Donald
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Originally Posted By: DoubleWasp
Carb/electric fuel pump systems on boats work off of an oil pressure switch or from the alternator "tach" output.
Long story made short is, there is an extra stub on the starter that only turns on when the starter is being cranked. This powers the fuel pump during cranking. Once the engine is started, the tach output on the alternator is energizing the fuel pump relay. If the engine shuts down, the fuel pump stops along with the tach output.
The oil pressure switch arrangement works a little differently. A delay switch engages the fuel pump for 10 seconds, and then turns off. Once the engine develops oil pressure, the fuel pump relay is energized by the voltage going through the oil pressure switch. If the engine does, the fuel pump stops along with oil pressure.
Some manufacturers prefer the oil pressure system, because it will also shut down the engine in the case of oil pressure loss.
Problem is that the terminals on those oil pressure switches like to corrode, leaving a boat stranded.
I am pretty sure my alternator does not have a "tach" output. I cannot find any fuel pump relays with a timer that are marine quality.
Carb/electric fuel pump systems on boats work off of an oil pressure switch or from the alternator "tach" output.
Long story made short is, there is an extra stub on the starter that only turns on when the starter is being cranked. This powers the fuel pump during cranking. Once the engine is started, the tach output on the alternator is energizing the fuel pump relay. If the engine shuts down, the fuel pump stops along with the tach output.
The oil pressure switch arrangement works a little differently. A delay switch engages the fuel pump for 10 seconds, and then turns off. Once the engine develops oil pressure, the fuel pump relay is energized by the voltage going through the oil pressure switch. If the engine does, the fuel pump stops along with oil pressure.
Some manufacturers prefer the oil pressure system, because it will also shut down the engine in the case of oil pressure loss.
Problem is that the terminals on those oil pressure switches like to corrode, leaving a boat stranded.
I am pretty sure my alternator does not have a "tach" output. I cannot find any fuel pump relays with a timer that are marine quality.