2010 Mercury 90HP EFI 4 stroke - Bogs down after running short time

[Aldo1]

This engine was bought new in December 2010 (on a 21' pontoon) so this summer is our first use. The engine starts easy and runs smooth. No smoking or roughness. When I first throttle it up to full, I reach 5500-6000 RPM pretty quick and the boat flies, but after a short period of time (<10 minutes) the most I can get is 4000-4500 RPM (and a considerable loss of speed). When I slow to idle, it still runs very smooth and no smoke. It seems like it runs best when it is cold and bogs down after warming up.

I have had a cavitation problem when we have gone through wakes, but I wouldnt think that would cause the engine speed to drop (in fact just the opposite?

Welcome any ideas / suggestions.

 

[Texasmark]

Re: 2010 Mercury 90HP EFI 4 stroke - Bogs down after running short time

Squeeze the fuel primer bulb when it bogs down. If it recovers, your fuel tank vent may not be working. On an engine that new one wouldn't expect any big problems that one usually has to address on older engines. Get back with your answer and we will go from there.

Mark

 

[Aldo1]

Re: 2010 Mercury 90HP EFI 4 stroke - Bogs down after running short time

This sounds really stupid, but I dont think it has a primer bulb. I know what you are talking about and I have this problem with my 9.8HP Merc, but this has an electric pump that feeds the engine. I don't think there is any bulb (at least I have never seen one). Also the tank is a a large fixed tank with and outside fill cap - I think the fill cap acts as the vent as well. (again, I have had this on my small engine and portable tank. Actually with the small engine, when the bulb collects air or the vent isnt open on the tank it completely stops running.)

On the 90HP it continues to run, seemingly unchanged - except I cannot get it to run at a higher RPM.

I was thinking maybe this was a choke problem. The problem only occurs after it is warmed up. But with the EFI I am not sure that this is something I can adjust. It may be a computer glitch or a temp sensor malfunction that is not sending the signal to the computer to let in more air. But I would have thought I would smell rich exhaust and rough idling but I havent noticed it.

 

[Texasmark]

Re: 2010 Mercury 90HP EFI 4 stroke - Bogs down after running short time

Possibly your current is so large that it acts differently than your 9.8 did, or the vent is partially blocked...removing the fill cap for a test would answer that and last, yes electronics could be your problem as they can fail at different temperatures and act normally at others. I had a CDM on my current engine go bad just the opposite....failed till warmed up. When I was in the business, we used Freeze Mist to locate thermal problematic components. Using it would be a little tricky considering your application.

Mark