Mechanical Fuel Pump return port.

[TheSilverBuick]

This hopefully is a simple question.

I've installed a hi-volume Buick 455 mechanical pump on the Skylark, and it has a return line port on it, which I just plugged off.

How do the return on the mechanical pumps work? Is there a relief valve in the pump so when it hits ~5-9psi it pumps the excess volume out the return port? Will plugging it off become a problem down the road? The main pressure line is not dead headed and there is no significant restriction to it's flow (flows into my surge tank/pipe which has an open line to the gas tank). If it's a problem, then I'll figure out a way to T it into the surge tank.

[SuperBuickGuy]

Re: Mechanical Fuel Pump return port.

I don't know the mechanics of it - but on my 500 caddy, the return has been plugged since I pulled the motor (damn) 12 years ago (long time)... it works just fine.

[STINEY]

Re: Mechanical Fuel Pump return port.

Its there to help with vapor-lock, especially on air conditioned cars. Rudimentary way to keep fuel cooler. It will cause no problems blocked off, yet may possibly help if there were a vapor lock problem.

Which is not likely in your situation now is it? Doesn't EFI negate vapor-lock? ;)

[TheSilverBuick]

Re: Mechanical Fuel Pump return port.

I actually still have a minor concern about vapor lock now that I removed the pusher pump at the tank and replaced it with a puller pump at the engine (though lower than the gas tank) because I have one spot where the fuel line goes over the frame to behind the cross member that gets close to the header. With a pressurized line I didn't worry too much about it, I'm slightly concerned with the current arraignment. So for the time being I've left a splice in the hose at the tank with the wiring in place so I can fairly quickly re-install the electric pump if I run into a vapor lock situation. However it will have a constantly flowing fuel in the line since it's not dead headed.

I had a bad vapor lock issue with this engine and the Q-jet, and the kick in the rear to make the EFI swap was from boiling the carb so bad it didn't run right afterwards.