Mercury 90 EFI losing power intermittently

[Montauk72]

I have a 2008 Mercury 90 EFI on my 170 Montauk. 4 times in the past two weeks when running at different speeds it feels as though the engine loses all power 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. Every time it has happened it has been within the first 5 minutes of running.

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 4 times in the past 300 miles.

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. The fuel line looks fine and the boat starts up immediately every time.

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

 

[woody66912]

Re: Mercury 90 EFI losing power intermittently

I have had three of these in the past two years, and what i found is that the fuel lift pump on the the valve cover would become overheated and lose pressure from 5 psi to 3 psi. Try this, when it dies off just let it be and pump the bulb if the rpms come back up then you know it's fuel. You can also get a pressure gauge and a tee fitting and install it on the fuel outlet of the pump, then you can run the hose though the rigging grommet and watch the pressure.

 

[Faztbullet]

Re: Mercury 90 EFI losing power intermittently

If you have the factory fuel line and its grey with red imprinted writing its bad so replace it. The inner liner degrades and stops up incoming fuel supply.

 

[Montauk72]

Re: Mercury 90 EFI losing power intermittently

I have had three of these in the past two years, and what i found is that the fuel lift pump on the the valve cover would become overheated and lose pressure from 5 psi to 3 psi. Try this, when it dies off just let it be and pump the bulb if the rpms come back up then you know it's fuel. You can also get a pressure gauge and a tee fitting and install it on the fuel outlet of the pump, then you can run the hose though the rigging grommet and watch the pressure.

Thanks for the reply, I don't have a bulb to pump but it seems likely that it is a fuel issue at this point

 

[Montauk72]

Re: Mercury 90 EFI losing power intermittently

Thanks for the reply. I do not have that fuel line. I just changed the fuel filters, not sure when they were changed last since I bought the boat used. Keeping fingers crossed that it is this easy of an issue to fix but doubt it. I also treated the fuel with Quickleen which was recommended.

 

[woody66912]

Re: Mercury 90 EFI losing power intermittently

Thanks for the reply, I don't have a bulb to pump but it seems likely that it is a fuel issue at this point

You could install one.