Cool fuel system strange issue please help

[Iaintslow]

7.4 mpi with cool fuel system
Boat suddenly died while cruising. Testes fuel pressure and it was 0. Installed new pump and still pressure 0. Checked old pump and it was working whiled disconnected so it was never bad. So i took out my new pump again and tested it while its disconnected from fuel lines and it works. Now im completely confused i installed new pump back again and it did prime with key on and pressure in the rail went up. I started the engine and pressure start dropping and engine died again. After that pump not primping anymore and i checked voltage is fine. Looks like it will only prime again and work for a sec after i disconnect feed line and release fuel. Is something clogging input side and pump stops after curtain pressure is reached or something?

 

[QBhoy]

Check the relay.

 

[Iaintslow]

Check the relay.

I checked wire and i do get voltage when key is turned on but pump wont prime, i dont think there is relay looks like power comes from ecu directly

 

[tpenfield]

Pressure regulator ?

 

[alldodge]

I checked wire and i do get voltage when key is turned on but pump wont prime, i dont think there is relay looks like power comes from ecu directly

The pump runs but no fuel making it to the pump. This would be a restriction with the tank pickup, antisiphon valve, fuel filter or the line is clogged or collapsed. In most cases its the fuel tank tube or antisiphon valve.

Start with removing the fuel filter and dump contents into a clear container, see if there is only clean gas. Also note the level of the gas in the filter when removed. Install new filter

Remove fuel line from tank, then remove the antisiphon valve which is the barbed fitting the line was attached to. See if its has gunk in it and that its easy to blow thru in one direction and not the other (very low air pressure). Blow thru the tank tube to see if you can hear bubbles in the tank.

Inspect fuel line going to filter and if clear and clean, attach another longer fuel line piece and use a portable gas can and place line in can.

Turn key on and see if pump will prime, and bleed air out of line at Shrader valve

You have not mention your engine serial number, but the ECM applies a ground to the relay to energize it. When relay is energized it transfers power

 

[Iaintslow]

The pump runs but no fuel making it to the pump. This would be a restriction with the tank pickup, antisiphon valve, fuel filter or the line is clogged or collapsed. In most cases its the fuel tank tube or antisiphon valve.

Start with removing the fuel filter and dump contents into a clear container, see if there is only clean gas. Also note the level of the gas in the filter when removed. Install new filter

Remove fuel line from tank, then remove the antisiphon valve which is the barbed fitting the line was attached to. See if its has gunk in it and that its easy to blow thru in one direction and not the other (very low air pressure). Blow thru the tank tube to see if you can hear bubbles in the tank.

Inspect fuel line going to filter and if clear and clean, attach another longer fuel line piece and use a portable gas can and place line in can.

Turn key on and see if pump will prime, and bleed air out of line at Shrader valve

You have not mention your engine serial number, but the ECM applies a ground to the relay to energize it. When relay is energized it transfers power

Where is fuel pump relay located? Pump only primes once and then does not turn on at all after that. If i take it out it turn on again. Putt it back it primes ones ( i get fuel in the rail enough to start the engine) and then stops working again
Serial number 0L682512
I just chaged fuel filter and cleaned pick up line btw 2 days before this happened. Boat ran fine for these 2 days.

 

[Bt Doctur]

unplug the pump and hot wire the connection , see if motor runs.
ecm provides the ground for the relay to operate the pump

 

[Bt Doctur]

click to enlarge

 

[alldodge]

Where is fuel pump relay located?

Remove the top plastic cover and there will be 2 square relays fastened to a metal bracket. One is fuel pump and the other is main power and they are both the same and can be swapped.

Pump only primes once and then does not turn on at all after that.

This changes things a bit, because the ECM turns the pump ON for couple seconds when key is first turned ON. Do not go do the rest of the things I said previously.

When key is turned to ON, the pump should prime and it does.
The pump gets turned back ON only after the ECM sees that the distributor is firing. When cranking, you should see the tachometer moving up to around 300 RPM, Does it move up?

If i take it out it turn on again. Putt it back it primes ones

You have to remove the fuel pump to get it turn turn ON again?
The fuel pump does not turn ON again if you turn key OFF and then turn back ON?