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The Top 5 Symptoms of a Bad Fuel Pressure Regulator

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Some vehicles rely on an external fuel pressure regulator to provide the appropriate fuel pressure to the engine. Like any automotive part, the regulator can eventually fail—and when it does, you’ll likely encounter one or more noticeable symptoms.

What Does a Fuel Pressure Regulator Do?

A fuel pressure regulator does what its name implies: It regulates the pressure of the fuel going to the fuel injectors.

On older vehicles with a continuous fuel system, the regulator is typically a vacuum-controlled device installed on the return side of the fuel rail. The regulator routes excess fuel back to the gas tank to maintain fuel pressure. A vacuum line connects the regulator to a source of engine vacuum, thereby allowing the regulator to vary fuel pressure according to engine load.

automotive fuel pressure regulator
As the name implies, the fuel pressure regulator regulates the pressure of the fuel going to the fuel injectors.

A vacuum-operated fuel pressure regulator can fail in several different ways. In many cases, the diaphragm inside of the regulator ruptures, allowing fuel to be drawn through the vacuum line and into the engine’s intake manifold. Such a scenario usually results in an engine that runs rich (too much fuel). A regulator that is stuck closed will also result in a rich running condition.

In other instances, the regulator may not seat properly, resulting in an engine that runs lean (too little fuel).

It’s important to note that most modern vehicles have a returnless fuel system that does not include an external fuel pressure regulator. Instead, most returnless systems use a control module to manage fuel pump speed, thereby maintaining the desired fuel pressure. There are also some designs that use an in-tank pressure regulator that’s built into the fuel pump.

Signs of a Bad Fuel Pressure Regulator (External Vacuum-Operated Type)

Over time, a vacuum-operated pressure regulator can fail—and that usually results in one or more noticeable symptoms. The most common symptoms of a bad fuel pressure regulator include:

Engine Performance Problems

A faulty fuel pressure regulator can cause a loss of fuel pressure. As a result, the engine may exhibit performance problems, such as hard-starting, rough running, stalling, and a lack of power.

Illuminated Check Engine Light

Your car’s engine computer looks for issues—including engine performance problems caused by a faulty regulator—that could lead to an increase in emissions. Usually, the device will recognize these issues, turn on the check engine light, and store a corresponding diagnostic trouble code (DTC) in its memory.

Black Smoke From the Tailpipe

A faulty fuel pressure regulator can cause the engine to run rich. In extreme cases, this condition can cause the vehicle to emit black smoke from its tailpipe.

driver starting the ignition
If a vehicle cranks but doesn’t start, it may have a faulty fuel pressure regulator.

Fuel In the Regulator’s Vacuum Line

When a regulator suffers from a ruptured diaphragm, you’ll likely find fuel in the line connecting the device to engine vacuum.

Vehicle Cranks But Doesn’t Start

A faulty regulator can prevent the engine from getting proper fuel pressure, resulting in a vehicle that cranks but doesn’t start.

Where Is The Fuel Pressure Regulator Located?

On older vehicles with multiport fuel injection and a continuous fuel system, the regulator is usually mounted in the fuel rail.

There are also some older applications that have throttle body injection (TBI) or central port injection (CPI). With TBI, the regulator is integrated into the fuel metering assembly inside of the throttle body. Vehicles with CPI have the regulator mounted to the injector assembly (sometimes called a spider unit).

Most newer vehicles have a returnless fuel system and, therefore, do not have an external pressure regulator. Instead, most returnless systems use a control module to manage fuel pump speed, thereby maintaining the desired fuel pressure. There are also some designs that use an in-tank pressure regulator that’s built into the fuel pump.

fuel pressure regulator
On older vehicles, the regulator is usually mounted in the fuel rail while most newer vehicles have a returnless fuel system and, therefore, do not have an external pressure regulator.

How Much Does a Fuel Pressure Regulator Cost?

If you choose to have a professional replace your car’s fuel pressure regulator, you can usually expect to pay somewhere between $250 and $400 to get the job done. Of course, the exact price will depend on various factors, such as the year, make, and model of your vehicle.

You can save money by replacing the regulator yourself if you have the tools and the know-how. CarParts.com has a wide variety of replacement regulators available for various makes and models.

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