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Monsoon 340 stopping at 3,500rpm when surfing


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BCJohnsontx

Hello everyone. I am hoping one of you here has a quick solution to a new problem I have been running into on my last few trips out. 

Boat: 2006 Malibu 23 LSV with the 340 Monsoon engine. Pretty much stock engine except for a muffler delete and FAE system. All tuned up this year, no issues on several trips after. 

Here is my issue, starting a few weeks back. When surfing, occasionally the boat is holding right at 3,500 RPM and even with the throttle all the way down I can't get any more power out of the engine, even through I know it is there. What is strange is this only happens while surfing. When the ballast is even partially unloaded and the Power Wedge is up, I can have all the power I need and run the RPM's up to 5,000+. 

I have narrowed this down to something happening when the boat is a**-heavy (more nose up) in surfing mode. What is really strange is that it does not happen all of the time. Some surfs are great and I get all the power I want, then the next few will be sluggish. I can pull tubes, run down the lake, etc with no issues. My best guess is that there is some kind of computer trigger when surfing that is limiting the engine RPM's / power. 

Things I have tried so far:

  • Turning on/off cruise control
  • Powering down and cutting battery power for up to 10 minutes (reset)
  • Putting recommended amount of sta-bil in fuel

My current hypothesis(s):

  • Water in fuel that is getting picked up by fuel tank pickup when boat is more angled nose-up/a**-down, possibly causing the engine computer to do some things that limit power
  • I read a post on the forum that said something about a possible faulty fuel sending unit, telling the boat its very low on fuel. Not sure if this boat/engine has some kind of low fuel power limiter or not?

Next steps unless someone here has other ideas:

  • Siphon out all the remaining Fuel in the tank, check it for water, then refill with fresh gas and a bit of Sta-bil or Seafoam
  • Pull the fuel sender and check it along with looking into the tank for any debri, stuff in pickup, etc. 

 

Thanks everyone

 

 

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BlindSquirrel
9 minutes ago, BCJohnsontx said:

Hello everyone. I am hoping one of you here has a quick solution to a new problem I have been running into on my last few trips out. 

Boat: 2006 Malibu 23 LSV with the 340 Monsoon engine. Pretty much stock engine except for a muffler delete and FAE system. All tuned up this year, no issues on several trips after. 

Here is my issue, starting a few weeks back. When surfing, occasionally the boat is holding right at 3,500 RPM and even with the throttle all the way down I can't get any more power out of the engine, even through I know it is there. What is strange is this only happens while surfing. When the ballast is even partially unloaded and the Power Wedge is up, I can have all the power I need and run the RPM's up to 5,000+. 

I have narrowed this down to something happening when the boat is a**-heavy (more nose up) in surfing mode. What is really strange is that it does not happen all of the time. Some surfs are great and I get all the power I want, then the next few will be sluggish. I can pull tubes, run down the lake, etc with no issues. My best guess is that there is some kind of computer trigger when surfing that is limiting the engine RPM's / power. 

Things I have tried so far:

  • Turning on/off cruise control
  • Powering down and cutting battery power for up to 10 minutes (reset)
  • Putting recommended amount of sta-bil in fuel

My current hypothesis(s):

  • Water in fuel that is getting picked up by fuel tank pickup when boat is more angled nose-up/a**-down, possibly causing the engine computer to do some things that limit power
  • I read a post on the forum that said something about a possible faulty fuel sending unit, telling the boat its very low on fuel. Not sure if this boat/engine has some kind of low fuel power limiter or not?

Next steps unless someone here has other ideas:

  • Siphon out all the remaining Fuel in the tank, check it for water, then refill with fresh gas and a bit of Sta-bil or Seafoam
  • Pull the fuel sender and check it along with looking into the tank for any debri, stuff in pickup, etc. 

 

Thanks everyone

 

 

I'm betting it is just too much weight for the way it's propped. Kind of like, if you ever drove a manual car and shifted too soon or left it in a high gear when you needed to down shift. You can give it all the throttle you want, but it wont give you more RPM. You might just need to get a more aggressive prop.

Edited by BlindSquirrel
  • Like 2
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BCJohnsontx
2 minutes ago, BlindSquirrel said:

I'm betting it is just too much weight for the way it's propped. Kind of like, if you ever drove a manual car and shifted too soon or left it in a high gear when you needed to down shift. You can give it all the throttle you want, but it wont give you more RPM. You might just need to get a more aggressive prop.

I actually updated the prop this year to a more aggressive one. I can't recall exactly what prop that was right now (got it from Nettles locally) The new and old prop always handled surfing just fine in the past so I am not thinking that is not the issue right now, especially since sometimes the current prop/setup surfs great with power to spare. 

  • Like 1
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  • 3 weeks later...
MuchoAloha

@BCJohnsontx So my boat is having the exact same problem. I have a 2020 A24 with the M5... Im at sea level in Houston... bought it with 120hrs on it (has 240 now). Surf 90% of the time. Surfing on port side, RPMs hung around 3,800 maybe more depending on weight + wedge and would def pick up to 4,000+ when it needed... All of the sudden one day, MIL light came on a few times and threw codes 4237 and 4239. First issue or service light to ever come on. Turns out, it was O2 sensors on cats showing fuel burning rich. Pretty sure I got bad gas. So I changed the plugs, new tank of premium and two bottles of seafoam. Next time out, no more MIL light at all. Codes showed inactive.

Since then,  same issue as you. Nothing over 3,500 in surf mode... out of surf mode can open all the way to 5,000 with the same amount of weight... no issues. I have the ACME 3077 prop... I know for a FACT it's not weight related... so I took the boat to a tech, he plugged up, cleared the codes and ran the engine for a while (on the trailer) and he said everything looked perfect. Even after clearing the codes, boat still will not go over 3,500 in surf mode. In fact, if it gets to 3,500 too fast, the boat will straight up back way off the RMPs and then slowly creep back up.

Just dropped it off at the dealer this morning so we'll see what happens, they seemed a bit confused as I explained it... which makes me nervous. 

Keep me posted on how things turn out for you. Ill do the same.

Edited by MuchoAloha
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