fuel pump well not shut off

[tracker14437]

2006 Mercury 150 hp DFI fuel pump inside vapor separator well not shut off

 

[alldodge]

Looking at the wiring diagram I would think your main power relay (MPR) contacts are stuck. The MPR is item 39

http://162.144.28.33/lib/mercury/manuals/135-150.html#/138

This is how I "think" the MPR is controlled

Red - battery power
Red/White - power to fuel pumps
Purple - Ignition key (one side of relay coil)
Yellow/purple - ground supplied by ECM (other side of relay coil)

 

[tracker14437]

I have replaced the main power relay twice which only seems to solve the problem for a couple times out with the boat.

 

[alldodge]

I have replaced the main power relay twice which only seems to solve the problem for a couple times out with the boat.

Check the wiring from the relay coil to the ECM and plug contacts. Guessing that it may not be burning out the relay, thinking there is something which is creating a ground that keeps the relay energized. Replacing the relay and moving the contacts may be breaking this contact for a short time

Assuming the fuel pump runs but the motor does stop

 

[tracker14437]

Ok...I spent the whole day Sunday checking all the wires, cleaning all the terminals and engine block and all of the positive wires I could take off. I also disassembled the VSC, cleaned all the screens and filters, checked plugs going to fuel pump...everything seemed good.We took the boat out last night; started right up and ran great. Shut boat down to fish and fuel pump still wouldn't shut off. Is there a pressure switch built into the fuel pump that shuts down so relay disconnects or what sends the signal for everything to shut down.I would greatly appreciate any advice you can give me.

 

[alldodge]

Is there a pressure switch built into the fuel pump that shuts down so relay disconnects or what sends the signal for everything to shut down.

None that I am aware of. The ECM applies a ground to one side of the relay to turn it ON. Somehow that ground is not being disconnected.

I think you need the ECM tested for this issue and find out of its the ECM or something else causing it. The problem is I don't know of anyone which does test them, but hope there is someone (I'm a I/O and inboard guy)

If you place a probe from a digital voltmeter on the lead from the relay coil going to the ECM you can tell if the ground is being applied or removed. There is 12V applied full time to one side of the coil relay. So if the meter is placed on the other side of the coil, you should see 12V until a ground is applied. So if you see 12V then the relay should not be energized.

Now if the only issue is the relay staying connected, you could place a switch in the line. Leave it connected until shutting the motor down and if pump stays ON, flip the switch OFF. Reconnect when you want to fire back up