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Fuel pump defective: symptoms & testing

If the fuel pump is defective, the engine is no longer supplied with sufficient fuel. If the fuel or diesel pump fails, the car comes to a standstill. For this reason alone, the repair of a defective fuel pump will not tolerate any delay, because the final consequence would be to tow the car all the way to the workshop.

What is the function of the fuel pump?

In principle, the fuel in the vehicle can reach the carburetor or injection system in two different ways. In simple vehicles, this is done by gravity because here the fuel simply flows from the top of the tank down into the carburetor. In more modern vehicles, on the other hand, it is not quite so simple. Here, a fuel pump is installed, which continuously supplies the engine with fuel in sufficient quantity and with sufficient pressure.

Wear often leads to pump failure

Today, mechanical and, above all, electric fuel pumps are in common use, with the mechanical variant only being found in classic cars. Modern pumps normally provide their service for many years. A defect in the fuel pump is therefore rather rare. But a high mileage still makes the fuel pump a wearing part.

Recognizing a defective fuel pump

As is often the case, there are various signs that may indicate a defect. Below is a selection of the most common symptoms:

  1. The car does not start. Alternatively, the car may start poorly or not always on the first try.
  2. The engine run seems and sounds “unclean” and “out of round”.
  3. Your vehicle has – usually above a certain rpm – limited power.
  4. The engine stalls / dies off while driving.
  5. Your vehicle may have bad exhaust gas values.
  6. Message in the error memory such as “insufficient delivery”.

How long will fuel pump last?

Symptoms and consequences of a defective pump

Symptoms of a defective fuel pump can include a drop in engine performance, occasional engine misfires, poor starting behavior and engine judder. These signs are clearly recognizable even to the layman. As a result, the drivability of a car is reduced. Safety is then no longer guaranteed because the car can become unpredictable in road traffic. If the pump fails, the car comes to a standstill.

Possible causes of a defective fuel pump

The general causes of a defect can be contamination inside the pump or even a leak. For mechanical pumps, broken diaphragms or a broken pump lever are also possible. For electric pumps, defective power contacts or relays, broken wires, and blown fuses are the most common causes.

Have the fuel pump checked at the workshop

The professional at the shop will inspect the fuel pump according to a set schedule to isolate the fault and repair it. If the lines, seals, levers, and fuses are without defects, the only thing left to do is to change the pump.

Changing the defective fuel pump

The fuel pump can be found in different installation locations depending on the vehicle model. Mechanical pumps are attached to the engine. Electric pumps are usually somewhat “hidden” between the fuel filler cap and the rear seat, or even installed inside the tank. The workshop has some special keys or unlocking tools to facilitate removal. Depending on the type of vehicle, the pump may consist of several parts (basket, holder, strainer, screw ring, etc.). Specialists replace a defective pump with high-quality original or identical parts without exception. Installation and connection of the new pump must be done in the correct order. All in all, special tools, intuition, and experience are required for a replacement.

Can you still drive with a defective fuel pump?

If you have discovered damage to the fuel pump, you can generally continue to drive the vehicle for a while, but it may happen that the car will no longer start at some point. For this reason, if you suspect a defective fuel pump, you should visit a workshop as soon as possible or, if you are confident enough to change a pump yourself, you should do so as soon as possible.

Changing the fuel pump

Anyone who is technically proficient can easily replace a defective fuel pump themselves if the following points are observed. The change takes one to two hours.

In most cars, the fuel pump is located in the tank. In this case, changing the pump is done as follows.

  1. Remove the lower part of the rear seat.
  2. Unscrew the fuel pump cover.
  3. Disconnect the retaining ring, fuel lines, and connector.
  4. Pull out the fuel pump upwards and drain it. This is easiest if the tank is not completely full.
  5. When it has dripped, then lift it out completely.
  6. Install the new pump in reverse order.

How to change fuel pump? - Video


How to notice that the fuel pump is defective?

The car starts poorly or not at all, accelerates significantly worse and the engine bucks.

Where is the fuel pump installed?

The fuel pump is normally installed in the tank and is comparatively easy to reach and replace.

Is it possible to repair the power stop pump?

A fuel pump cannot be repaired. If it is defective, the pump must be replaced.

David Muench (Carnes Mechanical)

David Muench (Carnes Mechanical)

Hey, I’m David. I’ve worked in a cars store for 6 years. I write reviews and guides, helping people to choose the most suitable technicals and best product for them. I’m happy to finally share my knowledge of the industry here, on CarnesMechanical.

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