The fuel pump is an important part of a gasoline engine. It pumps the petrol from the tank and delivers it to the engine to make the motor run. A vehicle can drive a few kilometres with a faulty fuel pump, but once the petrol in the lines are exhausted, the engine will stall.
There are a few tell-tale signs and symptoms that the fuel pump is malfunctioning before it will die completely. Keeping an eye out for these signs can prevent further damage.
The Car Won't Start
The most obvious symptoms is if the car won't start at all or starts poorly. This means the engine is not getting enough fuel to turn over. First, make sure there is gas in the tank. Many people immediately think there is a problem with the fuel pump only to discover the tank has run dry. This can easily happen with a faulty gas gauge.
Sputtering and Stammering
When the engine isn't getting the amount of fuel it needs, it will stutter and stammer. This can occur when trying to start or while driving. Again, the problem could be not enough fuel in the tank, but most likely the pump is not working properly.
There are many other reasons why a car may stutter or stall. A simple test will determine if the problem is with the fuel pump. Put the key in the ignition and turn it to the auxiliary position. Do not turn it all the way over. If the pump is working, there will be a humming sound. If you don't hear this sound, the pump may need to be replaced.
Diagnosing the Problem
A low-reading analogue ammeter or a digital multi-meter with a high enough current carrying capacity is needed to test the amperage. This can be done by either connecting the meter in series with load, or with an inductive pick-up clamped around the wire. The second method works best with large current flow like the one in the starter circuit. For fuel pump testing, the first method is preferred. However, this method requires breaking into the circuit. Take one of the ammeter leads and connect it to the positive voltage post on the battery. Connect the other lead to the hot wire on the pump. The precise reading will be in the service manual, but as a general rule, anything over five amps with a low pressure version or seven amps with a high pressure system means trouble.
Check the Fuel Filter
The fuel filter should be replaced at regular intervals. If this hasn't been done, that could be the cause of the problem. Before removing the filter, release the pressure from the system. Wear protective gloves or wrap a heavy cloth around the Schrader valve on the fuel rail while pressing down on the valve pin. Alternatively, the fuel pump fuse can be removed and the engine cranked for 20 seconds. Next, check the fuel pressure with a pressure gauge. Gauges commonly screw onto the Schrader, but on some cars a special banjo connector is needed.
Turn on the engine and read the gauge. A reading of no or very low pressure could mean the electrical circuit in the pump is faulty, which might mean the control relay has worn out. Before replacing the relay, check the connections. The problem could be loose wires. Also check for corrosion. Badly worn or corroded wires need to be replaced. Test the voltage of the battery at the pump terminal and then make sure the wires are all well ground.
Replacing the Pump
After all of the tests are completed and the diagnosis is a faulty pump, it's time to put in a new one. Find everything you need to replace the pump online. Accessing the pump can be tricky due to the design of some cars. On others, it is simply a matter of folding back the boot mat and removing a panel. Once access is gained, the rest is straightforward. Follow the directions that came with the new pump and everything should go smoothly.