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Low power at high RPMs


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I have a 2004 Sunscape with the 340 monsoon, and as the title states it’s bogging down at higher rpms. 
 

When I start it up, I get the beeping sound but it idles and runs fine. All gauges on the dash look normal. I can give it throttle in neutral with not hiccups. When I shift it into gear, it runs normal until I start giving it more throttle. 
 

At higher RPMs it bogs down and won’t go any more. Doesn’t stall or anything, just reaches a point where it won’t accelerate. 
 

I replaced the spark plugs with no luck. Ordered a new fuel filter so maybe that’ll do the truck. I tried cleaning the intake of the fuel pump with carburetor cleaner as suggested on here, but that didn’t do anything. I haven’t actually tried taking the boat out and running it because I am still getting the constant beeping noise at startup.  
 

What else can I replace or check before I replace the fuel pump? Any sensors that could be the culprit?

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If you are getting a constant beeping alarm after starting the engine you may be experiencing forced power reduction by the ECM did to a fault code.  Use a code reader to see if there are any faults.

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16 minutes ago, csleaver said:

If you are getting a constant beeping alarm after starting the engine you may be experiencing forced power reduction by the ECM did to a fault code.  Use a code reader to see if there are any faults.

Does that mean it needs to be cleared? Other than the beeping nothing else seems to be wrong. Like I said, I haven’t tried to run it because of the constant beeping but as far as I can tell everything else is working. 
 

Last week my engine temp gauge stopped working but has since returned back to working order. Could this have caused the beeping?

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An ECT (engine coolant temperature) over temp can cause power reduction whether the engine is actually overheating or if the ECM just thinks the engine is overheating due to a faulty sensor, wiring, or ECM. 

Without knowing what is causing the alarm it is very difficult to recommend what you should do about it.

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1 hour ago, Chase0808 said:

When I start it up, I get the beeping sound but it idles and runs fine.

Does it continue to constantly beep, or does it turn off at some point? 

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The beeping is constant. While idling it would occasionally stop for a few seconds, then start back again. But generally, it is a constant beep as soon as I start the boat up. I have a neighbor that has a computer to read the codes, I guess I can wait until he’s able to come by and check it before I order anything. 

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1 hour ago, justgary said:

Just for kicks you could test the fuel pressure at key on, idle, and wide open throttle.

Yeah I think this will help to narrow things down. Just have to go buy a fuel pressure gauge. 

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43 minutes ago, Chase0808 said:

Yeah I think this will help to narrow things down. Just have to go buy a fuel pressure gauge. 

Well, it may not be quite that easy.  The 2004 model has the test valve placed directly under the lip of the plenum cover.  You will either need to adapt a tire chuck to your gauge or cut the flange away so you can thread your regular gauge on.  I have seen several with the flange hacked away over the valve.

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Posted (edited)

Correct me if I’m wrong, the plenum is the plastic engine cover? If so, mine didn’t come with one. I believe I see the test valve on the port side fuel rail. 

Edited by Chase0808
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3 hours ago, Chase0808 said:

Correct me if I’m wrong, the plenum is the plastic engine cover? If so, mine didn’t come with one. I believe I see the test valve on the port side fuel rail. 

The plenum cover is an aluminum casting held down by two rows of socket head cap screws.  If you can get your gauge on the fuel rail, great news.  Please post a photo of how you did it.

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Not my boat, but this is pretty much exactly what my engine compartment looks like. I can’t tell from this picture, but it looks like there’s a valve on my port side fuel rail at the front (towards the bow). Hopefully this all makes sense. 

A8CAB72A-142B-499C-9E84-CDDD4AB9E5F3.jpeg

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1 hour ago, Chase0808 said:

Not my boat, but this is pretty much exactly what my engine compartment looks like. I can’t tell from this picture, but it looks like there’s a valve on my port side fuel rail at the front (towards the bow). Hopefully this all makes sense. 

A8CAB72A-142B-499C-9E84-CDDD4AB9E5F3.jpeg

Then you don't have a 2004 Monsoon like you said you have.  They look like this:

spacer.png

The throttle body is visible in the upper right corner of the image.

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2 hours ago, Chase0808 said:

Wow, this whole time I thought it was the 340. Is my motor the 320 LCR?

I don't know what you have, but I bet a fuel pressure test is easier than on what you don't have.

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Looks like mine is a 320 LCR. I’ll try to get on testing the fuel pressure. If I have low pressure, is it likely going to be a bad fuel pump? I’ve read that people hear a whining noise coming from it when it’s about to go out. I don’t really hear any noise from it and it appears to be working. I am still getting the constant warning beep from the dash though. 

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Update: 

So far I’ve replaced the plugs and fuel filter. Took it out just now and ran it. It’s still bogging out on me at higher rpms but I can get it up higher than before. It sounds like it’s starving for fuel. Under load, I think I can hear more of a whining noise from the fuel pump. Still getting the constant beeping.

 

Would a lack of fuel cause the beeping noise? Or maybe I need to try cleaning the fuel injectors?

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On bakes the replacement pierburg pump is $315 but I found the same fuel pump for $239 on marinepartssource.com. Has anyone ordered from here? 

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1 hour ago, Chase0808 said:

I’ll try to get on testing the fuel pressure.

Honestly, you can keep guessing and throw expensive parts at it if you want to.  A pressure test will tell you if your pump is good.  Odds are that it is bad, but at $300 I would confirm it first.

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51 minutes ago, Chase0808 said:

On bakes the replacement pierburg pump is $315 but I found the same fuel pump for $239 on marinepartssource.com. Has anyone ordered from here? 

Read this entire thread before buying a pump so you get what you need.

 

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I have my neighbor coming over today with his computer to read any codes and he also has a fuel pressure gauge. 

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I’m getting high fuel pressure at idle. 80 psi. Going to start with the fuel pressure regulator. I have one at the fuel rail and one down by the fuel pump. Has anyone replaced either and found any luck?

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I had to replace a fuel pressure regulator due to the high pressure in a 2001 VLX I had at one point.  The regulator was near the fuel pump on my Monsoon engine.

It looked like this and I found it on ebay for under $80 iirc by just searching for the part number that was on it once I pulled it off the boat:

https://www.bakesonline.com/indmar-fuel-pressure-regulator.html?gclid=CjwKCAjwmK6IBhBqEiwAocMc8g0PzS8-ZUQvZ38GedGgNhdrF6wmvkaxaNFeDg76W5ZkGIcwdoehkBoCt-UQAvD_BwE

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