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Motor loses power

6

660catman

New member
My 2008 Merc 90 4 stroke EFI will start fine, idle great but after a minute or so at full throttle will fall flat on its face. It’s like I pulled back on throttle to neutral. Once that happens it runs rough and then run fine. Idle for a couple of minutes then full throttle, it does it again after a minute or so. New fuel filters, new fuel line from tank and plugs have about 50 hours on them and changed in Aug 2021. Any ideas before I throw the parts cannon at it or take it to a dealer?
 
Put a fuel pressure gauge on it and see if your loosing pressure. If you do loose pressure start with the fuel filter and work forward thru fuel pump to injectors
 
I have a fuel pressure guage set coming to test that. If it does lose pressure, then it could be either the low pressure pump which fills the FSM, or the high pressure pump that feeds the injectors. The other thing is the float switch might be faulty / sticking in the high position thus shutting off the pump while still using fuel and running out. This controls the low pressure pump in the FSM. I have read that the float switch has been an issue with others. Although Amazon has a switch for 40 bucks, I’m leaning towards an OEM one for 227 bucks. Not very good reviews on the AM switch.
 
The other thing is the float switch might be faulty / sticking in the high position thus shutting off the pump while still using fuel and running out.
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Don't know your serial number, and also have not heard of a float switch working like that. Not saying is doesn't just have not seen one that worked that way
 
Thanks, that is different
All the ones I've worked on which were Mercruiser with VST it was just a float valve. It filled up and would not allow more fuel in until it was used up

Oh and one my current outboard motor serial number is 3B384246
 
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