will show the current for each individual sector of the commutator. The
majority of fuel pumps will have 6 to 8 sectors and a repetitive point on the
waveform can indicate wear and an impending failure.
current drawn by the fuel pump is dependent upon the fuel pressure but should
be no more than 8 amps found on the Bosch K-Jetronic mechanical fuel injection
which has a systems pressure of 75psi.
This type of
high pressure fuel pump is denoted as a roller cell pump, with the fuel
entering the pump and being compressed by rotating cells that force it through
the pump at a high pressure. The pump is capable of producing a pressure of 8
bar (120 psi) with a delivery rating of approximately 4 to 5 litres per
minute. Within the pump is a pressure relief valve that lifts off its seat at
8 bar to arrest the pressure if the filter or fuel lines or other
eventualities cause it to become obstructed. The other end of the pump
(output) is home to a non-return valve, that when the voltage to the pump is
removed, closes the return to the tank and maintains pressure within the
operating pressure within this system is approximately 2 bar (30 psi) and at
this pressure the current draw on the pump is 3 to 5 amps. Fuel passing across
the fuel pump's armature will be subjected to sparks and arcing, this on the
surface appear quite dangerous, but the absence of oxygen means that there
will not be an explosion!
section of an electric fuel pump.
submerged fuel pump located within the fuel tank.
of fuel pumps fitted to today's motor vehicles are fitted within the vehicle's
petrol tank and are referred to as submerged fuel pumps. The pump will
invariable be located with the fuel sender unit and both units can sometimes
be accessed through an inspection hole either in the boot floor or under the
vertically, the pump comprises of an inner and an outer gear assembly which is
termed as the 'geroter'. The combined assembly is secured in the tank using a
series of screws and sealed with a rubber gasket, or with a bayonet type
locking ring. On some models Volvo fit two fuel pumps, the submerged pump
acting as a 'lift' pump to the external roller cell pump.
typical wiring diagram for a modern system whereby the Electronic Control
Module (ECM) controls the earth path of the fuel pump relay.