60hp Merc intermittent power loss

Mike6723

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Jul 21, 2020
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Hi, my name's Mike, I've been a longtime browser of this website, but first time posting. I am hoping someone has some ideas to help me...I have a 2005 60hp Merc bigfoot EFI on my pontoon boat, and I have been experiencing some power loss which is progressively getting worse. The issue occurs ONLY at around one third throttle or higher where the boat will suddenly lose power after running fine for a short time, as if the throttle is being pulled back. I have to then pull the throttle back to idle speed or it will stall. If I wait a few seconds I can throttle back up and continue on. Also, if I keep the speed low the motor runs just fine. This began last season, only happened once or twice, now this season it has gotten worse to where it happens all the time. I have replaced both fuel filters, and there is no change. I also changed the thermostat after I got a temperature warning once, but I'm not sure these 2 things are related, no heat warnings since. Thank you to anyone who can point me to what I should look at next.
 

Texasmark

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Dec 20, 2005
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Easiest first data point is to squeeze the bulb when the problem occurs and see if it helps. If bulb collapses in your hand, check fuel tank venting, or could have crud in the fuel line from the tank....little tan specks of foreign material. Second data point, if you squeeze the bulb and the engine immediately recovers, suspect the fuel pump or cracked, fuel lines, both in the engine and the feed line from the fuel tank. Third, if crud is found in a fuel line, replace the fuel filter in the engine.

If none of that works, time for plan B. Come back.
 

Mike6723

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Jul 21, 2020
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Thanks for the quick response, I will try the bulb next. I have already changed both fuel filters, another thought was maybe the pickup tube in the gas tank is gummed up, I assume there's a screen on
 

ET 1978

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Jul 26, 2020
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I have the same motor and issue. I'm good until I go over 3500 rpm and the it will be fine for a little while and then start surging.
 

Mike6723

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Jul 21, 2020
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Ok, I'm back, experiencing same problem this year. I brought the boat into the shop last fall, and due to covid and the time of year they could not do a water test, but they did change the spark plugs, they said that could be the cause...anyway, first time out this year same issue. I am at a loss on what it could be as I've changed out all the obvious things. Any ideas, even far fetched ones? Could a bad sensor be causing this?
 

Texasmark

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Did you do the bulb test? Answering this question will bump you back to the top for better visibility for someone more knowledgeable to see.
 

Mike6723

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Jul 21, 2020
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I did the bulb test on the weekend and the engine recovered after maybe a half second delay, and then ran smoothly. I have a new bulb/fuel hose which I will install next weekend, hopefully the bulb was the problem, we'll see
 

Texasmark

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Passing that test and running smoothly tends to tell me that you have a clog in the fuel distribution system somewhere. The fuel pump sucking couldn't dislodge the culprit but the extra pressure Pushing rather than Sucking did. I'd revisit fuel filter in the engine, and fuel strainer in the tank and internal and external fuel lines for black specks or tan crisp, semicircle chips (internal and external. If you used any kind of water absorber, and ethanol is such, if there is an adequate supply, it forms a gooey blob and will clog your fuel line...had that stop me in the middle of a large/rough lake one day...clogged right at the connector that mates the tank's fuel line to the engine connector.
 

Mike6723

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Jul 21, 2020
Messages
9
Passing that test and running smoothly tends to tell me that you have a clog in the fuel distribution system somewhere. The fuel pump sucking couldn't dislodge the culprit but the extra pressure Pushing rather than Sucking did. I'd revisit fuel filter in the engine, and fuel strainer in the tank and internal and external fuel lines for black specks or tan crisp, semicircle chips (internal and external. If you used any kind of water absorber, and ethanol is such, if there is an adequate supply, it forms a gooey blob and will clog your fuel line...had that stop me in the middle of a large/rough lake one day...clogged right at the connector that mates the tank's fuel line to the engine connector.
 

Mike6723

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So i changed out the fuel line and bulb, and the issue is still there. Checked the dip tube in tank (it's a built in tank) and the screen seemed spotless. Just to be sure, I then took it out for a run, with the fuel line put directly into a 5 gal Jerry can. It ran perfectly at high rpm for an extended period of time, no issues at all! So I concluded that maybe the gas filler cap is not venting properly so I went for another run with everything hooked back up properly but I left the gas cap open, runs perfectly! Visually nothing seems wrong with the cap (it's a perko vented cap assembly) and I can get one on amazon for $45 cdn, could it be so simple? By the way I've never run anything but premium fuel (no ethanol) and like I said I replaced both fuel filters last year.
 

Mike6723

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Jul 21, 2020
Messages
9
So i changed out the fuel line and bulb, and the issue is still there. Checked the dip tube in tank (it's a built in tank) and the screen seemed spotless. Just to be sure, I then took it out for a run, with the fuel line put directly into a 5 gal Jerry can. It ran perfectly at high rpm for an extended period of time, no issues at all! So I concluded that maybe the gas filler cap is not venting properly so I went for another run with everything hooked back up properly but I left the gas cap open, runs perfectly! Visually nothing seems wrong with the cap (it's a perko vented cap assembly) and I can get one on amazon for $45 cdn, could it be so simple? By the way I've never run anything but premium fuel (no ethanol) and like I said I replaced both fuel filters last year.
Ok, problem is back now, so frustrating...went out just now and it bogged down twice. This issue is so randomly intermittent, I will start checking fuel lines in the engine next
 

Texasmark

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Get a companion and go out with the engine cover off. While they take care of the helm, you get back there and start wiggling fuel lines including the line from the tank, including both ends. Then take the cap off again and see if it makes any difference. On outings where it worked and didn't what kind of wind-water conditions did you have in both cases?
 

Mike6723

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Jul 21, 2020
Messages
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Get a companion and go out with the engine cover off. While they take care of the helm, you get back there and start wiggling fuel lines including the line from the tank, including both ends. Then take the cap off again and see if it makes any difference. On outings where it worked and didn't what kind of wind-water conditions did you have in both cases?
Ok, I'll try that next...the time it worked it was quite windy, but I did go into a bay for a while where the water was much calmer. Like I said, I drove around for quite a while at high speed with no issues whatsoever. Later in the day, water was calm and the problem came back twice.
 

Mike6723

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Jul 21, 2020
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Ok, this should be the last post on this topic...I decided to take apart the fuel pump to see if that was maybe the problem, and sure enough the little round valves were torn, and one of the small rubber fasteners was actually broken in half! I am actually surprised it still worked as well as it did with all the small broken pieces floating around in there. Anyway, I couldn't find a rebuild kit online and my local marina didn't even have one listed so I just bought a new one ($210 cad including tax ☹️) so hopefully that's the end of this headache! Thanks for all the help on this site!
 
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