The fuel pump reliably supplies the car’s combustion engine with fuel. If the fuel pump is defective, clear symptoms quickly appear. In our guide, you can find out which signs indicate that the pump is defective and what the possible causes are. In addition, everything you need to know about replacing the fuel pump and the necessary spare parts.

Function of the fuel pump in the vehicle

A fuel pump ensures the steady delivery of fuel from the car’s fuel tank to the engine. Modern vehicles with fuel injection systems often have another high-pressure pump that provides the necessary pressure for injection. In this case, the fuel pump only has the function of a pre-feed pump between the tank and the engine compartment.

The position of the fuel pump or diesel pump in the vehicle may differ depending on the model. Today, modern cars use pumps as in-tank fuel pumps. These pumps in the form of a fuel delivery unit are installed directly in the tank. A pump inside the fuel line from the tank to the engine is called an in-line pump.

Common causes of fuel pump defects

If fuel pumps such as the petrol pump or the pump for diesel are defective, there are various possible causes. The fuel pump of modern vehicles is designed for a long service life. However, with higher mileage, wear and tear occurs on the pump, which can lead to the fuel pump breaking down. With modern fuel pumps, the electric motor sometimes fails or seizes up. A mechanical pump can break down due to broken parts in the mechanics.

Causes of defective fuel pumps at a glance:

• Wear of the pump with higher mileage
• Damage to the pump unit due to bad fuel
• Fuel pump seals are porous
• Damage to mechanical parts inside the pump
• Power supply to the fuel pump is interrupted

Poor fuel or leaks

Dirty or low-quality fuel is also a possible cause of a defective fuel pump. Dirt particles can easily damage the components inside the fuel pump. The seals of the pump or a diaphragm inside also become porous over time. Leaks then occur in the area of the fuel pump. In some cases, it is not the pump itself that is broken, but fails due to a defective power supply.

Typical symptoms of a fuel pump defect

If the fuel pump is defective, typical symptoms often indicate this. With a defective fuel pump, the engine is no longer sufficiently supplied with fuel from the tank. The pressure in the fuel system is reduced or the required amount of fuel is not available. In this case, the combustion engine can no longer function optimally.

Rough engine running and loss of power

One of the typical signs of a defective fuel pump is that the engine does not run smoothly. Due to the malfunction of the fuel pump, petrol engines are prone to misfiring or faulty ignition. The affected engines sometimes sound unusual and run poorly. In all engine types, a defective fuel pump also leads to a loss of power.

Unusual noises from the engine compartment or misfiring can also indicate a broken fuel pump. In addition, a broken fuel pump or diesel pump is often noticeable by a jerking of the vehicle. Modern vehicles report a malfunction of the pump by a corresponding error message in the instrument cluster.

Symptoms of a defective fuel pump at a glance:

• Engine starts badly or not at all
• Engine power is significantly reduced
• Vehicle accelerates jerkily
• Engine tends to misfire
• Error message for the fuel pump

Poor engine start or fuel leakage

A fuel pump does not always fail completely from one moment to the next. Often, problems with the fuel supply, such as poor starting ability, become apparent beforehand. In some cases, leaks also occur when the fuel pump is defective. If this causes fuel such as petrol or diesel to flow out, quick action is required. For this reason, repairs to the fuel supply should never be postponed.

Changing the defective fuel pump in the car

A defective fuel pump should be replaced promptly. This is the only way to ensure proper functioning of the combustion engine. If a pre-feed pump is defective, the high-pressure pump may be damaged as a result. This causes further costs in the workshop. If fuel even leaks out of the pump, safe and environmentally friendly operation of the vehicle is no longer possible.

Replacing a fuel pump in 5 steps

Changing an in-tank fuel pump is often done quickly. However, the operation should only be carried out by expert car mechanics or by a professional workshop. Petrol or petrol vapours leaking during the repair can easily become a hazard.

1. Diagnosis of the defect: The failure of the component can also result from causes such as a defective power supply. Therefore, a comprehensive search for the fault is recommended.
2. Removing the rear seat: Depending on the model, the pre-feed pump is installed in the tank under the rear seat. Therefore, it must be dismantled before the component can be replaced.
3. Remove the fuel pump: Once access has been gained, the defective part is removed. To do this, remove all connections and take the pump unit out of the tank.
4. Compare spare part: Before installing a new pump, it should be compared with the existing one. Often information such as the part number can be found on a sticker.
5. Install the fuel pump: The installation of the fuel pump as a spare part is done in reverse order. After installation, a test is carried out and the rear bench is refitted.

Fuel pump defective – repair or change

Repairing a defective petrol pump is usually not worthwhile. Pumps for petrol or diesel are relatively difficult to disassemble and repair. Many fuel pumps have reached the end of their service life and are completely worn out when they finally break down. Thanks to good offers, however, fuel pumps for many models can be bought cheaply second-hand.

Cost of replacing the fuel pump

The costs for changing a fuel pump or diesel pump in the workshop vary depending on the vehicle. Depending on the manufacturer and the position of the fuel pump, the replacement can be more or less time-consuming. As a rule, the workshop needs at least one hour to change the fuel pump. The cost of the replacement is made up of labour time and the cost of the component. It is worth comparing offers here.

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