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Latest News Testing Electric Fuel Pumps What Technicians need to know when testing fuel pumps and related circuits when suspecting a fuel system fault. There are of course many electrical circuit or fuel pump causes of “low or nil” fuel pressure or flow. Understanding the simple electrical control and load circuit types will assist the technician in quickly and accurately pinpointing the test procedure required for that specific circuit. Typical PCM positive relay control. (Power side switched) e.g. VE Commodore – Pre SIDI
On this system, the PCM will activate the relay with a power supply to the relay control circuit. Testing this Circuit:
Testing Load Circuit:
Note: there are areas where interruption to the circuit may be created and the circuit integrity must be validated. Typically: Hitting a large pothole or being involved in a vehicle accident may trigger the Inertia switch which Isolates the fuel pump from the relay if fitted. (for safety reasons)
This inertia switch is generally able to be simply reset. Incorrectly fitting this unit or a loosely mounted unit may intermittently trigger and interrupt the load circuit.
Typical PCM ground relay control (Ground side switched) e.g. – Ford FG Falcon with inertia switch.
On this system, the PCM will activate the relay by grounding the control circuit. The power supply to the control circuit, generally originates from a suitable relay. Testing this Control Circuit.
Testing Load Circuit:
Note: the test procedure for this load circuit is similar to the previous system. Testing Fuel Pump Integrity with an Oscilloscope and Amp meter. It is important to identify if the vehicle being tested has a standard constant voltage fuel pump circuit or is fitted with a fuel pump driver module prior to carrying any current flow testing. A fuel pump driver module with pulsed width modulated output will of course vary the indicated circuit current flow as the pulsed output varies. These fuel test expectations will vary compared to the standard fuel pump constant power supply system. Why test the pump circuit current flow? Carrying out a fuel pressure test on a vehicle will indicate if the fuel pump can supply the fuel pressure required for basic system operation during the test, but not the condition of the fuel pump. A fuel pump that is problematic may still supply the required fuel pressure but may be operating with a higher current draw due to internal issues that could indicate possible reduced fuel flow and possible future fuel pump failure. Any armature and/or commutator issues may also be visible on the oscilloscope.
Note: Be aware that fuel pressure is directly related to current flow and fuel flow. That is – If the fuel pressure has been increased, the current flow also will increase, and the fuel flow will “decrease.” This should be taken into consideration when carrying out relevant tests.
Note the increase in current flow (as the result of fuel pressure increase) and the fuel flow decreases to levels that could potentially cause major engine damage. The Premier Auto Trade Fuel range includes almost 800 Fuel Pumps from the world’s leading manufacturers, covering over 12 million vehicle applications in Australia and NZ. When you supply and fit products from Premier Auto Trade you can expect a product designed and tested to the vehicle manufacturer’s specifications offering OE form, fit and function. Premier Auto Trade distributes products throughout Australia via a network of specialised resellers and leading automotive groups. |
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