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Dominick
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 1999 merc cruiser 454 cubic inch. the boat performs

Customer Question

I have 1999 merc cruiser 454 cubic inch. the boat performs on step perfectly for say 10 12 minutes at 3100 rpms and then starts gurgling and loses power. I pull back throttle idle a little bit and then back on step for say 6 8 minutes and the same thing. it appears to me ot be gas related... we put new fuel pump on last fall and i put new fuel filter on yesterday same thing in lack of power after running perfectly for say 10 12 minutes at 3100 rpms Fis advise?
Submitted: 2 years ago.
Category: Boat
Expert:  Tan replied 2 years ago.

Hi my name isXXXXX will assist you.

.

This sounds like you might have a fuel restriction in the boat side fuel system. Here is a test you can perform to verify this is an issue or not. This will tell you if you have a engine related issue or a fuel supply issue.

.

Get a vacuum gauge, a brass tee 3/8 and some fuel hose. Tee in the brass tee on the suction side of the fuel pump (location A,B or C) and connect the vacuum gauge. Run the boat all rpms or till the engine starts to loose power and watching the vacuum gauge. The gauge should never exceed 2" of vacuum, if it does you have a restriction in the boat side fuel system.

.

Check for debris in the fuel tank clogging up the screen on the end of the pick up tube, check the anti siphon valve at the top of the fuel tank, inspect all fuel lines for deterioration.graphic

Customer: replied 2 years ago.
I WILL TRY THIS ON THURSDAY AS THAT IS FIRST DAY I CAN GET TO BOAT FOR TESTING. IF IT IS ENGINE SIDE WHAT IS POTENTIAL ISSUE...ISSUES???
Expert:  Tan replied 2 years ago.

Is this engine EFI or MPI? Could I get the engine serial number please?

Customer: replied 2 years ago.
BOAT AND PAPERWORK DOWN AT MARINA WIL SUPPLY TO YOU ON THURSDAY.
HOW DO WE COMMUNICATE ONCE I SIGN OFF?
Expert:  Tan replied 2 years ago.
You can add this link to your favorites. Just post back to your email. Save this link. If you loose me you can just repost and put my name in the question or request me like you did before. I will get your reply.
Customer: replied 2 years ago.

Tan


Still have same issue. Since I tried your solution I took boat in and had it put through complete diagnostics via computer module plug in. Every thing checked out fine and he just said bad gas. I put additive in it (seafoam) and tried again this week. It is running longer before it starts to miss and sputter. Last night we came across lake at 3200 rpm for 20 minutes then it started sputtering so I throttled back to 2600 and it ran smooth but of course it is not planned off so crappy ride back to port. What I have put new spark plug wires on and new distributor cap....could it be coil heating up and shorting out?

Expert:  Tan replied 2 years ago.
How many inches of vacuum were you getting when the engine started acting up. If the coil was the issue it wouldn't make difference what rpms you were running. So when you back off throttle it would still miss. I still believe you have a fuel starvation issue.

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Dominick
Dominick
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25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified