New Electric Fuel Pump

[gmilburn]

Hi all,

I've just made the conversion from the stock mechanical fuel pump to a new electric fuel pump from MM. My question is how does the carb get primed to fill the carb with fuel (it's a brand new carb as well) when the oil pressure switch prevents the pump from pumping? What am I missing here? You need fuel to start the engine to generate oil pressure to switch the fuel pump to work.

Help me understand!

Thanks

[sastanley]

The theory is there is enough fuel in the carb bowl to start the motor and the fuel pump will pressurize the fuel system once the engine is running well before it burns everything out of the bowl.

Also, enough cranking should generate enough oil pressure to trip the switch too..but the A-4 should start within seconds if you have it tuned correctly.

If you wanna send me your old mech. fuel pump, I'll pay shipping.

[roadnsky]

...If you wanna send me your old mech. fuel pump, I'll pay shipping.

Pump hog!

What Shawn said. Turn the engine over (water input closed) until it primes.
A virgin pump and carb should take about 10-15 sec max.

You can also "hot wire" the pump if you want to run it for a bit prior to turning over the engine.

[TomG]

Depending on tank and filter arrangement, it might take more than a few seconds if the the filter(s) and bowl are dry. My boat has the fuel tank waaaaay aft with the Racor and polishing filters just abaft the mast. I routinely "jump" the OPSS to get the fuel from the tank and through the filters. A had an issue when I first got this boat where the electric pump wouldn't bring fuel to the carb. After some counseling from Ken at MMI, I primed the filters with an outboard priming bulb. Everything worked fine from then on.

Possible bad facet Fuel Pump?

[ndutton]

Make a small jumper out of 14 gauge wire with an alligator clip on each end. Whenever you feel the need to prime the carburetor bowl as in the case of after a rebuild when it's dry, place the jumper on the OPSS tabs and give the engine a crank (assumes you have a two tab OPSS). As Shawn said, after that there's sufficient fuel in the carb bowl to start the engine next time and keep it running at idle for a minute or so. Long before then the OPSS will activate the pump, like within a second of starting.

Remember to remove the jumper after the bowl is primed.

[Marian Claire]

Just remember to do the sequence as described in Neil's post. Make the connection first then energize the system. Connecting the jumper after the system is energized can cause sparks. Dan S/V Marian Claire
Edit: My system is energized when I turn the key on. There is a separate button to engage the starter. So I can prime the fuel system without turning the engine over.

[joe_db]

I have a prime button on my engine panel. I turn on the ignition, hold the prime for about 5 seconds, and then hit the starter. The button is wired to jump across the oil pressure switch. I could have wired the switch to work with the ignition off, but I worried about someone doing a "what is this button for"
If the engine is warm and I haven't run the gas out it literally starts in about 2 seconds without any need for prime.

[Whippet]

I like the concept of a "prime switch" and has joined my long list of future projects. Can you clarify the "fuel pump switch" in your diagram. Is this one more switch on your panel activated automatically? Thanks

[joe_db]

The fuel pump switch is on my panel between the ignition and blower switches. The oil pressure switch is the automatic one.

[JOHN COOKSON]

You can co join a wire to the terminal that holds the wire from the electric fuel pump. The other end of this wire goes around to the "R" terminal on the starter solenoid. This way as the engine is being cranked the OPSS will be bypassed and the fuel pump will operate.
My late model A4 came from the factory wired this way. Also this bypass wire is shown in the wiring diagram in my original late model A4 owner's manuel.

TRUE GRIT