2002 115 EFI Problems Fuel Pressure

I have a 2002 mercury 115 efi four stroke with 850 hours. It starts and idles perfect every time, once I get going for bout 10 min or so, it bogs down, looses power and white smoke/ steam comes out exhaust. I've pulled plugs, they're clean; did a compression test and it was fine, no more than 10 psi difference, and leak down test was good. Fuel pressure test was good at start up, left it on till loss power and pressure gauge would drop, prime bulb and pressure would come back to normal, but still had the white smoke/exhaust. Was also hearing a clicking sound from the low pressure fuel pump, and when i would prime bulb it would stop, so i replaced the low pressure fuel pump. Started up fine as usual, but after 10 min or so same thing, loss of power, white steam.....please help.