I have a 2002 Lund with a 115hp Mercury EFI (Rebranded Yamaha I believe) that I noticed was down on power last time I took it out on Fort Peck. While I was there it also died once at the point right after I started it and pushed the throttle to where I can only assume the fueling changes as the exhaust note changes significantly and RPM jumps, I thought nothing of it at the time. I brought the boat home and did the maintenance I had planned to do this fall (fluid and spark plugs). I fired the boat up and ran it to circulate the oil, I gave it throttle and when I hit that same point in the throttle sweep, it died. This is repeatable and it dies at the same spot every time, If I push past that point quickly, I can sometimes keep it from dying but it does idle rough. I thought maybe it was a fuel pressure issue but after testing it, fuel pressure is consistent (right around 40PSI) even when I am able to keep the engine running at higher RPM.
I am trying to think of any other relevant information but I am not terribly familiar with boat motors, I know there are differences in the way the fueling works at the very least and I don't want to go around firing the parts cannon. I am comfortable working on the mechanical stuff, know how to use a multimeter as well and can do diagnostic work on automobiles easily but I am stumped by this and am not sure where to even go from here. I am happy to provide more information if needed. I am unable to find any sort of service documentation like the ford workshop manuals I have used in the past for my pickups.
Thank you in Advance,
Jacob
Edit: I found a repair manual, going to hold off on ordering it just yet but I do see they are available. I was looking for something for one specific motor or motor series but I see they have one that's all Yamaha and Mercury outboards from 95 to 04.
Knee jerk reaction is the throttle position sensor is the issue but checking the resistance it seems to be linear although I don't anybody to help me so I have to move back and forth from the throttle to the motor which makes it a little harder to see if there are any jumps or anything anomalous.
I am trying to think of any other relevant information but I am not terribly familiar with boat motors, I know there are differences in the way the fueling works at the very least and I don't want to go around firing the parts cannon. I am comfortable working on the mechanical stuff, know how to use a multimeter as well and can do diagnostic work on automobiles easily but I am stumped by this and am not sure where to even go from here. I am happy to provide more information if needed. I am unable to find any sort of service documentation like the ford workshop manuals I have used in the past for my pickups.
Thank you in Advance,
Jacob
Edit: I found a repair manual, going to hold off on ordering it just yet but I do see they are available. I was looking for something for one specific motor or motor series but I see they have one that's all Yamaha and Mercury outboards from 95 to 04.
Knee jerk reaction is the throttle position sensor is the issue but checking the resistance it seems to be linear although I don't anybody to help me so I have to move back and forth from the throttle to the motor which makes it a little harder to see if there are any jumps or anything anomalous.
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