Engine Fuel System – Proper Testing Procedures With Solutions

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

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.

Choosing a fuel that can perform injector cleaning, 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. Consequently, a failure in any of these engine components, can have a devastating effect, on performance and reliability.

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 Electric 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 engine fuel system may require, 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. And, 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 (engine fuel system)

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:

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

Running Fuel Pressure Test (engine fuel system)

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 (engine fuel system)

Fuel Volume Test Kit
Fuel Volume Test Kit

So, it 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 fuel pressure regulator. As a rule, the engine 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.


So, checking fuel pressure is an essential part, of fuel injection system troubleshooting. But, before doing any testing, it is a good idea to understand how, engine 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.
  • Next, the fuel in the pressure line, feeds the fuel injectors.
  • In the end, the fuel in the return line, returns to the fuel tank.

It’s not rocket science, but a good understanding of how the engine fuel system works, can save you money.

Thank You !