10 Symptoms Of A Bad Fuel Pressure Regulator

Just as the blood in a human is the life bank of the body, so also is the fuel in a car. Fuel is the life of a car’s engine; when fuel is mixed with air, it produces the energy that drives a car. Now, what is a fuel pressure regulator?

The fuel pressure regulator is responsible for regulating the pressure of the fuel flowing through the fuel system, just as the name implies. A fuel system is made of several components, and a malfunction in any of the components could to the breakdown of the car’s engine.

fuel pressure regulator

The fuel pressure regulator is present to make sure that the engine gets the right amount of fuel for combustion. Different engine types require varying amounts of fuel, and they can be metered by changing the fuel pressure. As complex as the fuel system, the fuel pressure regulator is very important in contributing to the system's efficiency. Any problem with it can lead to other issues within the vehicle.

This article gives an insight into the 10 symptoms of a bad fuel pressure regulator. Also, in this article, you get to learn about other issues relating to a bad fuel pressure regulator and how to handle these issues.

10 symptoms of a bad fuel pressure regulator

10 symptoms of a bad fuel pressure regulator

The symptoms of a bad fuel pressure regulator are relatively easy to notice. Once you notice any of these symptoms listed below in your car, then it's time for a replacement. Reluctance to get a new one will lead to additional problems in the vehicle as well as extra costs.

So, what are these symptoms?

Black smoke coming out of the exhaust

If there should be any smoke coming out of your exhaust, the color should be either white or grey. Black smoke is a sign of trouble and should be treated as such. A good car engine in its perfect condition should not emit smoke from the exhaust, as it shows that the engine is using the right air-fuel mixture.

Black smoke from your exhaust pipe is a symptom that the fuel regulator in your car is bad. Black smoke from the exhaust in a car also means that the carburetor is bad, that the exhaust is clogged with dirt, or in the worst case, the fuel injectors in the car have spoilt.

In some cars, the fuel pressure regulators are built into the fuel pump assembly, while in some other cars the fuel pressure regulators are placed in the fuel rail and can be checked without tampering with the whole fuel unit.

smoking car exhaust due to bad fuel pressure regulator

Fuel leakage

Fuel leaks occur when the seal or diaphragm in the fuel pressure regulator is damaged. The fuel pressure regulator has a seal on its sides, and when those seals are damaged, it creates an opening for the fuel to leak from. The seals on the fuel pressure regulator get damaged from wear and tear.

Fuel leakage

Fuel leakage is a financial strain because your car continues to gulp unnecessary amounts of fuel. But also, fuel leakage is a health hazard to you, other road users, and passengers. When the fuel in a car is leaking, the engine is not getting the appropriate amount of fuel to produce energy, so the energy will work harder to get more fuel into its combustion compartment.  Once fuel leakage is noticed, the best thing to do is to locate the source and then get a professional to help stop it.

Fuel leak

Other causes of fuel leakages are a broken fuel line, the presence of contaminants, filter problems, and corrosion.

Poor acceleration

A bad fuel pressure regulator also leads to poor acceleration, where the car does not accelerate as it should. Poor acceleration is one of the first symptoms easily noticeable when the fuel pressure regulator in a car goes bad. Poor acceleration means that the car becomes slower, and reduces in speed.

No matter how much power is exerted on the accelerator, the car will not go as fast as it used to because the fuel pressure regulator is damaged.

This happens because the damaged regulator is flooding the ignition system with surplus fuel, more than is necessary, and this creates an imbalance in the fuel-air mixture in the car. Another reason for the poor acceleration in a car is a faulty fuel injector. When the tip of the fuel injector is dirty, it clogs the small holes that supply fuel into the combustion compartment, causing the poor acceleration.

Decreased fuel efficiency

decreased fuel efficiency

The fuel pressure regulator is in the fuel system to control the pressure of fuel that gets to the engine. If the fuel pressure regulator is damaged, instantly there is an imbalance in the air-fuel mixture.

If there is very low pressure to the engine, the fuel will transfer slowly to the engine, therefore, reducing speed and acceleration. When the fuel is slow, the engine will overwork itself in a bid to get more fuel to consume.

