Fuel pump solenoid

R

Rick_D

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Joined
Jul 10, 2022
RO Number
34740
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I had a wire running from my oil pressure switch to my fuel pump just to get things up and running. Now I’d like to have the oil pressure switch go into a selonoid which will open a connection to the fuel pump on a thicker gauge wire. Can anyone recommend a selonoid switch to purchase?
 
Do you power your fuel pump directly from the oil pressure switch itself?…no solenoid or relay in between?
 
On my last boat, as per the instructions with my pump, I ran a wire from the + coil term ( purple ignition wire) to an oil pressure cutout switch, and then from the switch to the pump. It worked fine, but I didn’t love that the pump would not run until after the motor started. There were a few times I had to jump it to get the carb primed and motor started. that was a Facet pump, which drew only 1 amp.

i have not decided yet what I’m going to do with my current motor. For now I just have a wire running from the alternator ( purple ignition wire terminal) to the fuel pump. So the pump is running whenever the key is on. But the motor isn’t in the boat yet. I’ll most likely put in the oil pressure cutout before I drop the motor in. But with my 2 amp pump, I wasn’t planning on a relay or solenoid. From my understanding, the cutout switches are fine up to 5 amps, which is well above what my pump will ever draw. And my pump runs at about 7psi, which is a bit above what my carb wants, so my top concern now is whether or not to put a pressure regulator on. Holley says no, my carb guy says yes.

I still have the Mercruiser 30 amp relay from when this motor was mpi - i suppose that is an option as well.

86-865202T​

 
Last edited:
alk said:
On my last boat, as per the instructions with my pump, I ran a wire from the + coil term ( purple ignition wire) to an oil pressure cutout switch, and then from the switch to the pump. It worked fine, but I didn’t love that the pump would not run until after the motor started. There were a few times I had to jump it to get the carb primed and motor started. that was a Facet pump, which drew only 1 amp.

i have not decided yet what I’m going to do with my current motor. For now I just have a wire running from the alternator ( purple ignition wire terminal) to the fuel pump. So the pump is running whenever the key is on. But the motor isn’t in the boat yet. I’ll most likely put in the oil pressure cutout before I drop the motor in. But with my 2 amp pump, I wasn’t planning on a relay or solenoid. From my understanding, the cutout switches are fine up to 5 amps, which is well above what my pump will ever draw. And my pump runs at about 7psi, which is a bit above what my carb wants, so my top concern now is whether or not to put a pressure regulator on. Holley says no, my carb guy says yes.

I still have the Mercruiser 30 amp relay from when this motor was mpi - i suppose that is an option as well.

86-865202T​

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Thanks Alk. After your post I looked at what the pump pulls and it only pulls 1 amp. That would seem to be in the wheel house of the oil pressure switch so I think I will just have it directly wired to the oil pressure switch as it's such a low amp.
 
The way this is supposed to be done (if you follow Mercruiser's set up) is that the pump is powered off the R terminal on the starter solenoid when you are cranking it over and then when you release the key as the engine fires up the oil pressure switch powers it because now there is enough oil pressure to close the contacts. You do NOT want the pump powered anytime the ignition is on, because if the engine stalls and the needle valve in the carb leaks, you have created a bomb. Very dangerous and an insurance liability.
I would also use a relay to power the pump because those oil pressure switches are not really designed to carry all the current that the pump needs.
Head over to the Mercruiser I/O forum on iboats.com, someone posted the Merc wiring diagram on how to do this safely.
I still like my old engine with a carb and a mechanical fuel pump! The mechanical pumps last a very long time, are cheap to replace and are not affected by wiring connections getting loose or corroded, etc.
 

Wiring In Electric Fuel Pump

Hi everyone, I'm trying to incorporate an electric fuel pump into a 5.7 Mercruiser. The prior engine (5.0) had a mechanical fuel pump but the replacement engine does not have all of the holes for the mechanical fuel pump built into the block. Some notes: 1) The replacement engine is on an...
forums.iboats.com forums.iboats.com
here it is, some people here added a relay (called it a solenoid)
 
I would take a mechanical pump any day the week but these vortec engines don't have an access for mechanical anymore. I'll find out the number of amps the switch can provide and assuming it's well above what the pump pulls I'll do a direct wire between the two.
 
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Yep, hate my electric pump. The wiring, the sound of it, the failure potential, safety issues with the pump running when the engine is not. but with a gen 6 big block, there is no option to mount a mechanical pump.
 
cube relay and socket from a GM Blazer, any convenient ign switched power source,(coil,choke. etc)
pressure switch .The relay protects the pressure switch from the pump current
 
You need to have it setup so if the engine stops for any reason the fuel pump stops. That is the only safe way. The relay needs to be such that it cannot spark and cause an explosion. And you will be depending on the relay. It it fails the engine stops. So it needs to be a marine one not from a car or truck.

The one listed from Hardin Marine is not USCG meaning it may cause sparks.

For cars the fuel pump runs for 10 or 20 seconds when the ignition is first switched on and no oil pressure. Something like that would be ideal. If it was made for marine usage.
 
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