Electric fuel pump for Mercruiser

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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.
 
If you are going to do the oil pressure switch, I suggest Caterpillar switches. They are rugged as a rock and very rarely fail.

Also, you'll need to add a thumb button on the dash to to make the electric pump run long enough to make sure you have a prime if the boat has been sitting a long time.

Or, you will have to manually fill the float bowl through the vent (which does not work on most marine carbs, they face down) so the engine will run long enough to get oil pressure which will then keep the fuel pump running as long as the engine runs...
 
Ok, electric fuel pump and wiring out, new mechanical fuel pump in, runs great. The old mechanical was broken and was not replaced last August like I was told. Push rod was checked and was in good shape.

Mechanic noticed a riser that was too hot. New riser ordered. Old riser pulled and it seems I had used too much Permatex black Ultra a few years ago. I knew to use very little. Anyway new gasket and all is set with it. New riser not needed.
 
on both my boats, i added a $ 12 ebay " square " pump before the mechanical pump.... my boats sit 6 months to a year sometimes... 15 seconds of the little primer pump and the boat lights off like it never sat...

i however, feel the electric pump ( no matter the type/cost) is not as reliable as the mechanical pump.

i have used the priming pump for my offroad truck before, when the mechanical pump died.... best $ 12 i ever spent.
 
Originally Posted By: BrocLuno
If you are going to do the oil pressure switch, I suggest Caterpillar switches. They are rugged as a rock and very rarely fail.

Also, you'll need to add a thumb button on the dash to to make the electric pump run long enough to make sure you have a prime if the boat has been sitting a long time.

Or, you will have to manually fill the float bowl through the vent (which does not work on most marine carbs, they face down) so the engine will run long enough to get oil pressure which will then keep the fuel pump running as long as the engine runs...



BrocLuno beat me to it....
 
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