2 fuel pumps...............?

[mrnda]

1984 C20, 350, auto trans, edelbrock 1400 carb.

Had an intermittent  fuel feed problem, pulled the fuel line to the carb... no fuel when cranking.
Followed the fuel line to the tank and found an electric fuel pump after the tank selector valve (dual tanks) but before the mechanical pump, the electric pump was not pumping.
Followed and removed the hot line for the pump, it had a short causing the intermittent problem.  Ran a new line and the pump runs like it should.

Issues---how common is a truck with 2 fuel pumps? after running the new line the truck would not start.  I pulled the fuel line off the carb to see if fuel was flowing with just the electric pump. 
There was healthy fuel flow with just the electric pump. IS THE FUEL SUPPOSE TO BE ABLE TO FLOW PAST THE MECHANICAL PUMP?
I have not put a gauge on it so i do not know pressures.

Thanks.

[bd]

1984 C20, 350, auto trans, edelbrock 1400 carb.

Issues---how common is a truck with 2 fuel pumps?  ...IS THE FUEL SUPPOSE TO BE ABLE TO FLOW PAST THE MECHANICAL PUMP?

I think the electric pump was probably added later, perhaps to solve some real (or imaginary) problem - for examples: vapor locking, fuel starvation, or 'high performance.'  The design of the check valves in the mechanical pump will allow fuel from the electric pump to flow through with little interference.

[bake74]

      Sounds to me that the electric fuel pump may have been added when the mechanical pump was having problems, as bd said, the mech. pump will allow fuel through. 

[mrnda]

Gentlemen,  Thank You very much for thi info i can go forward with the issue and start looking at the carb and ignition for the no start.

Appreciate it greatly.

[Captkaos]

No GM 73-87 truck ever had an external electric fuel pump on it.  Just wasn't necessary.