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A fuel tank basically provides power to the vehicle. It does so by delivering the fuel to the fuel pump to the engine. Older vehicles usually have mechanical fuel pumps with carbureted engines. However, it usually operates by driving one of the major car engine parts. These are camshaft and crankshaft.  However, the electric fuel pumps for cars have fuel injected engines that drive the fuel from the fuel lines into the injectors. They are efficient at maintaining speed and performance. In this piece, we are going to discuss a very important aspect which is how to diagnose a faulty fuel pump. 

So, do you think you have a faulty fuel pump? If yes, you may need to perform the diagnosis test. Diagnosing a bad fuel pump is sometimes straightforward, but it can also be frustrating and complex.  

You should have some tricky methods to ensure that you have correctly identified the problem. Remember, there are a lot of issues that can imitate a faulty fuel pump. Check out the previous article on the common symptoms of faulty fuel pumps. It can give you valuable insights about when to replace it. Furthermore, this article will explain how to diagnose a faulty fuel pump.

How To Indicate A Bad Fuel Pump?

Firstly, you should indicate whether the problem is related to the fuel system or not. Certain conditions apply.

If The Engine Won’tWon’t Start

If the car engine does not start, it may indicate a fuel pump issue. These are the steps you need to perform.

Listen To The Fuel Pump

You need to listen and put your ear near the fuel pump by turning the ignition ” on.” If the fuel pump is working correctly, then an audible sound comes out of it. However, if it’s not, then it may create a humming or buzzing sound. 

Hit The Fuel Pump 

You need to hit the fuel pump with a sharp blow.. Additionally, whacking the fuel pump temporarily jars the internal components or the electric motor. Furthermore, this sometimes restores the fuel pump’s function, but it is a temporary fix. Furthermore, this indicates that the fuel pump needs to be replaced.

Use Starter Fluid (With Caution)

Pour the starter fluid into the throttle body of the engine while an assistant cranks the engine.  This can damage the car engine and cause personal injury. However, they should use proper equipment, such as safety glasses and a fire extinguisher. Don’t use starter fluid on a diesel engine. If the engine starts momentarily, then the problem lies in the fuel pump. Now, check the fuel pressure as the next step.

Check For Diagnostic Trouble Codes (DTCs)

You have to use a scanner or code reader to check for DTCs. Car owners set DTCs on the car’s computer. DTCs are related to the air-fuel ratio. The online auto parts store offers tools like code reading and affordable tools and apps for mobile phones. 

Check Fuel Trim With A Scan Tool 

The car owners should check the fuel trim with a scan tool. It includes both short-term fuel trim and long-term fuel trim.  The optimal fuel trim readings should be between 10 and -10. The ECM (engine module system) actually makes immediate adjustments to the fuel injection system.  Below -10 represents the low fuel trim percentage. The lean condition actually means when there is too much air inside the and not sufficient fuel in the combustion chamber. The symptoms of a bad low fuel trim include

  • Fuel injectors are leaking.
  • Low fuel pressure due to contaminated fuel filters
  • Oxygen sensors not working properly.
  • Bad coolant temperature sensor

However, the high fuel trim percentage is above 10%. It means the ECM is adding more fuel than usual for the engine to operate properly. High trim lean condition is where there is too much fuel and not enough air in the combustion chamber.  The causes of lean condition in high fuel trim are as follows.

  • Vacuum leaks 
  • Dirty Mass Airflow Sensor
  • Dirty Fuel filter
  • Exhaust leaks
  • Bad oxygen sensors

Check Fuel Pressure Or Volume

Car owners should check the fuel pressure or volume to ensure that fuel is reaching the tank. However, this does not always mean that the fuel pump is bad. There can be other reasons for this dirty fuel filter or a faulty safety regulator. They should check the owner’s manual before connecting a fuel pressure gauge.

Connect a mechanical fuel pressure gauge to the test port on the fuel rail, which mo ern vehicles have. Afterward, change the ignition to on, which means the engine is off. Note the reading and if differentiates from the specification then it may indicate a faulty fuel pump. 

Static Fuel Pressure Test

Car owners should perform static fuel pressure tests to check for adequate fuel pressure.  It helps to recognize issues like faulty fuel pumps.

Check Fuel Volume

The fuel volume testing is done when they connect the gauge and interlink the bleed end of the hose into a clean container. Afterward, start the pump for 15 seconds and hold down the valve on the tool.

Before Concluding The Pump Is Bad: Do This

Before concluding the fuel pump is not functioning, perform these steps.

Fuel Pump Electrical Circuit

The engine control module controls the fuel pump via a relay. Continuous-style fuel systems use this method, which is usually found in older vehicles. However, the fuel pump control system controls the fuel by using the fuel pump sensor to regulate its ground speed. It is one of the reliable methods to diagnose a faulty fuel pump. The control system should be checked properly before recognizing any error in the fuel pump. Use a digital multimeter for checking the wiring for continuity and power.

Fuel Pressure Regulator

Check the regulator by disconnecting the hoses and noting whether the pressure increases or decreases. If the pressure remains normal, then there is a problem with the regulator. Returnless fuel systems do not have external pressure regulators.

Fuel Filter

Continuous fuel systems have external fuel filters that are easy to replace. However, it’s easier to replace filters than to test them.

Final Note

In short, there are various methods to diagnose a faulty fuel pump. Car owners should perform these tests in order to test whether or not it’s a fuel-related issue. In addition, they can perform a whack test, use starter fuel, fuel pressure gauge, monitor fuel trim, and replace fuel filters. Moreover, they should consider buying a car fuel pump from PakWheels, a trusty online source established in 2003. Their prices range between PKR 299 to PKR 70,000. They ensure doorstep delivery with a reliable return and refund policy as well.