Not holding fuel pressure

[Jon4mitch]

I have a 2003 speedster mercury v6, 240hp EFI that’s not holding fuel pressure. When I turn key to “on” position, I get 41 PSI, then drops right to 10 instantly. Boat runs great on land, dies when in water when I give it gas. Compression is 135 across all 6 cylinders. PLEASE HELP!!!

 

[raalost]

Hi there, any chance you found a solution for this issue? I have the exact same problem and have taken the jet to every marine mechanic in the country with absolutely no fix…. starting to lose hope and no one can tell me why the boat is working on land but switches off as soon as it gets in contact with the water!

 

[rusty nail]

there is a dedicated mercury boats forum and you may have more success posting your questions there.

 

[Tim75]

Hi there, any chance you found a solution for this issue? I have the exact same problem and have taken the jet to every marine mechanic in the country with absolutely no fix…. starting to lose hope and no one can tell me why the boat is working on land but switches off as soon as it gets in contact with the water!

Fuel pressure should be 34-36psi whether engine is running or not. And should be steady. When the key is turned OFF, it should take several seconds to a minute for the pressure to drop.

Typical leak point are the injector(s) themselves. Any fuel hose in the pressure side. The fuel rail (plastic). Bad o-rings. There are about a dozen. Bad pressure regulator.

Injectors can be serviced for about $25 each after they are removed. $750 for a set from Mercury. Don't waste your time and money on pour-in-the-tank cleaners.