Engine Fuel System Testing – Proper Testing With Solutions

Engine Fuel System Testing - Proper Testing With Solutions
Engine Fuel System Testing - Proper Testing With Solutions

So, the engine fuel systems job sounds pretty basic. It delivers fuel from the fuel tank to the engine.

Testing the engine fuel system is relatively simple. The engine fuel system consists of the filler hose, fuel tank, fuel pump, fuel filter, fuel injection and fuel lines.

So, the engine fuel system needs to do two important things. It needs to get the fuel to the engine and it needs to have the correct pressure and volume.

Consequently, a failure in any of these engine fuel system components can have a; devastating effect on performance and reliability. So, the engine fuel system doesn’t need a lot from you. But, what it does need is periodic filter replacements and fuel injector services. Opting for a fuel that can perform injector cleaning, such as box diesel, could also be an option to consider. Furthermore, the engine fuel system is critical in storing and delivering the fuel your engine needs to run.

There are several indications that can alert you to a problem in your engine fuel system such as:

  • Electrical clicking noise
  • Hard starting
  • Lack of responsiveness
  • Sudden decrease in power

So, if you think you are experiencing any of these symptoms, you need to check these things first:

  • Check for fuel in the tank
  • Listen for fuel pump noise
  • Make sure the timing belt is okay
  • Check for a plugged fuel filter
  • Check the vacuum line to the fuel pressure regulator
  • Make sure there is fuel in the fuel lines

The First Thing To Test Is The Fuel Pump

Electric Fuel Pump Access Panel
Electric Fuel Pump Access Panel

Does the pump run when the engine is cranking? The fuel pump should make a buzzing noise. No noise would tell you the pump is not working.

The pump circuit may be wired through an oil pressure switch and/or an inertia safety switch. Consequently, killing the pump in case of an accident. Always refer to the wiring diagram to find out what is involved before jumping to any conclusions.

Fuel Pressure Testing

So, depending on the application, the fuel system may require anywhere from 30 to 80 psi of fuel pressure. Also, pressure specifications will vary according to the type of fuel injection system on the engine. There are no rules of thumb. Every application is different, so always look up the pressure specs when troubleshooting fuel-related performance problems.

High Fuel Pressure

Fuel Fouled Spark Plug
Fuel Fouled Spark Plug

When there is too much fuel pressure, the engine runs rich.

As a result, this causes an increase in fuel consumption and carbon monoxide (CO) emissions. An engine that is running really rich also may experience a rough idle, surging and possibly even carbon-fouled spark plugs.

Low Fuel Pressure

So, when there is not enough fuel pressure, the engine may not start. Or if it does, it may idle rough and run poorly.

Low fuel pressure creates a lean fuel condition that can cause:

  • Lean misfire
  • Hesitation
  • Rough idle

There Are A Number Of Different Fuel Pressure Tests You Can Do:

Static Fuel Pressure Test

Checking Engine With Low Fuel Pressure
Checking Engine With Low Fuel Pressure

So, this test measures the sustained fuel pressure recommended by the manufacturer. It can be performed by simply energizing the fuel pump. When the fuel pump is energized it will raise the fuel pressure and hold it steadily at a fixed value.

If the pressure reading is lower than normal the cause can be:

  • Blockage in the fuel line
  • A weak fuel pump
  • Blocked tank or filter inlet
  • Faulty pressure regulator

Residual Fuel Pressure Test

So, when the pump is turned off, the system should hold residual pressure for several minutes.

If pressure drops quickly, the vehicle may have:

  • A leaking fuel line
  • A leaking fuel pump check valve
  • Leaking fuel pressure regulator
  • One or more leaking fuel injectors

Low residual fuel pressure can cause hard starting and a vapour lock during hot weather.

Running Fuel Pressure Test

So, this test is performed by idling the engine and comparing the gauge reading to the specifications.

If the pressure is low it indicates:

  • A worn out fuel pump
  • A clogged fuel filter
  • Bad fuel pressure regulator
  • No fuel in the tank

Dead Head Pressure Test

So, this test checks the maximum output pressure of the fuel pump. If you pinch the return line, the pump should produce double the normal operating pressure at idle. Consequently, if the pressure fails to rise, it may not be able to deliver sufficient fuel at high engine speeds.

The causes of this failure may include:

  • Low voltage to the fuel pump
  • A worn out fuel pump
  • An obstructed fuel line

Fuel Volume Test

Fuel Volume Test Kit
Fuel Volume Test Kit

So, a fuel volume tests the pump’s ability to deliver; the correct volume of fuel over a certain period of time. You could have correct fuel pressure and still have driveability issues. Due to, the fuel pump not being able to deliver enough fuel volume to meet the engine’s needs.

The main causes of low delivery of fuel volume include:

  • Plugged fuel filter
  • A worn out fuel pump
  • No fuel in the tank

Fuel Pressure Regulator Test

Fuel Pressure Regulator Located On Engine
Fuel Pressure Regulator Located On Engine

So, this test checks the regulator to ensure that it changes line pressure with respect to changes in engine vacuum. With the engine running, disconnect the vacuum hose from the pressure regulator. As a rule, the fuel system pressure should increase 8 to 10 psi with the line disconnected. No change would indicate a faulty pressure regulator, or a leaky or plugged vacuum line.


Consequently, checking fuel pressure is an essential part of fuel injection system troubleshooting. Before doing any fuel pressure testing, it is a good idea to understand how fuel system components work:

  • So, the fuel pump pumps fuel from the fuel tank to the fuel pressure regulator.
  • Then, the fuel pressure regulator divides the fuel between the pressure line and the return line.
  • Furthermore, the fuel in the pressure line feeds the fuel injectors.
  • In the end, the fuel in the return line returns to the fuel tank.

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