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2005 Malibu Waksetter - Maintaining RPM / Fuel Issues?


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I have a 2005 Malibu Waksetter, 340Monsoon 5.7 engine.  I'm running into issues when gas tank gets to about a half a tank.  (I run premium all the time, but live in CA, so gas quality sucks!)

Boat runs great at all RPM, then about at half a tank, it's starts to loose power (RPM).  After shutting down for a few minutes, it runs fine, then happens all over again.  

Boat has recently been fully tunes up including replacing injectors, as part of trying to trouble shoot the issue, and it is still happening again.  (I've owned the boat since 2009 and other than doing annual service, I have literally had ZERO trouble with it until now.)

I've been told to look at possibly a 6 PSI Trip Marine Oil Pressure Switch (not sure why?)  Was told by an '06 Waksetter owner who said it solved their similar problem.  I've been told to replace fuel lines and also the fuel pump.  Could this also be caused by onboard computer issues? 

Appreciate any guidance or suggestions you may have.  Many thanks, dpr

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BCJohnsontx

Hello @dpr  I have a 2006 of the same model, same engine and I had a similar experience this weekend for the first time. Mine was only while surfing and under load, is your RPM issue all the time?

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Hi @bcjohnsontx It's happened with both under load and not.  The times it's happened has been when the tank is about half full.  Once it's starts, I can shut off for a few minutes, then it'll go under full / normal power, then start to lose RPM again.  (at least I'm able to limp back to shore with it) 

I was looking at some other posts under "Limp Mode" and the behavior is similar, but not exactly the same.  

I'm not a gearhead or mechanic, but have been around engines enough to understand how they work and it seems like it could be fuel filters / pump, or bad fuel lines, OR could the computer (ECM?) be doing something goofy to cause it?

Thanks,

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It sounds like your fuel system may have an issue.  Use a fuel pressure gauge to make sure that you have constant 42-44 PSI at key on, idle, and wide open throttle while it is happening.

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Thanks @justgary after talking with mechanic, he thinks it could be a crack in the fuel pickup in the tank or fuel pump. As issue only seems to happen around a half tank of gas, could be the pickup. (Hopefully, as it’s an easy fix). He wants me to take it out and run it with a full tank to verify.  Question: have you ever heard of fuel lines breaking down or corroding inside of the?  Will keep everyone posted. 

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BlindSquirrel
6 minutes ago, dpr said:

 Question: have you ever heard of fuel lines breaking down or corroding inside of the?  

Yep. I've seen several that looked good on the outside that were leaching off small pieces plugging the injector filters. Also saw one that broke down so much it had a flap on the inside causing fuel restriction. With the age of your boat, and as cheap as the hose is... Might be a good idea to change them anyway. Ethanal loves to eat rubber.

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Awesome @BlindSquirrel thanks for the info. I have a brother-in-law who is an old farmer (who works on a lot of farm equipment) told me the same thing. 

After I get it back in the water to test, if I need to replace the fuel pick up / fuel pump, I’ll also replace hoses.  As I mentioned in my original post, I’ve had this boat since 2009 and have literally had zero problems with it, so as much as frustrating this is to trouble shoot, I also feel I’ve been lucky as hell as well. Thanks again. DPR

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Have you replaced the inline filter between the tank and the fuel pump?  Mine a 1996 LX was located above the fuel tank behind the seat back. My neighbor (2005) had the same problem last year. It was a quick $12 fix.  3/8 barbed inline filter, 40 micron (WIX33482)  (NapaGold:3482)

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thanks @MoonDawg I’ll have a look. 

However, when talking with the mechanic, he said there wasn’t fuel filters on this engine.  He said the filter is at the injectors, which I replaced, because it was only $80 more than just having them cleaned. Is this correct?

i originally went in there saying it was fuel filters and / or fuel pump, but he said the they tested the fuel pump and it was fine. 

Question, do you know where I can get a schematic of the engine and where everything is? My original manual was stolen a few years back. Thanks again, dpr

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30 minutes ago, dpr said:

thanks @MoonDawg I’ll have a look. 

However, when talking with the mechanic, he said there wasn’t fuel filters on this engine.  He said the filter is at the injectors, which I replaced, because it was only $80 more than just having them cleaned. Is this correct?

i originally went in there saying it was fuel filters and / or fuel pump, but he said the they tested the fuel pump and it was fine. 

Question, do you know where I can get a schematic of the engine and where everything is? My original manual was stolen a few years back. Thanks again, dpr

You will probably find a filter near the tank, as @MoonDawg says.  The pump itself does have a screen at the inlet, but it would give you more trouble at WOT and not just at a specific tank level.

You said you would replace the fuel lines if you needed to replace the pump or pickup.  They are different, and one can have an issue without the other.  You have to figure out what the problem is, and then fix that problem.

The "mechanic" tested the fuel pump and it was fine... does this mean that he knows the fuel pressure stayed constant while the problem was happening?  I bet you a beverage that it isn't.  You could cut to the chase an remove the pickup from the tank and inspect it.  Your issue definitely sounds like it has a leak.  Other than that, consider the following steps:

1.  Test the fuel pressure at key on, idle, and WOT.  They should all be the same.

2.  Test the fuel pressure while the problem is occurring.  It should be the same.

3a.  If it isn't the same, rig up an external tank with fresh hoses and run the engine from that.  If it happens again, the problem is in your engine.

3b.  If it doesn't happen while running on the external tank, suspect the fuel pickup (cracks or holes), fuel lines, or possibly a filter you haven't found.

3c.  If it is the same, your problem is either not fuel related or it is injector related.  Have you done a tune-up recently (plugs, wires, cap, rotor)?

 

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Not really  filters on the injectors. There are wire baskets in them, but if they get trash in them or clogged, then the cylinder will run lean and you lose power. Better to add a high pressure filter after the fuel pump that you can change , but that’s another thread . My tank pickup had two parts. One part actually had fell off and fished it out and put it back together  

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