How to Test Fuel Pressure

How to Test Fuel Pressure

A car’s engine requires only four things for operation, such as- spark, fuel, air, and compression. Proper fuel pressure is such a thing that leads an engine to appropriate function. To understand the appropriate way of how to test the fuel system in a car (e.g. Passenger car, travel trailer), it is necessary to have few ideas about how the fuel is delivered to the engine yet.

Usually, the modern multiport fuel injection is a precise, more environmentally friendly system. This modern fuel injector electronically controls and sprays the required fuel to the engine. Though it is a bit less costly but dependable yet, on the other hand, the traditional carburetor (throttle body fuel injection) pumps the fuel into the engine. Although the carburetor is less environmentally friendly, it is more reliable and cost-effective as well.

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Basically, the fuel is pumped from the fuel tank through filters to the fuel rails from where the injectors take the fuel and spray them into the combustion chamber. Whereas, there are two types of pumps being used today. The mechanical pump that pulls the fuel from the tank and delivers it to the engine and the electronic pump pushes the fuel to the engine. 

Fuel Pump Failure Signs


You should always be aware of Overfilling which is not probably worth for your car’s engine. Usually, fuel pumps contain relief valves. So, if the relief valve of your car’s engine gets damaged, it will fail to handle the fuel flow into the car’s engine more than the necessary. In this situation, your car’s engine can be filled with more fuel. And so, after getting typically gas mileage, there could be a sudden gas hog and need emergency repair that may cost more than a hundred dollars.

Car Sputters

While driving on the road, consistent high speed is a significant symptom to identify the failure of the fuel pump. At the proper pressure, the car can suddenly occur sputtering if the pump is struggling to serve a constant fuel stream to the engine. If the engine sputtering happens, the engine struggles to maintain speeds with the demand. So, when your fuel pump is failing to supply constant fuel, the engine must cause your car to sputter.

Power Loss

When going up on hauling heavy cargo or a slope, the weakening accessories of the fuel pump starts causing problems. In such situations, a car goes under immense stress, and the pump will be unable to cope up with the vehicle’s fuel demands. This trouble leads a car to a loss of overall power.

Engine Can't Ignite

There is a solution that might be happened with almost every car owner. When you turn the car key, but your car won’t start, it must be frustrating for you. The fuel system is one of the possible reasons that can cause an issue to start your car.  A clogged fuel filter results in fuel pump failure and not allows gas to get the engine. Such power depreciation leads a car to the inability to create a spark and cause faulty ignition. 

Stalling at high temperature

Stalling usually causes due to clogged fuel injector. But, many things cause car stalling. In fact, problems with the pump for crankshaft may cause your engine to stop working. Even while you are driving, your car may create sudden noise from the engine and stop running yet. It can predict that cracks and damages cause your fuel pump to stop working. 

When the heat rises, your car can be off and cold and results in car stalling yet. Also, you should make sure the water pump is not loose, and the shaft shield is allowing the water pump to keep working. 

Pressure gauge

Each car of various models has different standards of fuel pressure. A petrol engine and a diesel engine will never prescribe the same fuel pressure yet.  Through the fuel pressure gauge, you can check the amount of fuel applied to the engine. It is used to ensure proper fuel installation. 

By checking fuel pressure indication, you can measure the fuel pressure within the engine. The pump needs immediate attention when it fluctuates and provides less signal of your fuel.

Types of Fuel Pressure

Usually, there are two types of fuel pressure in a car engine. First is the Effective (Differential) pressure, which is the fuel pressure exerted from the tank to the fuel rail, and then there is the rail pressure, which like its name, suggests the pressure maintained in the fuel rail.

The adequate pressure is of the main focus as it is the measurement of fuel flowing from the tank to the rail system.

Testing Fuel Pressure

Most modern cars would have a built-in Schrader valve so that the gauge of fuel pressure can be attached to. If the car does not have a valve, it is recommended to check the owner’s manual for guidelines. In this situation, it is essential to reduce the fuel line and join a testing adapter.

Rail pressure is the measurement of fuel flow in the rail system. It can be measured by inserting a fuel pressure sensor at the end of the rail. While it is not critical like the Effective (Differential) pressure, nonetheless, it is necessary to ensure that the fuel injectors are getting a steady flow to perform in a manner that optimizes the engine’s capacity to generate the required power.

Fuel systems

There is another factor to be included while measuring fuel pressure. The fuel system is generally two types- the return style and return less style.

In a return style fuel system, two lines are connecting the fuel tank and the rail. One is used to carry the fuel to the rail mechanically, and the other does the reverse. In a return style fuel system, there is a pressure regulator that controls the flow of excessive fuel back to the fuel tank. When the engine is running, the regulator will create suction to close the return valve and allow the rail a higher fuel pressure as the car is on the move. With the engine off, the regulator will allow the rail to maintain a steady flow and pass the excessive amount back to the tank.

The return less system has only one line connecting the fuel tank with the rail. The fuel is pumped electronically with the pump that consistently pumps fuel into the engine at a fixed rate based on the strength of the pump.

Problem with the car's fuel pressure

There are some key points to identify if there is a problem with the car’s fuel pressure.

If the fuel leaks fast, it may be because of the pump. The fuel pumps have a valve inside which are lined horizontally inside the pump. They open up when the accelerator is pressed and close down to cut off the fuel from leaking. The valves are usually the ones that get worn out and once damaged cause fuels to leak at a much higher rate.


A Slow leak might indicate that there is a problem in the fuel injectors given that the pressure regulator is checked. There are O-rings on each of the injectors that are usually the first to wear off or get damaged. In this case, the fuel overflows to the chambers bypassing the fuel injectors and cause a slow rate of fuel leakage.

What should be the fuel pressure?

When the key is turned to drive mode, the fuel pump kicks in even though the car is not ready to drive. In a conventional General Motors (GM) car, the fuel pressure should be around 48 psi to 58 psi in a direct port injection system.

What should fuel pressure be at idle?

While in idle mode, the fuel pressure should be around 35-40 psi as the fuel suction kicks off in the fuel pressure regulator as soon as the engine starts. With a steady rev of 2000rpm, the pressure should rise to about 54-50 psi and hold the same pressure, but it will go up with the sudden acceleration in comparison to the amount of acceleration.  


By having some basic knowledge on how to test fuel pressure, the hassle of facing time to time car break down in your everyday life can come in handy as well. Also, it saves up your money on getting the car checked up for simple fuel pressure at the automotive service centers. 

Along with Airflow intake and spark ignition, the fuel pressure is the key factor to keep a car’s engine running. Indeed, a regular checkup of the fuel pressure allows you to keep the car’s engine optimized to your need yet.

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