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Stumble at WOT

Old 06-09-2019, 07:54 AM
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Default Stumble at WOT

2004 F225's. Running up to around 5200-5400 motors run like a top but If I push to WOT either while on plane or coming out of the hole one of the engines stutter and run like it's missing. Anyone have any ideas or suggestion. Injector, timing? It just started and runs fine otherwise. Thanks for any thoughts.
Old 06-09-2019, 08:39 AM
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Sounds like a fuel restriction. Maybe time for a new water separator.
Old 06-09-2019, 08:46 AM
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Had a similar isssue a few years back...after a lot of trouble shooting found the problem to be the check valve where the fuel line attaches to my fuel tank..it was all gummed up. Ran great after replacing.
Old 06-10-2019, 04:40 AM
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Thanks guys. I just got replacement separators so Ill start there and then look over any check valves.
Old 06-10-2019, 05:59 AM
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Check your spark plugs.....just had this exact same thing happen on my Mercury 150 Four Strokes. Would run at 4,000 rpm all day long, but when you tried to accelerate, one or both of the motors would have a "stutter" that felt like a rev limiter was kicking in. It was like it wanted to go higher, but couldn't....then it would clean up, hummers' along and then do it again. When it did it, it was a 400 rpm or so reduction and sometimes both motors would do it, neither would do it or it would alternate between one and the other. I could drop a couple hundred rpm, the problem would go away and it would run at that rpm no problem and if I slowly tried to accelerate (like 100-200 rpms) it would...but if I tried to accelerate faster, it would stutter. Sometimes would do it around 3,500-3,800 rpm, but mostly above 4,000 rpm.

Took it into the shop and they said it had to be the fuel system....I told them no, it wasn't fuel related and they didn't believe me. So, they changed all the lines and filters between the tanks and the motors and it still did it. Finally convinced them to come to my house so we could water test it and I could show them exactly what it was doing. They hook up the computers and it should no error codes or faults and when running and I could get it to do it, other than the rpm drop, nothing showed up on the computer. Guy decided to change all the spark plugs to eliminate them as the problem and found that the bottom two spark plugs on each motor showed minimal signs of water. Mechanic said that on all four strokes, due to how they share cooling and exhaust passages, that it is possible under just the right conditions (such as backing down in seas) that the water level inside the tuning chamber can get a little higher than normal and allow just a little water vapor to be sucked into the lower cylinder. Something about during the four strokes, it creates a split second of negative pressure inside the cylinder that will allow water vapor to be sucked into the cylinder.

So, to answer your question, before you go spending a bunch of time chasing down fuel system parts and replacing them, put in a new set of spark plugs and see if that makes your problem go away.
Old 06-10-2019, 10:11 AM
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Not hijack the op I have heard of people coming off plane to quick and blowing up their 4 stroke motors because of water getting sucked up into the exhaust valves and hydro locking the motor and bending valves.so yes it is possible and you should try to not just jump off of plane and stop with any boat let alone a 4 stroke motorGood luck and let us know what you find fixes your problem.
Old 06-10-2019, 11:01 AM
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Originally Posted by dogslife View Post
Not hijack the op I have heard of people coming off plane to quick and blowing up their 4 stroke motors because of water getting sucked up into the exhaust valves and hydro locking the motor and bending valves.so yes it is possible and you should try to not just jump off of plane and stop with any boat let alone a 4 stroke motorGood luck and let us know what you find fixes your problem.

The mechanic said that is what was happening to mine to a much lesser degree. Just enough water vapor was getting into the cylinder to show up, but not a great amount.....he did mention not coming off plane too fast. He said when that trailing wake hits the back of the boat and kind of lifts it up and pushes it forward, that is like shoving a water hose up the exhaust pipe on your car. It was just a small amount of discoloration and deposits caused by water on the lower plugs in each of my engines.
Old 06-10-2019, 11:10 AM
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I have had something similar happen when my grounds and other electrical connections needed to be de-tarnished.
Old 06-10-2019, 11:57 AM
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Originally Posted by stuartb91 View Post
Had a similar isssue a few years back...after a lot of trouble shooting found the problem to be the check valve where the fuel line attaches to my fuel tank..it was all gummed up. Ran great after replacing.
^^^This^^^
Old 06-17-2019, 01:52 PM
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Thanks for the responses guys. I have replaced the separators as they needed to be done anyway and the spark plugs are new from a maintenance about 20 hours ago. My hearing isn't very good so I hadn't noticed until it happened again this past week that when the motor stumbles and loses power an alarm sounds for just a second and shuts off. The motors are not hot and I have plenty of water flowing. Low oil pressure alarm? This makes me wonder if there is a low voltage warning alarm which would lean towards Stuartb91's experience. I will be checking all my grounds and check valves to confirm or eliminate the suggestions. Thanks again for the ideas.
Old 06-17-2019, 02:21 PM
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Just had an outboard on the dock doing this. Plugs were new as of a month ago. Decided to try a fresh set of plugs since it is cheap to do. New plugs fixed it.
Old 06-17-2019, 02:37 PM
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Originally Posted by Crpalp View Post
when the motor stumbles and loses power an alarm sounds for just a second and shuts off. The motors are not hot and I have plenty of water flowing. Low oil pressure alarm? This makes me wonder if there is a low voltage warning alarm.
There is no 'low voltage alarm"
If you are getting an audible alarm, it is for either high temperature or out-of-range oil pressure -
and with both of those the ECM will misfire some cylinders to bring the rpms down.
The ECM will also turn on a warning indicator - if installed - to show which alarm it is.

You might have a defective oil pressure sensor-
easy to swap it between engines and see if the problem moves.

Old 06-17-2019, 05:11 PM
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That alarm could be a low fuel pressure alarm.. That would make sense if it is only happening a WOT. In addition to the other fuel system items others have mentioned, you might want to look at your anti-siphon valve. I have had problems with that creating a low fuel pressure alarm before.
Old 06-17-2019, 07:11 PM
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Originally Posted by 59cruisers View Post
That alarm could be a low fuel pressure alarm..
there is no such thing on a "2004 F225"

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