Top 9 Bad Fuel Pressure Regulator Symptoms

Bad Fuel Pressure Regulator

Contrary to what you might have heard, the fuel pressure regulator doesn’t keep fuel pressure constant. It considers the atmospheric pressure, manifold pressure, and boost to maintain a defined pressure flowing to your car’s engine.

What happens if a fuel pressure regulator goes bad? There will be uneven fuel pressure in your engine, which may result in hard starting, rough running, poor engine performance, and other problems you wouldn’t want to experience.

So, how do you know if you need a new fuel pressure regulator?

Causes of Bad Fuel Pressure Regulator Video

Bad Fuel Pressure Regulator Symptoms

You must know that your fuel pressure regulator plays a significant role in maintaining balance in your car's engine.

Faults on the tool will not only affect the regulation of fuel pressure but also impact the core functionalities of your car’s internal combustion system. This will affect the power delivery and mileage and, in extreme cases, might set your car on fire.

The useful thing about bad fuel pressure regulators is that there are signs to show you that something is wrong. As a good driver, understanding the symptoms of a bad regulator helps you figure out when there is a need to change them.

Here are nine common symptoms of a bad fuel pressure regulator.

1. Engine Malfunction

One of the first symptoms of a bad fuel pressure regulator is that your engine starts misbehaving. The fuel pressure regulator ensures that the proper amount of fuel is sent to your engine. This required pressure is necessary to start your engine.

When your fuel pressure regulator is faulty, there is a reduced amount of pressure in the fuel rail and an imbalanced air-fuel ratio.

This sends an improper mixture to your engine. In this case, your engine might not only fail to start, but it will also misfire and backfire. It can worsen to engine knocking, hard start, or your engine will fail to start.

Cases of engine knocking are more common in diesel engines than gas engines. Misfires happen because less fuel is getting to the combustion chambers.

You will notice some odd sounds and vibrations in your engine when this happens. You should check your engine if you notice any unusual occurrences.

2. Reduced Acceleration & Deceleration

With a bad fuel regulator, your car will start losing acceleration. No matter how hard you hit the gas pedals, your car wouldn't reach maximum power.

You will experience sluggish and slow rides. The reduced acceleration on your car is because your vehicle is either running on a rich or lean fuel mixture.

A good fuel mixture shouldn’t be too rich or too lean. When it falls into any of these categories, your car will drop in acceleration and run slowly.

Bad fuel pressure regulators lead to deceleration because the engine has an excessive flow of gasoline. The unregulated pumping of fuel causes the engine to take more fuel than it can handle.

This might keep your car running without slowing down, even after you’ve removed your feet from the gas pedal.

3. Black Smoke From the Exhaust

Bad fuel pressure will result in too much smoke coming out from your exhaust. This is because you are running on oil that is too rich, and your engine is burning a lot of fuel.

The burning of excessive fuel causes the emission of black smoke from your exhaust tailpipe.

4. Fuel in Vacuum Hose

Your vacuum hose is directly connected to your fuel pressure regulator. The role of the vacuum hose is to keep air, fuel, and spark working at equal pressure.

Your fuel pressure regulator is leaking if you find traces of fuel in your vacuum hose. Take out the vacuum hose and look into it. If there is any sign of fuel in it, check the regulator immediately.

5. Faulty Fuel Pumps

The fuel pump is responsible for supplying fuel to the engine. In this process, the fuel must pass through the regulator.

Certain factors might cause a fuel pump to start making loud noises. A bad fuel pressure regulator is one of them.

Let's assume you don’t know the correct sound of a fuel pump. A good fuel pump lets out a quiet hum when you turn on the ignition. The gentle hum indicates a proper flow of fuel to the engine.

A bad fuel pressure regulator will interrupt that free flow. This interruption will cause loud noise in the fuel pumps or even damage.

The noise will increase when you accelerate the car. If you are not convinced that the loud noise is because of a bad fuel pressure regulator, you should visit a technician for a thorough check on your fuel system.

6. Soot-Covered Spark Plugs

There are no spark plugs in diesel engines. So, this symptom is unique to gas engines. With a rich fuel-air mixture running through your engine, black carbon deposits or soot will start building up around the tip of the spark plug of your engine.

