key up. The pump then times out until a crank signal is recieved from the CPS to the ECU. So what you are seeing is normal.

Is there an issue with the engine other than this?

Customer: replied 5 months ago.
What's keeps the high pressure pump running after the engine starts? The beige dies after the fuel pump turns off.
Expert:  Charles replied 5 months ago.

The ECU controls the ground signal to the pump telling it when to run or not.

When the engine stalls, is it actually losing fuel pressure, as checked on a gauge, or losing spark?

Customer: replied 5 months ago.
It's losing fuel pressure
Expert:  Charles replied 5 months ago.

Ok, look at the left side of the valve cover, there are 3 relays there. One has a blue wire, one has a green wire, and the other should have a yellow wire to it. Take one of the other two and swap it with the one with the yellow wire to it. This is the main power relay. If the engine will not run, you will need to replace that relay.