Mercury 90 FourStroke EFI intermittent loss of power

by Dave

I have a 2008 Mercury 90 EFI on my 170 Montauk. 4 times in the past two weeks the engine loses all power but within the first 5-10 minutes but still stays running. During the loss of power, even if I open it all full throttle it sounds as though it is not getting fuel and the rpms stay low. No warning alarms go off. The engine also runs very rough during the episode but quickly recovers. The interesting thing is that it starts right up reaches top end for 10 seconds or so then this occurs.

By shutting the boat off and restarting it or bringing the throttle all the way down it seems to fix it and the boat runs perfectly. As I said it has only happened 5 times in the past 300 miles. Top end speed is the same after issue resolves.

The gas is always fresh and the boat is run approximately 100-150 miles a week. Other than this intermittent issue, it runs great and feels and seems like a new engine.

It seems similar to how my old 2008 40 hp EFI felt when I lost a coil pack twice however the only difference is that this quickly resumes normal operation.

I spoke to the mechanic who does my work and he told me that it would be very difficult to diagnose until it goes completely. I am at a loss since I am basically being told that a breakdown is inevitable.

Any ideas or suggestions for me to look into is greatly appreciated, thanks