RPM lost at 2800 PCM Pro Boss GT40 Ski Nautique 96

If it is running smooth while this happens it may be a fuel supply issue.

I believe there is a valve in the fuel tank, that can be checked.

You can hook up a fuel pressure gauge and run the engine, that would let you verify quickly if it is fuel or ignition related. Fuel pressure should not drop when you accelerate, it should increase to offset loss of vacuum when accelerating.

There is a GT40 specific help section on this forum that keeps the most frequent failures recorded.

Ok Thank for the fast reply 😊 will check tomorrow. Before this years season started i did change the fuel filter maybe it stucks there 🧐

Running good up till 2800 rpm makes me think your engine may be going into "limp mode"

The link below has a description from the manual in the post by Lewy2001 that might be helpful

Like he says, removing the wire from the water temp switch and the oil pressure switch one at a time and running the boat will tell you if that's the problem.

You can have normal readings on the oil pressure and water temperature gauges which are fed from sending units that are different pieces of equipment from the switches so the indications can look and be right, but a defective switch will put you into limp mode.

It's quick and easy to check and maybe you'll find the problem is one of the switches or at least it will let you rule them out as a cause.

link

KENO wrote: Running good up till 2800 rpm makes me think your engine may be going into "limp mode" The link below has a description from the manual in the post by Lewy2001 that might be helpful Like he says, removing the wire from the water temp switch and the oil pressure switch one at a time and running the boat will tell you if that's the problem. You can have normal readings on the oil pressure and water temperature gauges which are fed from sending units that are different pieces of equipment from the switches so the indications can look and be right, but a defective switch will put you into limp mode. It's quick and easy to check and maybe you'll find the problem is one of the switches or at least it will let you rule them out as a cause. link

The pressure seems to be lower than it should its something between 40-50 i think need to check that also tomorrow. I saw the switch is available at nautiqueparts.com
Maybe there is also not enough oil but i checked it should be ok. Maybe put in a bit more and the pressure gets a bit better.

When my GT40 went into limp mode 5 years ago it did not run smoothly. It was very rough.
I got back to the dock with it stuttering and without enough power to get up on plane with an empty boat, only 2 people on board.   It sounded like it was running on 4 cylinders.

Good advice on this forum had me replace both the Coolant and Oil Pressure sending units and the boat has never stumbled since. The boat was 19 years old so it did not bother me to replace them as maintenance. It seems to me there are 2 coolant sensors?
I also replaced the Thermostat at this time. One of these cured my issue but I don't know which as I did them all at once wanting to get back on the water.

MrMcD wrote: When my GT40 went into limp mode 5 years ago it did not run smoothly. It was very rough. I got back to the dock with it stuttering and without enough power to get up on plane with an empty boat, only 2 people on board.   It sounded like it was running on 4 cylinders. Good advice on this forum had me replace both the Coolant and Oil Pressure sending units and the boat has never stumbled since. The boat was 19 years old so it did not bother me to replace them as maintenance. It seems to me there are 2 coolant sensors? I also replaced the Thermostat at this time. One of these cured my issue but I don't know which as I did them all at once wanting to get back on the water.

The engine runs really smooth and also got enough power but over 2800rpm it stucks. Thanks for your feedback hope can solve the problem soon.

The engine light does not light up. But its impossible to go over 2800RPM everytime i try goes back to about 2600 and everything is going fine till 2800 and if i go above the same problem repeats. I go on the river in a few hours and will try to disconnect the temp and oil switch. Lets see what happens 😅 where can i connect the fuel pressure gauge?

Basler wrote: where can i connect the fuel pressure gauge?

There's a test connection at the front of the fuel rail usually referred to as a Schrader valve.

You need a test rig with the right adapter to screw on to the Schrader valve.

The valve resembles an oversized valve stem on a car tire, bike tire etc..

Like MrMcD said, "it costs zero to check" unless you have to buy the test rig, then the cost goes up some    But it's a handy tool to have

Checked now with the wire disconnection. I disconnected both water temp and oil pressure switch. It runs over 2800rpm when i accelerate in neutral now. Looks like i need to replace the oil pressure switch by the way i will change also the temp switch just to be sure its all good. When i disconnected the oil pressure switch, the gauge in the cockpit still shows the psi information. Is it possible that the gauge gets separate psi informations?

Basler wrote: Checked now with the wire disconnection. I disconnected both water temp and oil pressure switch. It runs over 2800rpm when i accelerate in neutral now. Looks like i need to replace the oil pressure switch by the way i will change also the temp switch just to be sure its all good. When i disconnected the oil pressure switch, the gauge in the cockpit still shows the psi information. Is it possible that the gauge gets separate psi informations?

Here's a picture courtesy of Lewy

He has the switch that puts you into limp (SLOW) mode circled in yellow. That switch has only one function in life......to tell the computer to put the engine into limp mode if it thinks oil pressure is less than 5 PSI.(and the computer puts the engine in limp mode and turns on the check engine light unless it's burned out)

Right next to it in the picture with the light blue wire hooked to it is the oil pressure sending unit whose only function is life is to feed a signal to the pressure gauge on the dash.

Two totally different pieces of equipment, they both sense from the same point with a tee in the line.

If the switch goes bad, it'll put you in limp mode even though oil pressure is normal.

You should see normal pressure on the dash gauge before cruisin' around with the switch disconnected

If the boat runs good with the switch or switches disconnected and your gauge readings are normal, I'd use the boat just like you always have while the parts are on order.

Before the Protec engines and the GT40's came along the engines
didn't have this "additional protection" feature

Some people might call it a nuisance that causes more problems than it prevents especially if you pay some attention to the gauges

This may be a silly question Basler, but would the engine act up in neutral before you disconnected the wires or was it only under load ?

The reason I ask is because in neutral you can rev an engine real easily with very little fuel demand and maybe you think the problem is solved and then when you get on the water you could have the same issue show up.

If you don't know the answer to the first question, I'd try reving it up in neutral with the wires connected again and see what happens.

I'd hate for you to think it's all figured out and then find out it's really a fuel supply issue when you run it under load

KENO wrote: This may be a silly question Basler, but would the engine act up in neutral before you disconnected the wires or was it only under load ? The reason I ask is because in neutral you can rev an engine real easily with very little fuel demand and maybe you think the problem is solved and then when you get on the water you could have the same issue show up. If you don't know the answer to the first question, I'd try reving it up in neutral with the wires connected again and see what happens. I'd hate for you to think it's all figured out and then find out it's really a fuel supply issue when you run it under load

The problem shows also in neutral we did reconnect the sensor and also in neutral it stucks on 2800 when disconnected 3000RPM there is no issue with the rpm limitation. Im sure the sensor is defective. Yes would be hard this would not be the solution but with this im sure (hope) this will work with a new one 😅

KENO wrote: Sounds like the switch is the problem, just wanted to verify what you did. By the way, your English is much better than I could speak any of those 4 official languages of Switzerland

Google is my friend but yeah i almost only speak swissgerman, a bit french and can understand 1% italian 😅🙌 70% are talking swiss german here

You don't say whether that oil pressure is with cold oil or warm oil or what speed the engine is running, but that pressure is good and nothing to really worry about especially if it's warm oil and you're on plane at cruising speed.

Whatever difference you see could be due to differences between the new gauges vs old gauges.