Switch for Electric Fuel Pump

[Hanover Mopar]

I am installing Painless switch panel and the electric fuel pump switch has a "Prime" and "On" position.

Does anyone prime their pump before starting the and if so for how long and does it help starting a big block.

Thanks in advance
Jack

 

[Grabinov911]

I leave mine in the On position and it comes on when the ignition is turned on. I pause to make sure I hear it before cranking the engine. If you're running a carb - with a float bowl - it will have plenty of fuel to start the car. No need to prime I would think. I don't know if EFI cars "store" fuel at the throttle body the way carbs do. I suspect not, so may be more of a requirement to prime an EFI car if it has been sitting. Even so, with modern pumps, you can push gas from the tank to the engine compartment in just a few seconds...

 

[slepr1]

My EFI conversion requires me to prime.

 

[5.7 hemi]

The "prime" on an efi set up is like pumping a carb before you start cranking the engine. It just gives the injectors a "shot" of fuel so the engine will fire, when you start cranking, the fuel pump kicks in and is running full boogie.

 

[slepr1]

Actually I need to explain my conversion. I have a Edelbrock E-Street EFI system with the remote fuel tank. You are required to prime the system, mainly on cold starts, but I find I need to do it even on warm starts.

 

[5.7 hemi]

When the fuel pump turns on, it is priming the system. Wait a few seconds, then crank the engine, it will then fire.

Am I not understanding your question correctly?

 

[Hanover Mopar]

Carb car. Starts pretty good with just an off on toggle. Just wondered if priming was a better way of starting it.

 

[383man]

On factory Mopars what happens is when the car is shut off the fuel pressure will stay up to a point as the fuel pump has check valves to hold pressure when the eng is off. On the stock Hemi's and 5.9's and so on when they sit overnight they will drop some fuel pressure. If they run at say 58 psi when you shut it off it wil drop a little to about 52 psi at first. When it sits all night it's normal to drop some more like to about 20 psi. If you have a leaky fuel injector or a bad pressure regulator on a return system or a bad fuel pump the pressure may drop to almost zero as soon as the car is shut off. But when you get in the car in the morning and it should have about 20 or more psi and as soon as you turn the key on the pump runs a few seconds and the pressure will shoot right up to 58 psi on a good system and the car will fire instantly. Basically most fuel injection systems should work about like that. Some may drop even less but as long as it has some pressure in the system it will shoot right up as soon as the pump runs any. Most EFI systems will drop a little fuel pressure overnight but they should not drop to zero or drop off as soon as it is shut off. Ron

 

[HEMI-ITIS]

With a carb setup,you should have enough fuel in the bowls,,pump & a squirt ,then fire in the hole!

 

[Yatzee]

I've never been a big fan of any switch controlling the fuel pump except the ignition switch. Even then it should be run through a relay with the ground side of the relay made through an oil pressure switch. You can see the advantage here in the event of an accident like a roll-over. There are issues with this type of system as well because priming becomes an issue when there is no oil pressure. There are companies that make a specific controller (and some are built right into newer TBI systems) that do all the work for you including a 3 sec prime. At pressures of 35psi and above it doesn't take long to move a great volume of fuel. Even in a return style fuel system with a pressure reducing regulator there is still a high pressure in the supply line even though there's only 8psi going to the carb. Even though the engine may stop in an accident, the ignition is still on, as is the pump, so a special duel acting oil pressure switch is required. I have never found an "all in one" method for priming, running and safety but I'm toying with incorporating an inertia switch and an oil pressure sensor. I've heard of "going down in flames" but I really don't want to experience it, at least not before my authorized cremation. I will opt for a proper controller when I find one but for now it's option number one with a roll-over valve in the fuel supply line.