kammac

My 2001 Mercrusier 496 mag ho is wearing me out. It began by running great for 20 to 30 minutes than powered down. Changed cam shaft sensor, still same problem, changed low pressure pump. Still same issue. Installed new high pressure fuel pump still no change. Checked fuel pressure with new pumps and pressure is 34psi at idle. When I remove the vacuum hose from the regulator the pressure jumps to 42 psi. Once I start to accelerate the fuel pressure at the rail starts to drop down to 5 psi and the engine stalls. The only way to regain pressure is to remove the fuel line from the fuel tank where it connects to the low pressure pump. One note is when I remove the fuel line it makes a gasp sound like it is sucking air. I believe I have tried everything any help appreciated.

madbouyz

The only way to regain pressure is to remove the fuel line from the fuel tank where it connects to the low pressure pump. One note is when I remove the fuel line it makes a gasp sound like it is sucking air. I believe I have tried everything any help appreciated.

Based on the above the first thing that comes to mind is your fuel vent/breather line fitting on the hull has corroded shut .This is not uncommon at all but may not be your problem.
If it is , it's a cheap fix .

kammac

Thanks for the reply, I have removed the vent hose clean the vent on the hull, check the vent line hose, and the connection to the tank. Also tried to run with the gas cap off as well to vent. New Fuel line from tank to low pressure pump, new pickup line and new Barb fitting with out anti siphon. I am lost as to why it seems we are not venting properly!😬