Mercury 6.2L Loss of Planning Power/ Top End

[PremierPOWER]

I have a 2018 Monterey 335SY with twin Mercruiser 6.2L engines (300hp version). These are the newer Mercury in house version, not the older GM block style. The boat has been very slow to plane out, to the point I have to move people to the bow to help it. Its been doing this for awhile and I have not been able to figure it out.

- Props are perfect
- No alarms
- I just changed fuel filters, spark plugs, and PCV valves
- New gear lube
- New oil/ oil filter
- Cleaned intake screen
- Have also run fuel injector cleaner through several tanks of gas

What else could it be? The engines sound perfectly healthy, they are just lacking power to plane out and some on the top end as well. Engines have about 600 hours on them.

 

[itsathepete]

If you can get the serial numbers off the engines it will help those with access to factory manuals get the information they need to help you out. Also how long have you owned the boat and how long has the issue been going on. Have you added a significant amount of gear or other weight to the boat?

 

[itsathepete]

Also, I am assuming the boat stays in the water. Marine growth can foul the hull and block exhaust and cooling water in the drive. When was the last time the hull was cleaned and drives serviced?

 

[Rick Stephens]

600 hours is just getting broke in. Wonder if you are getting waterlogged somehow.

 

[PremierPOWER]

Ive owned the boat since new, in June 2018. It started doing this a bit last year when loaded down with people, but now I even notice it with just me. Boat is kept on a trailer, other than weekends when I am at different lakes.

one of the engine serial numbers is: 2A582450

I didn't have time to service the drives over the winter, so I had them serviced over the winter when I had the boat in Florida. I just recently changed the gear lube (2 weeks ago).

 

[Scott Danforth]

Compression test results?
Fuel pressure test results?

 

[PremierPOWER]

Compression test results?
Fuel pressure test results?

I plan to do those. Question, what is the best way on this engine to kill the fuel supply to crank it for a compression test? The boat doesn't have a kill switch, which is what I normally use for this.

 

[itsathepete]

Either use a remote starter switch with the key off or pull off or disconnect the fuel pump relay

 

[alldodge]

Don't worry about the fuel supply disconnect the coil