10 Symptoms of a Bad Fuel Pressure Regulator (& Diagnosis)

A bad fuel pressure regulator can cause many different symptoms. Here is a list of the 10 most common ones

Symptoms of a Bad Fuel Pressure Regulator

A faulty fuel pressure regulator is a ubiquitous part that causes a lot of engine problems.

But luckily, it’s not an advanced part to replace, you can often do it yourself, and it’s usually pretty cheap.

A faulty fuel regulator means that the air-fuel mixture will be disturbed, and the engine does not produce enough power.

In this article, you will learn the most common symptoms of a bad fuel rail pressure regulator, the location, and how to replace it. Let’s begin by taking a quick look at the signs you should look for.

The most common symptom of a bad fuel pressure regulator is a misfiring engine and a check engine light on your dashboard. You may also notice issues like decreased engine performance, fuel leakage, and black smoke coming from the exhaust pipe.

This list may still leave you with some questions. Luckily, here we have a more detailed list of the most common symptoms of a bad fuel pressure regulator:

Bad Fuel Regulator Symptoms

1. Engine Misfires

car misfires

One of the first and most common signs of all bad fuel pressure regulator symptoms you will notice is that the engine starts to misfire on idle or during acceleration.

Misfires can pretty easily be recognized. If you hear that the engine is sputtering or does not sound like usually when you are accelerating, it may be misfiring you hear.

Misfires can also be caused by a lot of other things so you should not replace the fuel regulator as soon as you notice misfires.

2. Loss in Acceleration

car acceleration

Like it sounds, the fuel regulator controls the fuel pressure. If the fuel pressure is faulty, your engine will run with a too rich or too lean mixture.

Both a too lean or an overly rich air-fuel mixture will cause a drop in acceleration. Therefore, if your car is feeling slower than before, it may be a problem with the fuel pressure regulator.

3. Check Engine Light

check engine light on dashboard e1609869927250

Almost all modern cars use a full-time monitoring system to monitor the car engine’s car sensors constantly. If one of these sensors fails, an error code is stored in the error code memory, and if this happens repeatedly, the check engine light is displayed on your dashboard.

Most car models have a fuel pressure sensor that controls the fuel pressure in the fuel rail. If the fuel regulator is faulty and the pressure gets too high or too low – the check engine light will appear on your dashboard.

4. Fuel Leakage

fuel leak

Another common symptom when the fuel pressure regulator goes bad is fuel leakage, which causes performance problems and leads to a bad smell. A fuel leak occurs when the fuel regulator’s diaphragm or external seal is damaged and fails.

Fuel leakage is also hazardous because it can cause your car to catch on fire and should therefore immediately be taken care of.

5. Black Smoke from the Exhaust Pipe

black smoke from exhaust

Black smoke is caused when your air-fuel mixture is too rich, which definitely can be caused by a faulty fuel pressure regulator.

Black smoke coming out of the car’s exhaust pipe may have various other causes, but if you see black or gray colored smoke and also notice other symptoms mentioned in this article, the problem is most likely with the fuel regulator.

6. Spark Plug Covered with Black Debris

sooty spark plug

If your engine is running too rich, caused by a faulty fuel pressure regulator, there is a significant risk that your combustion chamber will be full of soot.

Check the end of your spark plug to see if black soot has settled. If so, your fuel regulator is most likely damaged, and you will need to replace both the fuel pressure regulator and spark plug.

7. Engine Backfires

backfire

A faulty fuel pressure regulator will cause excess fuel to flow through the lines, and the engine will not be able to combust all of it, and therefore it will overfill the exhaust system.

When the fuel then gets ignited in the exhaust system because of the heat – you can hear it as loud bangs from your exhaust pipe.

This is quite dangerous and can cause your exhaust pipe to explode and your car to catch on fire.

8. Vacuum Hose filled with gasoline

car vacuum hose

A defective fuel pressure regulator diaphragm can cause the fuel pressure to go into the vacuum system. This will cause the vacuum hose to be filled with gasoline.

To check this, remove the vacuum hose connection to the fuel regulator and check whether gasoline is in the line. If so, you have a defective fuel pressure regulator.

9. Gasoline Smell from the Dipstick

engine oil dipstick

If you are driving for a long time with a bad fuel pressure regulator, it can with time fill up your engine oil with fuel.

To check this, you can lift the engine oil dipstick to check the level, and if you can smell gasoline on the dipstick, it may mean that your fuel pressure regulator has a problem.

10. Drop in Mileage

bad fuel consumption

Faulty fuel pressure can not only cause a rich mixture – it can also cause a lean air-fuel mixture. While you think a drop in mileage may be useful, it can actually damage your car engine seriously over time.

A lean mixture will often cause your car to drop in acceleration also, but if it is just slightly, the only symptom you may notice is a drop in mileage.

Fuel Pressure Regulator Location

fuel pressure regulator location

The fuel regulator is most commonly close to the intake manifold in most cars located on the fuel pressure rail.

Some car models have the fuel pressure regulator in the fuel tank near the fuel pump, and this will cause it to be much more difficult to reach and replace.

Diagnosing a Fuel Pressure Regulator

diagnose car

The best way to check the fuel pressure regulator for leaks is with a fuel pressure gauge. This test checks whether the fuel pressure regulator regulates the line pressure appropriately according to the engine vacuum changes.

Let the engine run and disconnect the vacuum hose from the regulator. When the hose is disconnected, the fuel system’s pressure should increase by 8 to 10 psi. If there is no change, this means that the pressure regulator is defective and must be replaced. Find more information here: Testing a fuel pressure regulator.

You should also check that the pressure is within the manufactures specifications. You can usually find these in a repair manual for your car.

On newer vehicles, the fuel pressure regulator can be conveniently checked with an OBD2 scanner in any garage or at home, but it is always a good idea to check it manually as well. If you are interested in an OBD2 scanner for use at home, you can take a look at our overview article: OBD2 scanner review.

If you do not have a fuel pressure tester at home but want one, you can check it out here on Amazon: Fuel pressure testerir?t=askamastermec 20&l=am2&o=1&a=B078PFSRZT .

If you diagnosed the fuel pressure regulator and you found it faulty, you can find more information about replacing it in our guide: Fuel pressure regulator replacement cost.

FAQ

How do you fix a fuel pressure regulator?

Most fuel regulators are sealed and not repairable. In some older fuel regulators, you could replace the internal parts, but it is rare nowadays. However, fuel pressure regulators nowadays are often quite cheap.

What does a fuel pressure regulator do?

The fuel regulator is doing exactly what it sounds like. It regulates the fuel pressure in the fuel rail with help of the pressure in the intake manifold. It increases the pressure on higher RPMs and lowers the fuel pressure at idle.

Can a bad fuel pressure regulator cause no start?

If the fuel regulator is so bad that the fuel pressure will be very low, it can cause no start. Also, if an internal leak is filling the vacuum lines with fuel, it can cause it not to start anymore.

How long does a fuel pressure regulator last?

A fuel regulator can often easily last the lifetime of the car. It is not very common that the fuel pressure regulator fails on most car models. However, it can sometimes happen, but there is no fixed time or mileage when you should replace it.

Written by:

Magnus is the owner and main author of MechanicBase. He has been working as a mechanic for over 10 years, and the majority of them specialized in advanced diagnostics and troubleshooting. He has also been a motorsport (drifting) driver for over 5 years.