This can also happen if there is high pressure getting to the engine. The combustion compartment will be flooded, and it leads to a decrease in fuel efficiency. Leaks in the fuel system can also lead to decreased fuel efficiency, which is another symptom of a damaged fuel pressure regulator.

Engine misfires

Engine misfires are a noticeable symptom of a damaged fuel pressure regulator. When the engine of a car misfires, it results in rough acceleration, engine vibration, and slow acceleration. Engine misfires can arise from damaged sparkplugs, a damaged ignition system, damaged vacuum lines, damaged fuel injectors.

Engine misfires occur because there is not enough fuel getting to the combustion compartment, and the engine produces odd noises like rough sounds. If ignored, this can lead to a total breakdown of the engine system in the car. Engine misfires happen differently in several car models, but a similar symptom is that the engine will produce odd noises when turned to start.

Spark plug becomes black

The spark plug in a car gives the appropriate heat element to ignite the air-fuel mixture. As mentioned earlier, the engine in a car needs the appropriate amount of air and fuel to produce power and run effectively. This power is from the controlled explosion in the combustion compartment, owing to the fuel pressure regulator in the fuel system.

An imbalanced air-fuel mixture causes black particles on the tips of the spark plug; these black particles are carbon deposits that rest on the tips of spark plugs. Not all engines need spark plus, as diesel engines do not need a spark plug.

black spark plug

Noisy fuel pump

When a car in good condition is in motion, it produces a humming sound from the fuel pump. However, if the noise becomes oddly loud and embarrassing, it means that the fuel pressure regulator in your car is bad and needs a change.

A stalling engine

An engine that won't start can be a result of many problems like a dead battery, a faulty alternator, a damaged faulty pressure regulator. If the engine won't start because of a dead battery, then the battery does not have enough power to start the car engine, including the starter.

The fuel pressure regulator balances the air-fuel pressure in the combustion compartment and a lack of this will cause the car engine to stall. If the engine goes bad because of a damaged pressure regulator, the engine will give a rough sound when turned on for some seconds, and then shut down immediately because the pressure to the engine is not enough to cause it to start. Once you accelerate your car, your car should jump to life immediately.

stalling engine

Issues during deceleration

An issue during deceleration is a symptom of a bad fuel pressure regulator. In the car engine, there is a lot of fuel getting to it and this is more than what the engine can take so this causes problems.

The bad fuel regulator will make the car take time to slow down even after your foot is removed from the pedal. This is hazardous because if you are driving at a high speed and you want to slow down, or at a sharp turn, it will take a lot of time for your car to slow down. This is a recipe for a ghastly accident, and once you notice this symptom, you should immediately attend to it by having a professional diagnose the car.

Fuel in the car’s vacuum hose

Fuel in the car’s vacuum hose

If there is a problem with a fuel pressure regulator, then fuel would leak into the vacuum hose. This is a major problem that should not be ignored because it is hazardous. To solve this issue, you can easily disconnect the vacuum hose from the regulator to remove the fuel.

Once you turn on your car’s engine, you can leave it on for some minutes to check if the fuel will get into the vacuum hose. If this happens, you can either disconnect it by yourself or get a professional to do so for you.

Checking for fuel pressure regulator fuel leaks

A fuel pressure regulator ceases to do its intended job when it

  1. Ceases to hold pressure, which does not provide enough fuel for the engine to thrive on.
  2. The fuel regulator gets stuck and builds up more pressure than is necessary. The fuel injectors then deliver too much fuel to the engine.

To test the regulator, you need a fuel pressure gauge. A fuel pressure gauge is an affordable tool and you can get it from a nearby auto shop or can be bought online.

To test for fuel leaks in a fuel pressure regulator for leaks you will need a fuel pressure gauge. To do this follow these steps highlighted below:

  1. Open the hood and check for the fuel pressure regulator located at the end of the fuel rail. It is the fuel rail that holds the fuel injectors. The fuel regulator is a small metallic cylinder with a vacuum hose on the top.
  2. Check the vacuum hose if it has a tight connection to the cylinder. If the hose is loose, it will prevent the regulator from working efficiently. Also, check for any extra damages, and then remove the vacuum line or hose from the regulator.
  3. If there are any signs of fuel in the vacuum line, then the diaphragm inside the regulator leaks, and it should be replaced.

