Fuel pressure regulator FAQ

A fuel pressure regulator is an integral part of a vehicle’s fuel system. Most engines use a fuel pressure regulator now and there are things that can go wrong with them.

Your fuel system is designed to work within a specific range of pressure. If the pressure is out of this range then the vehicle will not run or will run inefficiently.

Fuel Pressure Regulator
Fuel Pressure Regulator

Testing the fuel pressure regulator is a simple task that requires some minor equipment and a short amount of time. Spend the money and get a good Fuel Pressure Testing Gauge. I have heard of people using a Tire Gauge, BUT Don’t, DANGER.  Average fuel pressure can be anywhere from 45 psi to 55 psi, but consult with your vehicle owner’s manual for the proper fuel-pressure range before performing this test.
There are two different problems that a bad fuel pressure regulator can cause:

Low Pressure
Most problems with fuel pressure are due to the pressure being too low. The inability of the fuel pump to increase the fuel pressure up to the vehicle’s specifications may have several causes.

  • If the pressure is too low there may not be enough fuel reaching the engine for it to start. Or, if it does start, it may not run efficiently.
  • A fuel leak is a cause of low fuel pressure, although this problem can often be identified without the need for installing a fuel pressure gauge.
  • Other problems that can cause low fuel pressure include a kinked fuel inlet line or a clogged fuel filter or strainer.
  • A bad fuel pump in the fuel tank can also prevent the fuel pressure from reaching the required level.

High Pressure
Fuel pressure that is too high can cause the engine to run too rich. Common causes of high fuel pressure include a bad fuel regulator or a clogged return line. You will need to perform two different tests to identify the reason for excessive fuel pressure.

  • The first test requires you to relieve the system fuel pressure and connect a relief hose to the fuel return line. Place the free end of the hose in a container and activate the fuel pump. The fuel return line is blocked if the fuel pressure now meets specifications. Otherwise, the fuel pressure regulator may be faulty.
  • The second test requires you to allow the engine to idle while disconnecting the vacuum hose on the fuel pressure regulator for vehicles that are so equipped. The fuel pressure regulator may be faulty if the fuel pressure does not increase by about 5-10 psi.

Too high of pressure may result in over fueling of the engine. This can lead to a rough running engine, poor fuel mileage, and black smoke coming from the exhaust If your fuel pressure regulator is going bad, your car could display several different symptoms. Get your fuel pressure regulator checked if you notice any of the following.

Fuel Fouled
Fuel Fouled

Spark Plugs Are Black

Remove a spark plug and examine the end of it. If it is sooty, it could be a sign of a bad fuel pressure regulator. If you find a plug in this condition, check the rest of them. A sooty spark plug could just mean the engine is burning oil at that head. If you end up replacing your fuel pressure regulator, you might also want to replace your plugs. They could be fouled out from the bad fuel pressure regulator. You can try simply cleaning them and putting them back, but if your engine still runs poorly, get new ones.

Rough Running Engine
Rough Running Engine

Engine Runs Rough

Speaking of poor engine performance, if you are idling the engine and it is not running smoothly, change your oil filter and check your pressure regulator to repair bad fuel pressure. Another sign that your engine is suffering the effects of a bad fuel pressure regulator is if you have trouble starting the car. It will fail to turn over a few times before it actually starts.

Black Smoke From Tailpipe
Black Smoke From Tailpipe

The Tail Pipe Emits Black Smoke

Having black smoke coming out of your tail pipe is a sure sign there is something wrong with your fuel pressure regulator. Replace it. The normal color of any smoke coming out of the exhaust should be white or gray, not black, so if you see the latter, there is definitely something wrong.

 

Gasoline Smell
Gasoline Smell

The Dipstick Smells of Gasoline

Check the oil dipstick and see if you smell fuel on it. If you do, it could be a symptom of a bad fuel pressure regulator, which has allowed gasoline to leak into the oil system.

 

Gas Out Tail Pipe
Gas Out Tail Pipe

Gasoline Drips Out of the Tailpipe

Gasoline dripping out of your tailpipe is either the result of your overfilling your tank or a bad fuel pressure regulator. Most likely, the gas is leaking into the exhaust system because the fuel pressure regulator is allowing it to pass into the lines.

Rough Running Engine
Rough Running Engine

Engine Stalls

If the engine stalls when you press down on the gas pedal, check the fuel pressure regulator. There shouldn’t be any hesitation when you press on the gas. Even if you only notice a little hesitation, get your pressure regulator checked out because it may just be starting to go bad.

Wet-Fuel-Leak
Wet-Fuel-Leak

Gasoline Is in the Vacuum Hose

If you are noticing any of the signs above, but aren’t convinced that the cause is a bad fuel pressure regulator, there is something you can do to be sure one way or the other. Remove the vacuum hose that attaches to the fuel pressure regulator, making sure the engine isn’t running. If gas is in the line, your fuel pressure regulator is bad. Also, if there is none in the line, but, when you turn the switch on, fuel drips out of the hose, it is bad.

 

We hope that this information we just provided for you helps you to understand how fuel pressure regulators work.

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