This works two ways: it can either indicate that you have a bad pressure regulator, or your fuel injector is leaking.

7. Improper Fuel Flow and Efficiency

When your fuel regulator goes bad, you will have an improper fuel flow, which will affect your fuel economy. This is because an unregulated fuel pressure is moving to your cylinders.

When the flow is low, your cylinder will lack the right amount of air mixture. When the fuel is greater, your car increases its fuel consumption, negatively affecting your gas mileage.

Too much fuel pressure can also flood your engine’s combustion chamber. This will result in fuel inefficiency.

8. Exhaust Leaking Fuel

When your exhaust is leaking fuel, this is a dangerous symptom of bad fuel regulators. You must notice this on time.

Fuel leaks occur because the diaphragm of your fuel pressure or any of its seals does not hold firmly.

Rich fuel mixture runs to the exhaust pipe from the cylinder. When this happens, fuel will start leaking to your exhaust tailpipe. You should look out for any smell of fuel and fix the issue before it turns into a fire hazard.

9. Check Engine Light Comes On

Dashboards are every driver’s companion; they pass along information you might be too busy to notice. You should check your fuel pressure regulator if your “check engine” light is on.

There are a lot of factors that might trigger your sensors and monitoring system to release a signal. If you are using an older car model, you might have to run an extensive check on your engine to know where the fault is coming from.

Your fuel pressure regulator might not be the only bad item in the box. New model cars will generate error codes that will tell you exactly what the problem is.

What Is The Difference Between Lean and Rich Fuel Mixture?

A lean fuel mixture has more air than fuel. A rich fuel mixture has more fuel and less air. For a good combustion process, cars must run on the correct air-fuel ratio.

The ideal air-fuel ratio differs for different fuels. Gasoline cars should maintain a 14:7:1 air-fuel ratio.

Where Is The Fuel Pressure Regulator Located?

The fuel pressure regulator is attached to the manifold, located in your fuel pressure rail. You can identify your fuel pressure regulator at the end of the fuel, just after the fuel injectors.

The position of the fuel pressure regulator might differ for different cars. In some vehicles, they might be in the tank, and in some older car models, you wouldn’t find a fuel pressure regulator. This is because they use carburetors.

Is There a Way To Test a Fuel Pressure Regulator?

Yes, there is. You can test your fuel pressure regulator with the vacuum pump or pressure gauge.

To test your fuel pressure regulator with a pressure gauge, locate your fuel pump relay in your engine’s fuse box. Remove the fuel pump relay, and identify your Schrader valve.

Turn on your car and turn off the engine after the pressure goes to the rail. Connect your pressure gauge firmly to the Schrader valve, and ensure that there are no leaks. Put the fuel pump relay back into the fuse box, and start your car again.

Record the pressure readings when the car is running and when it is idle. You have to check if the readings are within the car’s specifications. While the engine is in idle mode, you can remove and fit back the vacuum hose and check if there is a PSI increase.

You can snap the throttle to be sure that there is an increase in the PSI readings. A good fuel pressure regulator will control pressure regulation at least 10 PSI.

What Does A Bad Fuel Pressure Regulator Sound Like?

A bad fuel pressure regulator makes disturbing noises. It usually comes with a whirring sound that might be coming from your fuel pump.

Naturally, a good fuel regulator should maintain a gentle hum. If there’s any sound other than the hum, you might be running on a bad fuel pressure regulator.

Can a Fuel Pressure Regulator Be Cleaned or Fixed?

Yes, you can clean your fuel pressure regulator, but I will advise against trying to fix it. Your fuel pressure regulator might be clogged, and it needs to be cleaned.

However, you should know that you shouldn’t clean your pressure regulators as you will do to other parts of your car. Do not clean a fuel pressure regulator with compressed air or a solvent bath.

Some regulators are difficult to clean, or you might damage them in the process. You should get a new one.


The symptoms of a bad fuel pressure regulator might vary for gas and diesel engines. However, you shouldn’t allow the defect to linger for very long. Some regulator damages will expose you to greater hazards or even accidents.

Are you noticing some of these symptoms in your car? Test your fuel pressure regulator to know if it is still functioning properly or take it to a technician for repairs.

Don’t try to fix the regulator yourself or adjust them to meet your needs. Getting a new fuel pressure regulator is a better option.