I have a 2015 Monterey 268SS with a 8.2. 250 hours


Two years ago I noticed that at high RPM the motor felt like it was running out of fuel and wouldn't go over 3800-4000 rpm. WOT is 4600-5000 which I used to achieve. I also had a O2 sensor fault.


I took it to a local dealer and they changed my plugs and the O2 sensors. Got back out on the lake last year and it was doing the same. I took it to a local mechanic, he took the catalytic converters out and added an aftermarket computer to fool the CPU. He also changed plugs, crank sensor, cam sensor, front O2 sensors, and the throttle position sensor. The codes were still there and the boat eventually wouldn't go over 1500 RPM.


I took it to another dealer who told me it was the fuel system. He got Mercruiser to warrant the parts, I paid the labor and he changed the pumps, lines, and injectors. I took it out last week and it immediately showed codes flashing but it ran good for 15 minutes then I steadily lost RPM, down to 4000 max or so in 30 minutes. I took it back to the last guy and he wanted to charge me $8000 to install new catalytic converters (I still have the old ones). I know this isn't going to fix the issue. Even though he worked on it last year he insists it is illegal for him to work on it as it is not EPA compliant.


I need to get the codes to go away then I need to figure out the loss in RPM. Is it possible this is a computer issue? In the last 2+ years I've had this in the shop for 10 months. Any suggestions would be appreciated.

What are the codes being displayed?

Have you looked at the fuel press when running good VS running bad?

To the group: Could this be one of those years where paint was flaking off internally and contaminating fuel sys?

Computer issue? possible but doubt it. To me if the motors running right down low and only acting up when trying to get to full rpm and nothing else has changed like a bent prop blade etc....then i would tend to think its either fuel related or compression.... i'd start with a basic compression test....then a leak down test...if those come out showing nothings wrong then i would move to get the injectors cleaned/flow tested and matched. 250hrs is nothing overall but then again fuel can be who knows how clean at some of these stations on the water....oh and make sure your fuel is good too.......all this is assuming the fuel/water filter is clean and new too....
Engine only needs 3 things to run...spark fuel and compression.....

Could be.... that was from 05-17 from what i remember...but hopefully that would have been seen if the fuel system was gone through by that last mechanic....

An additional thought… look to make sure there isn’t another filter sitting somewhere that you’re unaware of. A friend had a similar situation and and found that the boat had two filters, one of which was tucked up under stuff where it couldn’t be seen. He removed that filter from the system and never had a problem again.

Also consider the anti-siphon valve at top of fuel tank. Could be partially opening. New fuel system maybe overcame it for a bit.
‘My guess is it will be one thing that these mechanics have not yet found. Sounds fuel related.

I agree with others. Change fuel and look for another filter. I’m betting you have an inline filter. I’m also betting betting your fuel tank has varnish in it from gas sitting to long.

this or a collapsing fuel line. I have chased that many times. get a jug to run it off of and run new fuel lines to the connection at the engine and see if the problem goes away. if so then it is a fuel hose or anti siphon valve

What where the codes flashing when it ran good for 15 minutes ?

It was one of those years. They replaced the fuel system last year but still having the same issues.