Please Help. Won't go past half throttle.

[Direw12]

I have a 2003 SeaDoo Speedster V6 240EFI. The boat was sitting for about 5 years and before I took the boat out on the water this year, I replaced the alternator, belt, spark plugs, radio, speakers, bilge pump and changed the gear oil in the jet pump assembly.

When I took the boat out the for the first time, the boat didn't run that well. The boat would bog down when you tried to give it throttle and it didn't sound like it was idling well either. I did some research (on here) and found out that the fuel filters probably needed to be changed. (I know, amateur mistake) Once I put new fuel filters on, I took the boat out again and the boat ran so much better. The boat was idling perfect and responded better to the throttle. The only problem now is that the boat would not go past half throttle.

I did some more research (on here) and found out that the Cylinder head sensors apparently go bad for no reason on this motor and if your sensors are bad, the computer on the boat will think that the boat is over heating and limit your RPM's to around 3500-4000. (which is consistent with the half throttle problem) I just replaced the sensors and just to make sure that nothing was blocking the fuel line I replaced the fuel line filter one more time but unfortunately I still can't go past half throttle. The weird thing is that if I stop the boat and then start it up and quickly give it throttle, I can go almost full throttle and it seems like there is nothing wrong with the boat and performs great. BUT, as you drive it, it slowly goes back to the point where you can't go past half throttle again.

Please help. I'm not sure what else there is to do. Is there a heat sensor that I'm missing and need to replace?

Thanks.

 

[Dr Honda]

Before you changed the temp senders... did you even check them? I guess I can assume they weren't bad.

1) With a 2-stroke... it's VERY bad to keep running an engine that isn't running right. If it's a fuel issue... you can burn out the engine in short order. (The fuel still transports the oil into the engine) And, running lean will burn/melt the piston crowns

2) You can't guess on a fuel injection system. All senders can be checked.


As far as your question.... that engien has a bunch of sensors. There is:

1) TPS
2) Manifold air temp
3) manifold vac
4) Port temp
5) Starboard temp
6) water sensor

Since you have the newer 240... if any of those senders are out of range, or have a problem... the warning light will come on, and you will get a series of beeps from the sounder.

You can check all of them with a hand held meter... but a quick trip to a merc dealer, and they can scan all the senders at once, with their DDT system. I don't like sending people to the dealer... but for 15 min worth of labor ($$) that can tell you quick if a sender is dead. (They can see it, and then can read any history)


OK... with that said... when is the last time you changed your sparkplugs? If one or two are dead... you will drop a full 1500 RPM per. (up top) You can have 2 dead plugs... and it will idle OK, and run up... but just fall on it's face around 4500 RPM.

On that thought... have you checked for spark on all the plugs? If you have a dead coil... you won't rev up either.

Next.... have you checked your fuel pressure? There is more than one filter in your fuel system, and one is on the bottom of your fuel pump. If the high pressure fuel drops pressure... then you will go lean.

 

[Direw12]

Thank you very much Dr. Honda. Your response was very thorough and I do appreciate you taking the time out of your day to answer my post. I will not be taking the boat out again until i go to a dealer and have the system checked. Let's hope it's nothing serious. (Fingers crossed) Thanks again, and when I get an answer on what the cause is, I will be sure to let you know.

 

[Direw12]

I did replace the spark plugs and gapped them per the owners manual before I first took the boat out but the bad fuel filter could have fowled them up so I will check them. I have not checked for spark yet but will after reading your post. The fuel filter on the bottom of the pump, are you referring to the water separator? If so, that has been replaced. Also, Any easy way of checking the fuel pressure?

 

[Dr Honda]

Nope. The filter I'm talking about is on the bottom of the pump, inside the vapor separator tank. A quick fuel pressure test will tell you if it's plugged up.