If there are no signs of fuel in the vacuum hose, then there is no need to test for fuel leaks.

How to test a fuel pressure regulator

The test on the fuel pressure regulator differs from one car model to another. So before you embark on a test, you need to either consult a professional or use your car repair manual. The general steps involved however include the following:

  1. Locate the test valve which is in the fuel rail.
  2. Connect your fuel pressure gauge to the test valve. If the model of your car does not have this test valve, you need to check the repair manual for the best way to connect the gauge to the valve.
  3. Ascertain the fuel system pressure specification for your car with the engine running. Or you can look for the pressure number in your car’s repair manual.
  4. Start your car’s engine for a few seconds, then turn it off.
  5. While the engine is one for a few seconds, check the fuel pressure gauge. After turning the engine off, the pressure should hold for about 5 minutes.

Further steps

It is important to remove the vacuum line, while the engine is still running.

  1. Take note of the pressure gauge reading.
  2. Turn the ignition key to the ‘on’ position, but without starting the engine. This process should last for at least 5 seconds, and it should be repeated at least 5 times to ensure the fuel pressure is consistent.
  3. Compare the pressure gauge reading to the one written in your car’s repair manual. For more on pressure gauge click here.

If the pressure gauge is reading lower than the specification, while the engine is running it means:

  • A leaking fuel injector
  • A worn-out fuel pump
  • A clogged fuel filter
  • A damaged anti-drain valve
  • A damaged fuel pressure regulator

If the fuel pressure immediately drops after shutting the engine down, then the fuel pressure regulator is bad. If the reading is above the required specification, the regulator is not bad. This reading could be as a result of another problem in the car.

Common questions about fuel pressure regulators

fuel pressure regulators

How much does it cost to fix a fuel pressure regulator?

Fixing a bad fuel pressure regulator depends on the type of car you drive or the auto-mechanic shop you go to for repairs.

The average cost for replacing a bad fuel pressure regulator is between $253 and $372. The labor cost should be between $105 and $135, and the estimate of the regulator parts is between $147 and $238. These prices exclude taxes, fees, and location charges.

To fix a bad fuel pressure regulator can take up to 4 hours to do an overall job in the fuel unit. But if it is only the regulator it takes one hour.

What happens when you unplug a fuel pressure regulator?

If the fuel pressure regulator reading is low after testing, you should disconnect the vacuum hose connected to the regulator. However, if the regulator is not leaking, you should notice an increase in the pressure. An increase means you have to change the fuel pressure. If there is no change or increase, it means that the fuel pump or the fuel line is faulty.

Can a bad fuel pressure regulator cause no start?

One of the symptoms of a bad fuel pressure regulator is that the engine will misfire. But beyond that, the engine of the car will also stall and not start. Regardless of how many times you try to start the engine it will come one and go off immediately then cease power.

How can you clean a fuel pressure regulator?

To start, you need to remove the fuel pressure regulator, clean it, and then reinstall it into place. To clean your fuel gauge regulator, follow these steps carefully:

Disconnect the battery cable

Disconnect the battery cable

Disconnect the negative battery cable, and remove the manifold assembly, and the vacuum line. Remove all these parts one after another to avoid damages.

Remove the retaining bracket

In this process, you carefully remove the fuel pressure regulator retaining screw and the retainer bracket.

Remove the o-ring

Carefully use a piece of rag to clean any fuel spillage and then pull the regulator from the fuel rail. After removing the regulator, also remove the o-ring from the vehicle.


After removing all these parts, you use another piece of rag or cloth to clean the parts removed. Clean them carefully to avoid damages of any sort.

Reinstall all the parts

After cleaning all the parts, your fuel pressure regulator is ready for re-installation. Follow the same process in which all the parts were removed. After fitting your regulator is clean.


Some fuel pressure regulators are built into the fuel pump assembly, while other pressure regulators are put in the fuel rail. You can fix it along with disassembling the whole fuel pump unit. The symptoms listed above are easily noticeable, and once you notice the slightest change in your car, your next stop should be the auto-repair shop.

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