The average car owner knows how to handle a dead battery and even a flat tire, but what about fuel system issues? Your fuel system runs from the rear of your car at the fuel tank up to the fuel injectors in the engine. It controls your engine’s performance and many other components that can malfunction over the life of your vehicle. One of the lesser-known components of your fuel system is the fuel pressure regulator. When your fuel pressure regulator goes bad, you can experience symptoms ranging from poor fuel economy up to your vehicle not starting at all. We will look at the symptoms of a bad fuel pressure regulator and what it costs to have yours replaced.
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Symptoms Of A Bad Fuel Pressure Regulator
A vehicle running smoothly with no issues is a sign that your fuel system is in good working order. A specific fuel mixture ensures proper combustion and fuel efficiency to keep your vehicle running smoothly. When a fuel pressure regulator starts to fail or goes bad, you will begin to notice drivability issues, poor fuel economy, and even a no-start condition. Let’s look at some of the most common signs of a bad fuel pressure regulator.
#1. Black Smoke From Tailpipe
One of the most visual symptoms of a bad fuel pressure regulator is black smoke coming from your vehicle’s exhaust. Black smoke from your exhaust system is a sign that your engine is burning too much fuel. This is known as “running rich” and results from too much fuel burning off, creating black smoke. Black smoke coming from your exhaust pipes is hard to miss, and you can usually notice a strong gasoline smell as well. This is one of the easiest ways to tell if you have a problem with your fuel system.
#2. Engine Backfires
Initial symptoms of a failing fuel pressure regulator or other fuel system issues are engine misfiring or backfiring. Engine backfiring sounds like a loud pop, similar to a gunshot. You will also notice that your vehicle may jerk or run poorly. Engine backfiring is typically heard during deceleration. This is due to unburned gas burning in the exhaust system. A faulty fuel pressure regulator may be allowing too much fuel into the combustion chamber, and it is getting ignited in your exhaust pipes.
#3. Poor Fuel Economy
Your vehicle runs efficiently due to your engine components working simultaneously to maintain a proper air/fuel ratio. When your fuel pressure regulator malfunctions, your air to fuel mixture can be thrown off. If the fuel in your engine is no longer regulated, you could be getting more or less fuel than you need for the air flowing into your engine. This will lead to poor fuel economy and less than stellar performance, similar to the symptoms of a bad air filter. Watch your fuel mileage for any unexpected decreases, as this could be a sign of a bad fuel pressure regulator.
#4. Fuel Leaks
The fuel pressure regulator is going to consist of a diaphragm and seals that can fail over time or from not using good quality gas. This can cause the diaphragm and seals to erode and leak fuel. A leaking fuel pressure regulator is not only a safety hazard; it also directly affects your engine’s performance. It’s relatively easy to find a fuel leak by following your fuel lines, checking your fuel pressure regulator and fuel rail for leaks. Once you get closer to the fuel leak, you should start to smell strong hints of gasoline.
#5. Fouled Spark Plugs
The spark plugs in your vehicle can be found in the combustion chamber and are the source of ignition between air and fuel. When your fuel pressure regulator goes bad, your air to fuel ratio can get thrown off, causing your vehicle to run rich. Excess fuel burns in the combustion chamber when your car’s engine is running rich, causing your spark plugs to foul out due to the improper mixture. Burnt or black spark plugs usually confirm this.
#6. Fuel In Vacuum Hoses
The vacuum lines that run along your engine bay connect directly to the fuel pressure regulator. The fuel pressure regulator’s diaphragm operates with the increase or decrease of engine vacuum, so it will need a source of vacuum connected to it. When your fuel pressure regulator fails, you can end up with fuel in your vacuum lines or hoses. Removing your vacuum line and checking for fuel is a quick and easy check to diagnose a faulty fuel pressure regulator.
#7. Loud Fuel Pump
Fuel pumps can be noticeably loud, depending on the vehicle. If you have ever turned your key to the ON position and heard a humming noise for a second or two near the rear of your car, you most likely heard your fuel pump. You may also notice the same type of noise when your vehicle is under load, such as steep acceleration when climbing a hill or pulling a trailer. This could be your fuel pressure regulator starting to malfunction.
#8. Engine Misfires
Similar to your engine backfiring, a faulty fuel pressure regulator can cause a misfiring engine. Since your engine relies on the right amount of air and fuel to combust at the spark plug, a lack of either will cause your engine to run rough. When your fuel pressure regulator goes bad, the amount of fuel your engine gets will decrease while the amount of air stays the same. This can cause your engine to misfire and your car to run poorly.
#9. Poor Acceleration
To accelerate your vehicle, your air and fuel ratio needs to be adjusted for additional performance. As your throttle body opens up, your fuel system will need to adjust for the increase in airflow to keep your vehicle running smoothly throughout the RPM band. When your fuel pressure regulator cannot keep up with the demand required during acceleration, your vehicle may sputter, misfire, or accelerate slowly. Poor acceleration could come from a clogged catalytic converter as well. You can use a quality catalytic converter cleaner to resolve a clogged cat.
