Thanks for all your advice, especially BUP who always chime in with invaluable help to us 496 owners who is more or less desperate for some good advice. I have learned a lot reading your posts!

Got the engine running by using a primer bulb connected to an outboard tank. It fired right up and ran like normal. Fuel pressure when fuel pump running before cranking was 40 PSI and after start around 38PSI and while revving it up to 2500RPM it went down to 36PSI. Then I put the fuel hose back to the boats normal tank and started it up again. I was expecting it to stall but it ran like normal with the same fuel pressure. Fuel pressure seems to be on the lower side and I´m worried that it could lead to a lean condition while under load. After these tests, for the first time since new I opened up the fuel filter in the fuel cool pump. It was kind of blackish at the bottom but looked almost like new on ap 1/3 of it. No debris or water other than the blackish color. The cool fuel pump I have is a gen 3, the water/fuel sep filter that I mentioned earlier has been in the boat since I had my old 330/7,4L in it. The serial # is correct even if it seems to missing in the Merc system. Now I wonder if the best thing is to change both the high and low pressure pump while I´m on it or just test again with new fuel filter? Would it be a risk to test it under load in water? What is the board´s opinion?

I just thought I tell how my problem with the fuel pump was solved. I took the decision to change both high and low pressure pumps and after that the fuel pressure was back to normal again so I don´t know which of the pumps was causing the problem. I noticed that there were no signs of color flakes in my fuel pump after 550 hours, looked as new inside. It was a little tricky to get the pumps in the right position when putting the lid on, otherwise it was a easy job.

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