Can I power up elec. fuel pumps from coil?
04-25-2007, 06:42 AM
#11
Bad Dog's setup is good BUT.
You also gotta jump to the starter circuit for auto priming. Otherwise, you gotta remember to prime.
SPDT relay.
Center post to fuel pump (appropriately fused for pump).
N/O post to starter solenoid output.
N/C post to 12v bus (30A fused).
One side of relay coil to ignition "run" position (ignition coil 12v+).
Other side of relay coil to oil pressure switch (N/C 10psi oil pressure switch).
When ignition switch moves to ON position, low oil pressure allows ground path to be complete to close the relay. With relay closed, fuel pump can only receive power when ignition switch is in the START position (solenoid energized). After oil pressure rises, relay drops open, passing current from 12v bus to pump.
If engine stalls, oil pressure drops, pump stops.
It's also extra good sense to have an accessible pump master switch that kills juice to the entire pump circuit in the event of some malfunction.
You also gotta jump to the starter circuit for auto priming. Otherwise, you gotta remember to prime.
SPDT relay.
Center post to fuel pump (appropriately fused for pump).
N/O post to starter solenoid output.
N/C post to 12v bus (30A fused).
One side of relay coil to ignition "run" position (ignition coil 12v+).
Other side of relay coil to oil pressure switch (N/C 10psi oil pressure switch).
When ignition switch moves to ON position, low oil pressure allows ground path to be complete to close the relay. With relay closed, fuel pump can only receive power when ignition switch is in the START position (solenoid energized). After oil pressure rises, relay drops open, passing current from 12v bus to pump.
If engine stalls, oil pressure drops, pump stops.
It's also extra good sense to have an accessible pump master switch that kills juice to the entire pump circuit in the event of some malfunction.
04-25-2007, 07:10 AM
#12
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My 525sc's have both mech and electric fuel pumps, on my maiden voyage I was watching the fuel pressure guages closely one stayed at 8psi the other 7 psi running on just mechanical pumps. What is the proper psi that I should be looking for? Should I be running the electric all the time? I did turn them on when I brought the rpms up to 4000 and they seemed to boost press to about 9-10 lbs.
After reading the above I'm thinking that I should just wire them in as Mcollinstn said and then I don't have to think about it anymore. Blowers are new to me, just learning.
After reading the above I'm thinking that I should just wire them in as Mcollinstn said and then I don't have to think about it anymore. Blowers are new to me, just learning.
04-25-2007, 09:59 AM
#13
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For anyone running a merc efi motor with bigger than stock fuel pump, there is a 10 amp fused relay that turns the fuel pump on,I used the power from that to trigger a 50 amp bosch relay that is wired directly to the battery with 10 gauge wire as the wire is tiny 14 gauge stuff and barely supplys enough power for a stock electric pump,had voltage drop issues 6 years ago trying to run aeromotives fuel pump that procharger originally supplied to replace the oem pump,this is a common problem,Smitty
04-25-2007, 06:39 PM
#14
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Location: Eastern Lake Ontario, NY
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i cant get my oil pressure sender to work. And if it is normally closed and you give it power on one side wont it automatically be pushing power out the other? Would you want a normally open until it has pressure and then it closes the circuit and trips the relay to turn on the fuel pump. Can i temporaly use a relay and have my coil trip the relay to have my pump turn on. Just till i get the oil pressure sender working?
