Holley COMMANDER 950 - Manual (Page 10)

10
1.13 Electric In-line Fuel Pump
The function of the electric fuel pump is to deliver pressurized fuel to the fuel injection system. The ECU activates the fuel
pump relay to operate the fuel pump when the ignition switch is in the On or start position. The pumps are designed to match
certain flow and pressure specification for the engine application. In TBI applications, the fuel pump must supply enough fuel
flow for the engine Wide-Open Throttle (WOT) output at 15 to 20 psi. In multi-port applications, the fuel pump must be able to
supply enough fuel at full engine load to maintain at least 43.5 psi at the fuel rail. At idle, the fuel pressure regulator must be
able to return the excess fuel to the tank and maintain the required system pressure. Most of the cars prior to 1987 use an
in-line external electric fuel pump.
In-line Fuel Pump High-Flow In-line Fuel Pump High Performance Race Pump
1.14 Electric In-tank Fuel Pump
Almost all car applications after 1987 designed their fuel pump assembly inside the fuel tank. The advantage of having the fuel
pump in the fuel tank is mainly lower noise, lower potential leakage problems, and less mounting sensitivity of the pump with
respect to lift of fuel from the tank. The in-tank pump went through several designs evolving from a simple "pump on a stick"
to a complex in-tank, fuel-sending module. The new designs combine the high-pressure electric fuel pump, noise isolation,
and a fuel level sensor into one compact modular package. This new design also helps in reducing hydrocarbon emissions.
The hot gasoline returning from the fuel system is returned to the reservoir surrounding the fuel pump. By returning the hot
fuel to the reservoir heating of the bulk fuel in the fuel tank is avoided, thus reducing the evaporation of the high volatile
portions in the fuel. At present, all fuel tank modules are designed and serviced as a complete unit. If the pump or fuel level
sensor fails, the entire unit will have to be changed.
NOTE: Never use an in-tank, low-pressure fuel pump in conjunction with an external high-pressure fuel pump. The low-
pressure, in-tank fuel pump will become a restriction to the external, high-pressure fuel pump. This condition will
result in fuel starvation and engine damage.
Aftermarket In-tank Pump Stock-style pump module
1.15 Fuel Pump Inlet Filter
The function of this filter is to eliminate any impurities that might harm the fuel pump. In the
in-line fuel pump type, this filter is external to the fuel tank and is in a replaceable cartridge
filter. In the in-tank fuel pumps, the fuel filter is in the form of a sock and is directly attached to
the pump in the "pump on a stick" version and attached to the fuel pump module in the module
version. These filters have a rating of 120-150 microns.
Fuel Pump Inlet Filter
NOTE: This fuel filter is required to avoid fuel pump damage.