Help me understand wiring

[MCL]

Hi

Im trying to wire a electric fuel pump.I have connected the oil pressure switch no prob.But what I dont understand is that you are supposed take electricity from the starter solenoid to power the fuel pump when cranking(no oil pressure/low).So both a wire from the pressure switch and starter solenoid will be connected to one terminal on the fuel pump,my sense tells me that when the oil pressure switch open,it will also supply the starter solenoid electricity while the engine is running,and that cant be good.

From which wire should I take current to power the fuel pump during startup.

 

[Bt Doctur]

Re: Help me understand wiring

The "R" post

 

[MCL]

Re: Help me understand wiring

My starter only has 3 terminals.One has 2 red wires and a orange.Then there is the solenoid terminal with a yellow/red wire and a terminal with a black wire that goes straight into the starter itself.

The stater is new.The last owner bought it.I suspect it might be a car starter as marine parts are hard and expensive here(Finland).

 

[Bt Doctur]

Re: Help me understand wiring

Post a pic of it of you can.
You can install a "priming button" .Most times I install elec pumps I add a on-off-monentary on switch on th eengine.. Should the pressure switch fail you use the "on" position to supply fuel. When changing filters, after a long layaway, etc use the momentary position to prime the system.

 

[bruceb58]

Re: Help me understand wiring

You need the 4 wire starter terminal to do what you exactly want to do...but...since you don't have one(The R terminal in the picture above), run a wire instead from the terminal that engages the solenoid(S terminal) through a diode to the fuel pump and that will accomplish the same thing. You have to make sure the diode's current rating is above what the fuel pump demands.

 

[sasto]

Re: Help me understand wiring

Post a pic of it of you can.
You can install a "priming button" .Most times I install elec pumps I add a on-off-monentary on switch on th eengine.. Should the pressure switch fail you use the "on" position to supply fuel. When changing filters, after a long layaway, etc use the momentary position to prime the system.

If she were mine I would do exactally what Bt. Dr. says.

 

[MCL]

Re: Help me understand wiring

I can get a picture of the starter tomorrow.My dilemma is,that if I rob power from the starter solenoid for the fuel pump during starting,wont the current from the oil pressure switch also power the solenoid when ther is oil pressure.

There are 2 red wires and orange wire to the main terminal on the starter.Then there is the yellow-red wire that supply the starter solenoid power during startup.Should I connect the yellow-purple wire from the fuel pump directly to the solenoid terminal.It doesnt sound right.

 

[Don S]

Re: Help me understand wiring

Your main problem is, you don't understand how the solenoid works. It is designed so it will put power to the fuel pump, Years ago with points distributors, that terminal was for full power to the point during cranking.
Mercruiser has been building them that way for many years now, no need for you to get carried away with worries about the pump pulling power away from the solenoid. There isn't enought power there to even worry about.
Here is a drawing from the Mercruiser service manual (I added the name tags only) to show the wiring of an electric fuel pump.

 

[bruceb58]

Re: Help me understand wiring

Don,

I think his starter solenoid doesn't have the terminal that was used to supply the points during cranking. Thats why I was suggesting using the start terminal itself(or output of the start slave solenoid) and going through a diode.

 

[Don S]

Re: Help me understand wiring

I think his starter solenoid doesn't have the terminal that was used to supply the points during cranking.

Then it's probably an automotive starter, and not marine.

Of course if it is a cheap aftermarket marine starter that doesn't have that terminal, it could still be used by wiring the purple yellow wire to the slave solenoids B terminal instead of the starter solenoid.

 

[MCL]

Re: Help me understand wiring

Im back but with no pictures.Took some with my new phone but I lack the cable to transfer them to my computer.

I doublechecked and there are only 3 terminals on the starter,some of the starter is unpainted aluminum and rest is zinced steel.It seems its safe to say its a carb starter.We dont have the marine parts availability like you do over there,I still want to use car starter,it starts the engine fine.I just got a new johnson ultima bilge pump to keep the bilge dry,do I run a big risk with corrosion issues with the car starter?As for the fuel pump wiring I will wire the oil pressure switch and a prime button(like btdoctur).I like to keep things manual anyways.

 

[sasto]

Re: Help me understand wiring

We dont have the marine parts availability like you do over there,I still want to use car starter,it starts the engine fine.

Are you in DR?....PR?.....careful, my friend.

 

[bruceb58]

Re: Help me understand wiring

Of course if it is a cheap aftermarket marine starter that doesn't have that terminal, it could still be used by wiring the purple yellow wire to the slave solenoids B terminal instead of the starter solenoid.

Can't do that without a diode unless you want the starter to engage once oil pressure comes up. Need a diode in there.

 

[bruceb58]

Re: Help me understand wiring

do I run a big risk with corrosion issues with the car starter?

No...you run the risk of blowing yourself up.

 

[MCL]

Re: Help me understand wiring

Could you be more specific.I know that carbs and fuel pumps are marine specific.

The starter looks exactly like this one

 

[Simoniz]

Re: Help me understand wiring

Marine starters and alternators have the solonoids and brushes sealed so that any sparks created there cannot ignite a build up of petrol / gas vapour, should it be present.

In a car application, the engine is well ventilated but a boat engine sits in a poorly ventilated engine bay and petrol vapour, being heavier than air, will accumulate low in the engine bay, where the starter sits.

Thus automotive starters have no need for the electrical contacts and brushes to be sealed.

 

[Don S]

Re: Help me understand wiring

Can't do that without a diode unless you want the starter to engage once oil pressure comes up. Need a diode in there.

Good point, missed that completely :redface:

 

[MCL]

Re: Help me understand wiring

Marine starters and alternators have the solonoids and brushes sealed so that any sparks created there cannot ignite a build up of petrol / gas vapour, should it be present.

In a car application, the engine is well ventilated but a boat engine sits in a poorly ventilated engine bay and petrol vapour, being heavier than air, will accumulate low in the engine bay, where the starter sits.

Thus automotive starters have no need for the electrical contacts and brushes to be sealed.

Thank you.

I will check the construction of the starter to be on the safe side.But if I remember correct only the terminals are on the outside and they have rubber caps on them.Everything else is packed inside with no vents.It just lacks the terminal for the fuel pump.

It reads somewhere on the boat to use the vent before starting and below cruising speed.