mercruiser fuel pump efi

[festamb1]

Hi i got my boat out on the inland river last week and gave it a test run as it has been out of the water for a year now, everything was fine for about 40 minutes until the engine cut out for no reason whilst going down the river i am inland so only going around 5 knots.
once i got moored up i checked the engine to find that the electric fuel pump was not working so after some check i fitted a fly lead on the pump and it started up first time and i managed to get it back on my mooring can somebody tell my what would stop the pump working as i had no waring at all my enging is a 5.0 v8 efi 1998 model.
the gearlube looks fine can this be linked out to rule out that its not a problem with that and if it is the oil presure switch would i get any indecation from the warning buzzer.
i have put the pump wiring back on now and i dont get the 2 second pump run when i put the ignition on now any ideas what holding it out as my oil pressure on my gauge was fine when the engine was running.
many thanks

 

[Scott Danforth]

if you could hot-wire the pump to get you pressure. its not the pump

you could have a bad oil pressure switch or a bad relay or bad connection

 

[Furbird]

Depending on the setup, most have two oil pressure senders; one for the gauge and one for the pump. If the pump one has failed, that could cause your problem.

 

[festamb1]

I have ordered a new oil pressure switch which should turn up soon would this stop the pump from coming on for the 2 seconds when you put the ignition on as i have lost this, the pump is fine as when it was hot wired the boat run fine by the looks of things the oil pressure switch looks like it cuts off the earth when in fault.

 

[muc]

Oil pressure has nothing to do with the fuel pump on your EFI engine.
The fuel pump relay gets its ground from the ECM.
Suggest you get a copy of the wiring diagram and see if you have power and ground where you should.
Remove, clean and reinstall the ECM grounds on the flywheel cover.

 

[festamb1]

muc
i have looked at the diagramme and the earth comes from the oil pressure switch and the gear lub float i tested it all yesterday this is how it cuts out the fuel pump if something goes in to fault on the boat.
i connected up a fly lead so a seperate earth and pump works fine.

Many Thanks

 

[muc]

You didn’t post a serial number so I can only talk about MerCruiser EFI engines in general, but.

There is a fuel pump and a fuel pump relay. The fuel pump gets its ground through the rest of the ground wires. It gets its power through the fuel pump relay. The relay gets its ground through the ECM and its power through a fuse.

NO fuel injected engine has ever been produced by MerCruiser that cuts out the fuel pump when a sensor fails.

You and the other posters may be getting confused by the difference between how a MerCruiser carb engine vs a EFI engine work. On EFI engines a failure of the gear lube or oil pressure switches can turn on the warning horn and decrease power output of the engine. But not turn off the engine.

 

[festamb1]

Hi Muc my serial number for my engine is OL089340 i have lost my earth to my fuel pump so i checked the oil pressure swith and there is no continuity to earth so i checked the earth on my fuel pump and this was also missing so i ran a fly lead to an earthing point and the pump comes on as it is meant to do you know of a reason to lose my earth as you are correct it runs through my ecm.
Do i need this ecm earth could i not just run a new earth to my fuel pump as the power side of it is still through the fuel pump relay and will still turn the pump on and off as it should.

Many Thanks

 

[festamb1]

This the wiring for my engine

 

[muc]

Thanks for the serial number. It looks like you have a MEFI 1 ECM with a cool fuel 2 fuel system.
I also noticed that this engine has not been registered with MerCruiser. This could be a problem because the owner would not have been notified of of any required updates. Suggest you contact MerCruiser and get.this registered in your name.

I’m a little confused about your comment that the oil pressure switch is missing it’s earth. This should be a one wire switch, so it gets it’s earth where it screws into the engine block. The one wire will trigger the warning horn.

If we are talking about the fuel pump earth and not the fuel pump relay. Yes you could add an extra earth wire. But I would recommend against that because all the earth wires connect together and connect to the stud on the flywheel cover. If you have one bad earth you could have others. When a engine has faulty earth connections the electricity will try to find an alternate path to ground. This can cause problems on any engines but can cause real trouble on a EFI engine.

The fuel pump doesn't get its earth through the ECM, the fuel pump relay does.

​​​​​​​I suggest you completely disassemble and clean the earth stud on the flywheel cover. This is number 2 in box C on the wiring diagram you posted.

 

[festamb1]

Hi Muc

Thanks for your reply i did clean up the earthing stud and all of the connectors about three months ago so i know this is good so are you still sure that there is nothing that goes into fault that holds my fuel pump out as it now looks like i just have a bad earth to the pump now.
The comment about no earth on the oil switch is i test the ternimal on my old switch and there was no continuity with the engine not running where as my new switch has continuity from the body of the switch to the ternimal.
I thought this was my earth fault on my fuel pump as i was always told that my oil pressure switch would swith my pump off if i lost oil pressure or my gear lube bottle got too low.

Many Thanks
Muc

 

[muc]

There is nothing in the ECM that removes the ground for the fuel pump.
When MerCruiser uses an oil pressure switch for the fuel pump (on carb engines only) they use it to control the power. Not the ground.

If your fuel fuel pump is missing the ground, the problem is in the wiring harness.

 

[festamb1]

Many Thanks Muc

You sure no your stuff