#10. Engine Won’t Start
A no-start condition can be the result of various components failing. This can be anything from a dead battery that needs to be jump-started to a seized engine that needs to be replaced. If your engine does not start due to a failed fuel pressure regulator, you are in luck, as it is a relatively simple and affordable repair.
#11. Check Engine Light
A check engine light is never a good sign. Similar to a no-start condition, various components can cause a check engine light. A malfunctioning fuel pressure regulator is just one of the many reasons your check engine light can come on. If your CEL illuminates, take your car to a trusted mechanic that can check your car’s computer for fault codes — this is also the quickest way to determine if your fuel pressure regulator is the culprit.
What Is A Fuel Pressure Regulator?
A fuel pressure regulator is a vacuum-operated, spring-loaded diaphragm that allows your vehicle’s fuel system to maintain constant fuel pressure. The fuel pressure regulator is commonly found at the end of the fuel rail in mechanical return systems and the fuel tank in return-less fuel systems.
The fuel pressure regulator is open at idle to allow fuel to bypass the fuel delivery system and go back into the tank. When the engine is under load, it produces more vacuum, closing the diaphragm. This allows an increase in fuel volume to the fuel injectors while keeping your fuel pressure consistent.
How Your Fuel Pressure Regulator Works
A fuel pressure regulator contains a diaphragm that controls the bypass valve, commonly referred to as a “ball seat,” which opens and closes to adjust itself for continuous fuel delivery, even during dramatic changes in fuel demand.
The diaphragm attached to the bypass valve opens when pressure (boost) is applied at the top of the regulator. When pressure is applied (vacuum/boost), a spring forces the diaphragm down, which helps to reduce the amount of excess fuel your engine uses. Your fuel pressure regulator adjusts the fuel pressure against the air pressure/boost to ensure that your fuel injectors maintain the perfect fuel and boost ratio before sending fuel to the combustion chamber.
Cost Of Replacing A Faulty Fuel Pressure Regulator
The cost of replacing your fuel pressure regulator can run you about $150 to $350 in most cases; however, if you have an electronic fuel pressure regulator, you can end up paying over $500. Most of the cost will come from the labor itself, as the cost of fuel pressure regulators is relatively cheap. The labor cost will vary from vehicle to vehicle, as some regulators are more challenging to get to than others. Take your vehicle to a reputable repair shop or dealership to get an accurate quote on replacing your fuel pressure regulator.
The Bottom Line
Now that you know the symptoms of a bad fuel pressure regulator, you should be able to identify when your regulator needs to be replaced. The fuel pressure regulator is essential to keeping your vehicle running correctly. Keeping up with preventative maintenance such as using high-quality fuel and replacing your regulator at manufacturer-recommended intervals can help prevent failure. If you are experiencing any of the symptoms mentioned above, we recommend taking your car to a trusted mechanic that can diagnose your fuel pressure regulator for issues.
Frequently Asked Questions
How do you test a fuel pressure regulator?
When you start to experience the symptoms of a bad fuel pressure regulator, testing the fuel pressure regulator can help to narrow down your issue. You will need a fuel pressure gauge to test the fuel pressure regulator.
Step 1: Locate the Schrader valve on the fuel rail. You may have to consult your manual or conduct a quick online search to find yours.
Step 2: Connect your fuel pressure gauge to the Schrader Valve. For vehicles without this service port, refer to your user manual on how to test your fuel pressure gauge.
Step 3: Find the manufacturer’s specifications for fuel pressure on your specific engine. This can be found in your car’s service manual.
Step 4: Start the car and let it idle. If the car does not start, have someone crank the engine for a few seconds. Then turn the engine off.
Step 5: Note the fuel pressure with the engine running and after shutting off. The fuel pressure should be at manufacturer specs with the engine running and after turning the car off. After cutting off the car, fuel pressure should be at manufacturer specs for about 5 minutes.
Suppose the pressure is lower than the recommended specifications while the car is running. In that case, you could have a leaking fuel injector, fuel pump malfunction, clogged fuel filter, or a bad fuel pressure regulator.
If the pressure drops as soon as the car is turned off, you could have a leaking injector, a leaking anti-drain valve in the fuel pump, or problems with the fuel pressure regulator.
Your fuel pressure regulator is likely bad if pressure is higher than specifications.
Will a car start with a bad fuel pressure regulator?
When a fuel pressure regulator goes bad, you can have a start and a no-start condition. For vehicles that still start with a bad fuel pressure regulator, rough idle and poor drivability may be experienced. Your vehicle may experience stalling if the fuel system cannot keep up with the fuel demand needed to keep the car running. Cars that do not start due to a bad fuel pressure regulator may turn over but not fully start, depending on the amount of fuel the faulty fuel pressure regulator can regulate.
What causes fuel pressure regulator failure?
Dirty fuel, lack of fuel, and old age can cause fuel pressure regulator failure. Fuel pressure regulators contain a valve that opens and closes to regulate the amount of fuel that goes to your engine. If your fuel is dirty or full of contaminants, it can cause corrosion or buildup within the fuel pressure regulator. This causes the valve to become stuck or open, hindering the regulator’s performance. While fuel pressure regulators do not have a maintenance schedule, a regulator could fail simply due to old age.