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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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Wow, thanks 2001 Mercrusier 5.0LGoes minutes on 3/4

Customer Question

Wow, thanks 2001 Mercrusier 5.0L
Goes for ten minutes on 3/4 throttle then start spitting and chugging, slow down to idle or 1/8 throttle and it seems fine
Wow, thanks 2001 Mercrusier 5.0L
Goes for ten minutes on 3/4 throttle then start spitting and chugging, slow down to idle or 1/8 throttle and it seems fine
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.
Hello. This sounds like a fuel starvation issue as the engine runs ok at idle and in the beginning. Can you run the engine on an auxiliary fuel tank? This will eliminate a possible fuel restriction of the boat side fuel system. This is a process of elimination this test will tell us if the engine is the problem or the fuel supply is the issue.
Customer: replied 1 year ago.

I would need to buy a Aux. Tank and pipe it in so I guess so.

What about pick-up coil, Ign. Coil or possibly the

MERCRUISER THUNDERBOLT ECM/ECU IGNITION MODULE 861459-1

Expert:  Tan replied 1 year ago.
Those are not as likely as the fuel supply. The engine would quit running and it wouldn't only act up at higher rpms. These are not symptoms of an ignition issue. There is another test you can perform. This requires the use of a vacuum gauge some clear plastic hose and a brass tee. You will need to tee in the vacuum gauge at the water separator filter on the engine. Run the engine and monitor the vacuum gauge. The vacuum should never exceed 2" of vacuum at any rpms especially higher rpms. The engine chugging and slowing is fuel starvation then when you get to lower rpms the engine doesn't require as much fuel and will run. If it were ignition it wouldn't make any difference what rpms you are running at. Does this make sense?
Customer: replied 1 year ago.

yes in a way it makes sense.

I

Expert:  Tan replied 1 year ago.
Post back with your findings and we can come up with a fix.
Customer: replied 1 year ago.

I brought a spare tank with me but ran it on the main tank first until the symptom came up, shut down, hooked up the spare tank and took off, it ran fine for a couple of minutes then started to spit and sputter again. I also hooked up a semi clear line to see if I could watch the flow which I could and it seemed as if the fuel flow stopped then the spitting and sputtering occurred seconds after.

Expert:  Tan replied 1 year ago.
Fuel flow stopping is either a restriction or the fuel pump is quitting. Since you have eliminated a possible fuel restriction by using another tank that leaves the fuel pump.

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