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ABS Speed Sensor
Air Flow Meter / Sensor
Air Intake Pressure Sensor
Alternator Current and Voltage
Amplifier Earth
Camshaft Sensor
Carbon Canister Solenoid Valve
Crankshaft sensor
Coolant Temperature sensor
Diesel Glow Plugs
Digital ECM to Ignition Amplifier Signal
Distributor Pickup
Dual Trace
Electronic Fuel Pump
Exhaust Gas Recirculation
Idle Speed Control Valve
Knock Sensor
Lambda Sensor
MAP Sensor
Relative Compression
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Electronic Fuel Pump Current Diagnostics

This test 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. The 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.

Technical Information

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 system.

The normal 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!

A cross section of an electric fuel pump.

A submerged fuel pump located within the fuel tank.

The majority 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 rear seat.

Mounted 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.

A typical wiring diagram for a modern system whereby the Electronic Control Module (ECM) controls the earth path of the fuel pump relay.