2006 Mercury 25 hp efi losing power

[Duckhunter07]

Hi everyone,

I am new to this forum and am having some issues with my 2006 Mercury 25 hp 4 stroke efi motor. The problem I am having has occured on three different occassions with all being in 50 and below weather. The motor is electric start and when I go to start it in the morning I have to press the starter about 5 times before it will start. With each time being held for about 5 seconds. Not the worst part, but I guess the point is it doesn't start the best. The issue I am having lately is a loss of power on my way home from duck hunting. All the way to the spot whether it is 30 minute ride or less my boat will top out at about 25 mph with just me in it (1648 lowe) which is normal and run great! While hunting the motor can be sitting anywhere from 3-5 hours. Once I start it again it seems that the idle is slightly rough and a little lower than normal. The main problem is that when I plane off and give it full throttle it only does about 22mph and feels sluggish. Every couple minutes of driving the speed drops by a half mile and hour until I get down to 19mph on the gps. I can tell the rpms are dropping as well. I finally make it home and the next time out it is completely normal again.

This weird problem did start occurring after I used 87 octane 10% ethanol gas. Immediately after the first day I drained that gas and put premium back in.
The impeller is pumping a strong stream of water. No alarms go off on the motor for overheating or low oil pressure

Can anyone explain why this may be happening? I have looked into a few different fuel flow related issues with none being a success. I am just looking for a starting point because I am confused as to while it only happens on the way home after sitting. Thanks.

 

[QBhoy]

I’d start with the very obvious, not knowing much about the basic history of the engine.
sorry if it’s child’s play to you, but what about the following to start with;

check fuel filter or even better. Change it. If it’s like mine you’ll have one in line under the hood and perhaps even a water separator type inboard too.

check the plugs are good or change them.

check it’s putting out a charge voltage (if applicable to you)

check the compression

check the oil isn’t thinned and diluted with fuel or worse, water.

 

[Duckhunter07]

Thanks for the ideas! So far I have..

-Changed the sparkplugs

-replaced the fuel line

-Ruled out the fuel tank and vent

-Checked the compression cold Cylinder 1: 110 2:115 3: 108
Since they are all relatively similar I am not too worried about compression. Plus my gauge isn't the best.

-I have plans of replacing the fuel filter, but I pulled it out and it seemed to look good.

-I checked the oil yesterday. The level and color looked normal. It is not fresh, but looks normal. How do I test to see if it is diluted or thinned?

I looked for a water separator, but I did not see one. I was wondering if that may be just inside the VST. Do you think this problem could have anything to do with the VST?

I am also getting more concerned with the starting issue. Being a EFI I would think it should fire up relatively quickly even in cold temps. It almost seems as if the fuel delivery system is not feeding the motor more fuel for cold starts so it takes multiple times turning the motor over to give it the appropriate amount of fuel. Is there a sensor on the motor that may not be reading temp correctly or something of that nature?

 

[QBhoy]

If there is a water separator. It will be in the boat and between the tank and the engine. Change that in line filter at the least

 

[Duckhunter07]

From the tank to the motor is looking like the fuel goes to these parts in order
-fuel line
-fuel fliter
-mechanical fuel pump
-fuel cooler
-VST
-injectors

I did not see a water separator anywhere yet. I am guessing the problem needs to be in one of the above systems.I have narrowed it down to the mechanical fuel pump, VST, and injectors...

 

[Duckhunter07]

Hey guys,

I am not sure if anyone has had this same problem, but I finally figured it out! After going through most of the fuel system I decided to dig into the VST. Im so glad I did because the bottom of the tank was absolutely filled with orangish sludge that was clogging the pickup screens to the electric fuel pump. As I would drive further more of the sediment on the bottom must have been getting sucked onto the screen causing a lack of fuel flow which would slow me down. Then after I would be done for the day some of the sediment on the screen must have dropped back down to the bottom of the tank starting the process over! To whoever read or tried to help out I appreciate it! Thanks.