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1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
- grizer
- Scurvy Dog
- Posts: 35
- Joined: August 7th, 2018, 2:48 pm
- Vessel Info: 1998 Carver 350 Mariner
- Location: Port Clinton, OH
Re: 1998 350 Mariner 5.0 Merc 3000RPM WOT
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- First Mate
- Posts: 123
- Joined: September 25th, 2018, 8:36 am
- Vessel Info: 2002 Carver 410 Sport Sedan
- Location: Peterborough, Ontario, Canada
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Re: 1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
- grizer
- Scurvy Dog
- Posts: 35
- Joined: August 7th, 2018, 2:48 pm
- Vessel Info: 1998 Carver 350 Mariner
- Location: Port Clinton, OH
Re: 1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
- grizer
- Scurvy Dog
- Posts: 35
- Joined: August 7th, 2018, 2:48 pm
- Vessel Info: 1998 Carver 350 Mariner
- Location: Port Clinton, OH
Re: 1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
- km1125
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Re: 1998 350 Mariner 5.0 Merc 3000RPM WOT
- bud37
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Re: 1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
I really think you may have to bite the bullet here and have someone hook up a laptop to the engines and take it out for a run to get a recorded log to inspect all the engine parameters while under Load.....that cannot be duplicated running at the dock, that just leaves you open to damage.
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- CYO Supporter
- Posts: 2291
- Joined: March 28th, 2016, 10:52 pm
- Vessel Info: 1998 Carver 355
Suspicious Fishes !
2022 Kawasaki 310X - Location: upper chesapeake bay
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Re: 1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
Do you keep the boat in the water all year? If so, maybe you have a nice carpet growth on the bottom. You would be amazed at how that can and will slow you down.
I had a 29 crownline with twin 5.7 mags and B3 drives, a 54mph boat, was unable to use it for two months one year due to work travel, it wouldn't get above 30mph. Stopped at a shallow beach area and found 3" shag carpet on the bottom. Scraped the worst, got 40mph, after an hour cruise 50+.
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- CYO Supporter
- Posts: 2291
- Joined: March 28th, 2016, 10:52 pm
- Vessel Info: 1998 Carver 355
Suspicious Fishes !
2022 Kawasaki 310X - Location: upper chesapeake bay
- Has thanked: 314 times
- Been thanked: 583 times
Re: 1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
Then there are the injectors. But if you don't have the proper pressure to them, I wouldn't change them until you do.
Unless you have the mercury smart craft system, which I doubt on a '98, the sync will not restrict the rpms, only monitor them. Without the smart craft, there is no relation to the fuel pumps, throttles etc. The ecm, turns on the fuel pump (again, its on or off, not variable speed or variable voltage) and controls the fuel injectors based on the throttle position.
- grizer
- Scurvy Dog
- Posts: 35
- Joined: August 7th, 2018, 2:48 pm
- Vessel Info: 1998 Carver 350 Mariner
- Location: Port Clinton, OH
Re: 1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
- km1125
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Re: 1998 350 Mariner Mercruise 350 Magnum 2800 RPM WOT issue
On an MPI engine, usually if there's a vacuum line on the fuel pressure regulator the fuel pressure will be lower when the engine is under low load (like idle or higher RPMs in neutral) and only let it go to full pressure when there is no or low manifold vacuum. The vacuum line "tells" the pressure regulator to lower the pressure. As more load is placed on the engine and vacuum goes from ~15 to ~5 (or ~0), then the pressure regulator increases the pressure. You can think about it like the injector has to "push" fuel against a pressure instead of the fuel being "sucked" out of the injector with some vacuum. This is so the injectors see the same delta in pressure from the inside (the fuel pressure) to the intake manifold, so every time they squirt fuel for "x" milliseconds they know exactly how much fuel was squirted. Even though YOU see the pressure changing when you measure it, the idea is that the fuel injectors DON'T see a change in pressure. You're measuring fuel pressure relative to air pressure (14.7PSI absolute) but the fuel injector "sees" the delta between the fuel rail pressure and the manifold pressure, which can change from nearly 0 absolute (theoretically) to 14.7 absolute. At idle, the manifold pressure is about 7.5 PSI absolute, so if your target fuel pressure is 40PSI, then at idle you'd only see 32.5 PSI, and these are the corresponding differences you should see when you yank the vacuum line off the pressure regulator while running at idle.
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