I have decided to add an electric fuel pump at the tank. What psi range is optimal for supplying the Motorcraft carb?
What is your reason for wanting to add the electric pump? I don't think you want to mix a mechanical and electrical pump. Usually just one or the other. The Motocraft likes 4-5 psi.
I need it to create and maintain fuel pressure between the pump and tank. I thought that 4-5psi would be optimal. Once the pressure is correct, there shouldn't be any issues with using the mechanical pump.
I was planning on using this one full bore.
http://www.ebay.com/itm/AIRTEX-E8016S-ELECTRIC-FUEL-PUMP-UNIVERSAL-EXTERNAL-CARBURETOR-2-5PSI-4PSI-12V-/310491414221 (http://www.ebay.com/itm/AIRTEX-E8016S-ELECTRIC-FUEL-PUMP-UNIVERSAL-EXTERNAL-CARBURETOR-2-5PSI-4PSI-12V-/310491414221)
Sorry, I'm still a little confused. Are you having fuel delivery problems? The mechanical pump is a puller pump. They shouldn't have any problems pulling fuel from the tank and supplying ample pressure for a carburated engine. There shouldn't be any pressure between the mechanical pump and the tank. It might put undo stress on the diaphragm of the mechanical pump and possibly cause the crankcase to fill up with fuel. I have a stock replacement mechanical pump feeding my Motorcraft with an adjustable fuel pressure regulator set at 4.5 psi. My engine is worked over a bit and I have no fuel delivery problems. If you want to run an electric pump. I would bypass the mechanical pump.
eagle freak is correct. Pick one or the other. Don't put pressure on the backside of the mechanical pump. Not only is there a possibility of the diaphragm rupturing and filling the crank case with fuel or spraying fuel out the vent and all over your engine, engine compartment, and the ground, but you may just defeat the mechanical pumps spring, filling the pumping chamber with fuel keeping the diaphragm from being lifted by the pump lever. in essence bypassing the mechanical pumps ability to pump. The spring under the diaphragm is actually what is pushing the fuel to the carb. The pump levers only job is to compress that spring pulling the fuel into the chamber. then the spring pushes that fuel toward the carb as needed.
Also, the pressure on the backside may cause the check-valve in the mechanical pump to remain open or not fully seat defeating the springs ability to push the fuel to the carb, pushing fuel in 2 directions, back against the electric pump and up to the carb.
If you are having problems with the mechanical pump, look for the reason why. Is the pump bad? is the pickup in the tank plugged up? Is the fuel filter plugged up? do you have a crushed fuel line? Is the carb starving for fuel: is the float set correctly, or is the float valve sticking closed? If the mechanical pump is good and you still have problems, you could install the electric pump and still have the same problems.
If you install the electric pump, make sure it is as close to the fuel source as possible because it is designed to push fuel not pull it.
In a diesel many times you will have a lift pump and then the main pump to the injectors. But system is designed that way.
Well, right or wrong, I have decided to eliminate the mechanical pump as a source of potential problems. But that still leaves my original query unanswered.
4-5 psi is what I have heard and that's what I have my fuel pressure regulator set for.
OK. I will start with 5psi.