Help! 2006 lsv möbius... assault 325 won’t go over 3500 rpm

My 2006 möbius moomba won’t go over about 30 mph or around 3500 rpms....it will start surging almost like it is staving for fuel!
We have owned the boat for 7 months and it’s been a problem since we bought it....
Runs awesome up to that then won’t go any farther, I’ve tried to push it to see if I can get past that 30 mph point but it won’t.
So far I’ve changed fuel pump, inline fuel filter, tps sensor, map sensor, cleaned the throttle body. I even pulled the line from the tank and put it in a can of fresh gas and tan off of that but still does it....any help or ideas be awesome!

Not sure about the boat version of this motor....but it is a vortec GM based engine.

To me it sounds like the fuel pressure regulator is going out. It is vacuum controlled on cars/trucks and based on running conditions allows more fuel pressure to the fuel rail. This is why you are surging at higher RPM/Speed. You have plenty of fuel at low speed but when the boat needs to work the regulator won't allow it. I would have said fuel pump first but you mentioned that is new (could be dead out of the box).

There should be a test port on the injector rails. You need to put a gauge on that and run the engine. you should maintain 50psi or higher at all times. I bet around 30mph or 3500prm yours drops. Also, the injectors could just need a good clean job or 1 or more could be going bad also. If this test good, you have an ignition problem.

At that point, you need to check the ignition loop for issues. Crank position sensors, Cam position sensors, faulty coil, etc. The car version advances timing when at WOT, so it doesn't knock (premature fire). If you aren't advancing, the knock sensor could keep you below 3500rpm. I would think the boat would have problems all the time though not just at high speed.

Just my experience from the truck world, but the boat setups could be different and I'm sure someone else has had similar problems in the past.

Temperature sensor will keep it from passing 3000 RPM if the sensor is bad, going bad or poor connection. Its part of the programming know as EFI phased warm-up. Its keeps you from running at higher RPM till the engine is warmed up.

Thanks for the advise! Still working on it...in process of seeing what fuel pressure I have to the fuel rail today...installed new pressure regulator and same results...thinking maybe a bad or stuck injector...?? If it is I should see a pressure spike at the rpm that it starts to sputter...

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Originally Posted by Bdtlvs

Thanks for the advise! Still working on it...in process of seeing what fuel pressure I have to the fuel rail today...installed new pressure regulator and same results...thinking maybe a bad or stuck injector...?? If it is I should see a pressure spike at the rpm that it starts to sputter...

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Have you checked for any stored codes? What did your fuel pressure gauge read when you changed the regulator? This is the perfect example as to why I bought a scan tool. Its usually a whole lot cheaper in the long run than to keep throwing parts at it.

I didn’t check the fuel pressure before I changed the fuel pressure regulator....my bad! The pressure was 60psi at the rail when startup and stayed the same even at the point when it starts to sputter....! I’m kinda thinking timing issue maybe?? I ordered a new distributor cap and rotor to start out....plugs and wires look great..was thinking of changing the coil/module next....

Quote:

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Originally Posted by Bdtlvs

I didn’t check the fuel pressure before I changed the fuel pressure regulator....my bad! The pressure was 60psi at the rail when startup and stayed the same even at the point when it starts to sputter....! I’m kinda thinking timing issue maybe?? I ordered a new distributor cap and rotor to start out....plugs and wires look great..was thinking of changing the coil/module next....

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Good process of elimination. 60psi is what you want at all times. Fuel delivery is not your problem. Now it could be injectors but it would sputter at all times not just at 3400rpm and beyond. Spark is next on the list. How does it start up? Does it crank long or fire immediately? Any codes?

It fires up awesome and runs great all the way up to around 3800 rpm….no hesitation or anything….i don’t see any lights on anywhere at all.
I got a new distributor cap and rotor coming today that I’ll install and see, the distributor cap had some pretty good black sut around all the terminals and on the rotor so I hope that’s the answer! Maybe cross firing?? I also ordered a new coil

So installed new cap and rotor and same result….next will be coil.
I’m wondering if I can adjust the distributor at all??

My 06 outback did that after a few months from new. It was low on oil and went into a limp mode due to low oil pressure. It was using an incredible amount of oil from new and they did end up doing some motor work to fix it. No oil use since then and still running great with almost 200 hours on it.