02 Mercury 225 Optimax Fuel/air Issue!

[Boatrescue]

Have a 02 Optimax that won't run because of a fuel air issue. I have 80 lbs fuel and 85 lbs air pressure. Replaced both high and low electric fuel pumps, manual pump, both tracker diaphragms and for diaphragm and also swapped both fuel rails off a running motor still no difference. Any suggestions would be greatly appreciated.

Also if release some air pressure off the air valve it will try to start.

[EuropeanAM]

This engine would be a 3L model, so I will move it to the 3L Forum for you.

Please take a moment to read the Announcements at the top of that forum, and be sure to provide the Required Info (serial number) when posting. Thanks!

The engine will never run this way.

When you are cranking it, does it take about 15-20 seconds longer for fuel pressure to build, or does it instantly come up with the air pressure?

Make sure there is actually fuel IN the VST. An empty VST will do precisely what you've described.

[Boatrescue]

It takes a moment to build fuel pressure

[Boatrescue]

Also a lot of air in the fuel

[lpugh]

Is the seal in place and good that goes on top of the high-pressure pump that seals it to the vst top for the fuel outlet?

[EuropeanAM]

If the fuel pressure is not climbing instantly to 10 psi over AIR, you have a HP fuel delivery problem.

Theres a small passage in the HP pump chamber that helps deliver fuel for the HP fuel pump. If this passage is plugged, the HP pump has nothing to deliver and you end up with only pressurized air in the fuel side, perhaps a few drizzles of fuel.

This passage is a straight-shot across the front chamber from a PLUG they installed to access and machine the hole. Only mention this to help you envision where the passage I'm suggesting is located.