150 Optimax no start

[lpugh]

Update. Bypassed low pressure pump by disconnecting wires, plugging low press pump output, and plugged VST top vent. Hooked fuel tank directly to the top hose removed from low pressure output. Motor starts and runs without even pumping primer bulb while running. . Fuel pressure 86psi, air 78-80psi. Then hooked fuel tank directly to bottom[input] side of low pressure pump, no start or run. Local auto parts store had China copy of Merc pump, no difference. Checked voltage into low pressure pump, and checked pump coming on. Any possibility other than $400+ low pressure pump from Merc?

Check voltage across the two wires to the pump, while the pump is running, should be with in 10% of battery voltage. resistance in the driver side would have the same effect as low voltage on the power side. Checking from battery ground to pump ground voltage should be less than one volt with pump running and pumping fuel. Don't want replace the pump and then discover you have a driver side issue

I have seen very rare exceptions to this and I am sure Don will jump in and correct me if I an wrong about this, Keep in mind I am a Auto Tech not a marine tech. Just stressing that the ground side is of equal importance to the power side

[EuropeanAM]

I concur- and if your voltage tests indicate proper/adequate voltage, obtain the CORRECT pump and install it.