Logo
FULL SITE MENU

electric fuel pump

A standard electric fuel pump set up for a carbed mecruiser is wired a specific way.

There is a oil pressure switch (ITEM 8) attached at the oil sender location, This switch has the (run) purple wire passing thru it (normally open contacts) so if the motor looses oil pressure or the motor is shut off the pump shuts off. The prssure switch can be purchase from merc and a additional or different fitting installed at the pressure sender to mount the pressure switch.

There also has to be a connection to the 12 volt ignition on (purple) wire from the starter solenoid so when cranking the engine over the fuel pump gets 12 volts at that time. below is a typical merc schematic for reference. it is from a V6 wiring diagram but it would be wired the same.

What fuel pump you choose just make sure it is Marine grade!!!!!!!
 
As for a fire hazard with an Electric Marine fuel pump........ I don't see any more hazard than what fuel itself poses in an engine bay. There are literally thousands and thousands of these electric fuel pumps in use. In fact, the newer GM engines are not even machined for the mechanical fuel pumps.
Just use a USCG approved electric fuel pump, and you'll be OK.
A common lower pressure carburetor fuel pump is the Carter.


As Kghost says, the N/O (normally open) oil pressure switch must be in the loop, and he explains why.

However, to keep the pump's amp load from the Ignition circuit (typically a small load circuit), we can power the fuel pump via a relay, allowing the lower amperage ignition circuit to trigger the low current side of the relay only.
The higher load side of the relay would be independantly powered, and in turn will power the fuel pump.
A relay is very simple to incorporate.

Along with this, comes the need for what's referred to as a "start-by-pass" circuit, in order to operate the fuel pump prior to engine oil pressure.

As for the start-by-pass circuit, this is pulled from the solenoid side of the starter motor circuit.
It will drop out once the key "start position" is released.
At this point, the N/O oil pressure switch will close and will continue pump operation.

There's an alternate to the start-by-pass, if interested.
That would be a helm located momentary switch in lieu of the start-by-pass circuit. This allows for fuel pump operation prior to any engine cranking. Push a botton or move a toggle switch, and you have fuel pump operation.
The benefits are: no unnecessary cranking prior to fuel delivery, no unnecessary battery drain, and to some degree, this will even extend starter motor life!

Whether the start-by-pass is used, or the helm located momentary switch is used, either can trigger the relay.

NOTE: if the helm switch is used, it must be a momentary switch in order to satisfy the USCG regs.





.
 
Last edited:
RicardoMarine said:
There's an alternate to the start-by-pass, if interested.
That would be a helm located momentary switch in lieu of the start-by-pass circuit. This allows for fuel pump operation prior to any engine cranking. Push a botton or move a toggle switch, and you have fuel pump operation.
The benefits are: no unnecessary cranking prior to fuel delivery, no unnecessary battery drain, and to some degree, this will even extend starter motor life!
Click to expand...
I like this idea, but how would one plumb in the pump if leaving the mechanical pump?
If in series, does fuel flow freely through these electric pumps when not in use? it would have to for that to work.
Or would I run this pump parallel to the mechanical pump?
If the latter, I assume I would need two check valves (or 1 shuttle valve) to resolve the positive output from either pump to the carb. so the pump in use doesn't push backwards through the one not in use (path of least resistance), or maybe my anti siphon at the tank would ensure that doesn't happen.
I have lots of shuttle valves for hydraulics, but doubt they are fuel approved.
 
I'll take a stab at this for you......

hystat said:
I like this idea, but how would one plumb in the pump if leaving the mechanical pump?
Most who end up going to the electric fuel pump, remove the mechanical, and block the opening off. Some mounting kits even use the mechanical pump bolt pattern.


If in series, does fuel flow freely through these electric pumps when not in use?
I believe that these are rotary vane type pumps, and may not flow as with the mechanical pumps.
I've not tried this, so I really can't answer that!

it would have to for that to work.
If in series, and if the electric pump was the "ride along" pump, then yes, it would need to be!
But again, I don't know whether one would free flow or not.


Or would I run this pump parallel to the mechanical pump?
Again, by the time that the electric pump is considered, the mechanical pump is ready to be abandoned.


If the latter, I assume I would need two check valves (or 1 shuttle valve) to resolve the positive output from either pump to the carb. so the pump in use doesn't push backwards through the one not in use (path of least resistance), or maybe my anti siphon at the tank would ensure that doesn't happen.
I have lots of shuttle valves for hydraulics, but doubt they are fuel approved.
If we get into valving, we also get into areas that may not conform to USCG regs.
These regs (regarding gasoline) can be rather complicated and long drawn out. I've read them before, and you have to dig rather deep for certain criteria.
I'm sure that you could find it..... but be ready for a long read.
Click to expand...
 
I bought this boat used and it is a 1981 Formula F18 with a 305 chev engine. I rebuilt the carb and found water in the fuel bowl area of the carb and the jets were corded up, I can imagine what the fuel pump looks like. I want to replace it before ice off and fishing starts. The external fuel bowl on the fuel pump is empty but you can see it has been there a long time. Just thought I would be proactive instead of reactive and not need to be towed to back to the dock. I fish mainly by myself.
 
Sooner5151 said:
I bought this boat used and it is a 1981 Formula F18 with a 305 chev engine. I rebuilt the carb and found water in the fuel bowl area of the carb and the jets were corded up, I can imagine what the fuel pump looks like. I want to replace it before ice off and fishing starts. The external fuel bowl on the fuel pump is empty but you can see it has been there a long time. Just thought I would be proactive instead of reactive and not need to be towed to back to the dock. I fish mainly by myself.
Click to expand...

Ayuh,.... The quick, easy, simple, 'n probably most Reliable thing to do is, Replace what's There....

Ya got a canister filter before the fuel pump, Right,..??
If not,... Add 1....
 
yes, I do have the canister filter. I pulled the castiron exhaust off and am cleaning them up due to my budget says I will have to use them at least another year. Got any good ideas for the gasket for the caps and 90degs turn downs. I will also need to replace one of the water hoses due to I had to cut it off. The hoses were stuck on pretty hard. Thank you.
 
Sooner5151 said:
yes, I do have the canister filter. I pulled the castiron exhaust off and am cleaning them up due to my budget says I will have to use them at least another year. Got any good ideas for the gasket for the caps and 90degs turn downs. I will also need to replace one of the water hoses due to I had to cut it off. The hoses were stuck on pretty hard. Thank you.
Click to expand...

Ayuh,... Oem replacements is the Best, 'n in My mind, the Only way to go...
 
Back
Top