In last week’s article, we discussed why low fuel in the tank can lead to premature failure of the fuel pump. In this article, we will look at a few other possible causes.

In modern vehicles, an electric fuel pump is used, which is located in the fuel tank. Due to the complexity of the pump and the difficulty of access, replacement can be very expensive. With a small amount of care, the failure of the fuel pump is often preventable!

How it works

Early fuel pumps were replaceable, separately from the level sensor and pickup tube. More modern designs employ a fuel pump module. The fuel pump module consists of a fuel pump, internal wiring, anti-drain-back valve and a strainer. A sender unit sends a signal to the fuel level gauge to show the fuel level in the tank. They may also include a fuel filter, as part of the module. These fuel pump modules are most often available only as an assembly. A few have fuel senders and fuel filters that are separately replaceable.

The pump is the heart of the fuel pump module and does the work of moving fuel from the tank to the injection system. A small permanent magnet motor drives an integral pump. Fuel enters the pump through the strainer, flows through the motor and exits under pressure. Fuel pressure is critical, and the pump maintains it within a narrow range.

Older systems used a fuel pressure regulator in the front of the vehicle. The fuel pressure regulator returned excess pressure from the engine fuel rail to the fuel tank. This offered an advantage of allowing fuel to cool. More modern systems regulate pressure by varying pump voltage or with an internal pressure relief valve. Pumps with relief valves simply dump excess pressure back to the fuel tank.

Common Causes of Failure

The fuel pump is responsible for delivering fuel from the fuel tank to the engine. A seemingly simple task that can easily be compromised when outside issues affect the performance of the pump. The four most common causes of fuel pump failure are:

1. Fuel Starvation

To cool and lubricate the internal components, fuel must flow continuously through the fuel pump. Insufficient flow limits cooling and lubrication of the pump. A leading cause of fuel pump failure is running the fuel tank low. This is particularly critical on late model vehicles without a fuel pressure return system.

Running such a vehicle out of fuel once can permanently damage the fuel pump. When the fuel level is low, the pump has to work much harder to produce the same pressure. This is because the reduced fuel weight no longer pushes fuel into the pump. Instead, the pump must draw the fuel in. A low fuel level also means less fuel to dissipate heat and lubricate the pump. The combination of an overworked pump reduced cooling and lubrication will likely damage the fuel pump.

2. Fuel Contamination  

Fuel is jeopardised from corrosion, debris and moisture, which can all bring visible contaminants into the tank. Sometimes the tank itself is rusty and deposits rust particles. Irrespective, contaminants in the fuel tank are drawn through the fuel pump. The strainer on the pump will try to remove larger (more than 70 microns) particles. Unfortunately, many smaller (30-40 microns) particles pass right through and do most of the damage. Debris that enters the pump wears the commutator and brushes on the motor.

3. Electrical Issues

Often result as a direct consequence of the fuel contamination described above, As the brushes and commutator wears, the motor pulls more amperage to produce the same pressure. Additional amperage, from a worn pump, often burns the connectors inside the fuel pump. Burned connectors and harnesses on failed pumps are extremely common. Always check connections carefully, before replacing the fuel pump. Failure to replace a burned connector will cause the replacement pump to fail very quickly.

4. Insufficient Filtration 

As mentioned above, the filter keeps relatively large sediment and suspended particles from entering the fuel line. It is the first line of defence against contaminants. A clogged filter reduces the flow of fuel, and causes many of the symptoms such as backfiring, stalling or hesitation described below. More importantly, it can lead to the demise of the fuel pump in the same way as fuel starvation. Most late-model vehicles no longer have separately replaceable fuel filters. Instead, the fuel filter is part of the fuel pump and not separately available. This is unfortunate as fuel quality is a real problem and a clogged filter may mean a new fuel pump. More than ever, purchasing only high-quality fuel is important.

Summary

As the fuel pump is the component responsible for supplying the engine with the fuel required for it to run, any issues with it can cause major drivability and performance problems. Many fuel pumps issues can by being conscientious about the simple things – always having at least a ¼ tank of fuel and replacing the fuel filter regularly, if your car’s filter is not mounted in-tank.

Should you need to replace your fuel pump, Start My Car has an extensive range of fuel pumps and modules. Have a look on our website