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Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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I have a 50 hp efi 4 stroke Mercury that will not run above

Customer Question

I have a 50 hp efi 4 stroke Mercury that will not run above 2200 rpm. I have purged and cleaned the fuel tank and lines and cleaned/replaced the fuel filters (primary and secondary). I also replaced the hi-pressure pump inlet screen and cleaned the vaper separator system. I checked the fuel pressure and at 2000 rpm it was 45 psi. I also changed the spark plugs but nothing has helped. Any help would be much appreciated.
Submitted: 4 months ago.
Category: Boat
Expert:  Jason replied 4 months ago.

Hi Charles, my name is Jason.

Has engine compression and spark output been checked yet? What is the serial number on the engine? What is the history on this engine, have you ever personally seen it make full power under a load?

Customer: replied 4 months ago.
The engine is s/n 1c083458. I think it was new in about 2004. It only has 1 or 2 hundred hours on it. Did not take a compression check but the motor is solid and all 4 cylinders are firing. One big omission I made in my first report was that the motor did go under water 2 weeks ago. I raised it and drained and flushed everything several times (Sorry for the omission). Yes I have seen it under full power many times up to 2 weeks ago. BTW I ran each fuel injector and they are all spraying about the same pattern and amount at idle. Not sure what this proves except that everything appears normal.
Expert:  Jason replied 4 months ago.

Hi Charles. The engine needs to be compression tested first. After that the spark needs to be checked under a load. The easiest way to do this is to run the engine with the cover off. Hook up a timing light to each plug wire, and see if the light shows a flash with the boat going as fast as it will go. Is this something you can do?

Customer: replied 4 months ago.
I don't have a compression tester, but mechanically I can't think of any reason why the compression would go bad just because it was under water for a very brief period. It was fine up to then. Now it only runs smooth up to 2200 and it idles smooth. As for the spark test, I gave away my timing light last year thinking it wasn't going to need it again and a friend needed one. Is there some other way to test this? Also even though the injectors seem to spray evenly and in the same amounts is there anyway to tell if they are restricted?
Expert:  Jason replied 4 months ago.

Sounds like you don't have the tools required to do basic troubleshooting. Fixing this engine is not something we are going to be able to accomplish together. Aside from those injectors, which need to go into a flow tester to see if they are flowing the correct amount of CC's per minute, did you have any questions for me?

Customer: replied 4 months ago.
I guess not. Thanks.
Expert:  Jason replied 4 months ago.

Okay good luck

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