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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 14166
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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I have a 5.7 350 magnum when I turn key over fuel pump kicks

Customer Question

I have a 5.7 350 magnum when I turn key over fuel pump kicks on and it starts . Pull out on water drive 300 yards and it dies and won't start back up unless I unplug a plug into the computer then fuel pump kicks back on and then will run fine all the temperature gauges look normal and the oil gauge . Looking for answers
Submitted: 4 months ago.
Category: Boat
Expert:  Jason replied 4 months ago.

Hi Dale, my name is Jason.

It sounds like there is a loose pin either in the ECM or in the harness where it plugs into the ECM. What we would do in the shop is swap the ECM with a known working one and try it. If that fixes it then it's a bad ECM, if not, then we would replace the harness. Does that make sense?

Customer: replied 4 months ago.
The Ecm is the silver plate that's the computer right
Expert:  Jason replied 4 months ago.


Customer: replied 4 months ago.
K I bought 2 new relays that I'm gonna change out today that are directly behind the Ecm do u know which one is for the fuel pump
Expert:  Jason replied 4 months ago.

Mercurys are cataloged by seral number, if you can get me the serial number on your engine I will be able to tell you.

Customer: replied 4 months ago.
K headed down to the boat now
Expert:  Jason replied 4 months ago.


Customer: replied 4 months ago.
Expert:  Jason replied 4 months ago.

If you look at the 2 relays, they are both to the left of the ECM. The main power relay is the one on the right, closer to the ECM. The one on the left, further away from the ECM, is the fuel pump relay.

Did you have any other questions on the issue?

Customer: replied 4 months ago.
Yea replaced both boat still doing it run 300 yards and die reset ecm and runs fine
Expert:  Jason replied 4 months ago.

Did you read my very first reply to you?

Customer: replied 4 months ago.
I will try that
Expert:  Jason replied 4 months ago.

I do want to make sure you are happy with my service before you go. If you had a further question on the issue by all means feel free to ask. If not, Just in case you do not understand the way the website works (and some folks do not). You do have to put forth a positive rating in order for it to credit me for helping you. When ratings are not done, the website simply keeps your deposit and they will not credit me. The ratings box is located at the top of the screen. To rate, you must select the star you wish and also confirm it. Please let me know if you run into any problems or errors when trying to do it. If you do have a problem, or if you can not see the ratings box which is at the top of the screen. Please reply back "I rate Jason's service _______" and fill in the blank.

Questions do not close out, so if you have to come back later on with follow up questions to the issue you still can even after doing a rating.

Thank you


Expert:  Jason replied 4 months ago.

Hi Dale,

It looks like you read my answer without replying back or leaving a rating for my service. Please keep in mind the website does charge you to speak with me. But they will hold your money and not credit me for helping you until you select a rating for me.

Thanks again,


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