The fuel pressure regulator maintains the right amount of pressure that your car’s injection system needs to pump sufficient gas.
But if you notice black smoke, engine misfiring, or fuel leaking from the tailpipe, your regulator could be failing.
Read on to better identify bad fuel pressure regulator symptoms, so you can spot and fix them ASAP. We’ll also learn how to diagnose a failing regulator and the costs of replacing one.
This Article Contains:
- Top 10 Bad Fuel Pressure Regulator Symptoms
- How to Test a Faulty Fuel Pressure Regulator?
- How Much Does Replacing a Fuel Pressure Regulator Cost?
- 4 FAQs on Fuel Pressure Regulators
Top 10 Bad Fuel Pressure Regulator Symptoms
Here are the two major problems with a bad fuel pressure regulator:
- Low fuel pressure or running lean: Less fuel and more air
- High fuel pressure or running rich: Less air and more fuel
These conditions then create additional issues in the engine, exhaust, or fuel system:
A. Engine Performance Issues
Some signs indicating a fuel pressure regulator problem (FPR) include:
- Engine misfire and low acceleration power: Normally, fuel system parts work with the FPR to provide sufficient fuel at the right time to increase the car’s speed. But if the FPR is faulty, you may notice your engine losing power when driving or a lag between engaging the gas pedal and an increase in speed.
- Engine won’t start: A faulty fuel pressure regulator may not deliver the necessary pressure to fuel injectors — meaning your engine won’t receive sufficient fuel. Without proper fuel pressure, the engine will either strain to crank from a lack of gas or the combustion chamber will flood with excess fuel.
Note: A malfunctioning fuel pressure regulator also causes rough idling, stalling, and sputtering.
- Illuminated check engine light: Your cars’ computer systems can detect engine performance problems, like a misfire, and trigger the check engine light in response.
Note: Since many issues trigger the check engine light, you won’t immediately know if you have a faulty fuel pressure regulator. Get a mechanic to check the diagnostic code to see if the regulator has triggered the dashboard light.
B. Exhaust and Emission Issues
Here’s how a bad regulator can affect the car’s exhaust:
- Black smoke from the exhaust: If the fuel pressure is too high, the injectors will send excess fuel to the chamber. This results in incomplete combustion, producing black smoke when it burns.
- Fuel dripping from the tailpipe: When extra fuel is pumped by the fuel injector, it stays in the chamber without burning. The additional fuel can drip out of the exhaust pipe.
- Engine backfires: When a bad regulator allows extra fuel into the engine, not all of it burns up before the exhaust valves open. This creates a fuel leakage into the exhaust headers, where it combusts, and the engine backfires (fire comes out from the exhaust).
C. Fuel System Issues
When it comes to your fuel system, here’s how symptoms of a bad fuel pressure regulator manifest:
- Fuel leakage: When the diaphragm or seals on fuel pressure regulators break, you’ll experience a fuel leak. That fuel leak will likely emit a strong fuel smell.
- Fuel in the vacuum hose: The vacuum hose helps maintain negative pressure (vacuum) within your car. However, when the diaphragm breaks, fuel leaks into the vacuum hose.
- Reduced fuel efficiency: High pressure floods the combustion chamber with fuel and wets the spark plugs. Meanwhile, low fuel pressure means there’s insufficient fuel supply. If this air-fuel ratio is unbalanced, your engine will overwork, resulting in reduced fuel efficiency.
- Noisy fuel pump: Usually, the pump hums when drawing gas from the fuel tank. But if the pressure is low, the fuel pump will strain to draw the fuel, resulting in a loud whining sound.
But how can you be sure that your car has a bad fuel regulator?
Let’s find out.
How to Test a Faulty Fuel Pressure Regulator?
You first need to locate the fuel pressure regulator, which depends on your vehicle’s make and model:
- In older cars with return-style systems, the FPR (a metallic cylinder) is located near the fuel rail with one vacuum hose (vacuum line) on the top.
- In newer cars with returnless fuel systems, the regulator is located inside the fuel tank near the pump. The powertrain control module (PCM) works with the fuel pressure sensor and regulator to maintain the pressure.
As finding and testing the FPR requires some technical experience, it’s best to hire a professional to diagnose a fuel pressure regulator failure.
Here’s how a mechanic will test the bad fuel regulator:
- The mechanic will first park your car in a well-ventilated area, and wear safety goggles and gloves.
- They’ll depressurize the fuel system and remove the engine shields.
- Your mechanic will disconnect hoses or other parts to access the fuel pressure regulator.
- Then, they’ll connect a fuel pressure gauge to a port or Schrader valve (used to check and release fuel pressure) on the fuel rail.
- Next, the mechanic will turn on the car and let it idle. After a while, they’ll turn the engine off.
- They’ll refer to your car’s manual to check and compare the fuel pressure readings. The fuel pressure should hold for approximately five minutes.
- If the pressure is constantly low or high then the air-fuel ratio is not changing as it should, signaling a fuel pressure regulator failure.
Note: The testing steps may differ slightly based on the location of your fuel regulator. However, your mechanic will use the fuel pressure gauge to check the readings regardless of location.
Based on their inspection, the mechanic will repair or perform an FPR replacement.
Let’s look at some related costs.
How Much Does Replacing a Fuel Pressure Regulator Cost?
To replace a malfunctioning FPR, you’ll have to spend between $260 and $330.
The costs include:
- Parts: $160 and $200
- Labor: $100 and $130
Wondering if there’s more to fuel pressure regulators?
Then check out these FAQs to learn more.
4 FAQs on Fuel Pressure Regulators
Here are a few common queries people ask regarding FPRs.
1. How Does a Fuel Pressure Regulator Work?
When you start your car, the fuel pump pushes the gas from the tank. The fuel line carries the gas to the fuel rail, eventually reaching the regulator. Inside the regulator, a diaphragm, spring, and bypass valve work together to maintain optimal fuel pressure.
But what’s the optimum fuel pressure?
Most car engines require fuel pressure between 4 and 7 psi (pounds per square inch). However, high-performance fuel-injected engines may require pressure as high as 60 psi.
If this pressure exceeds the set limit, the diaphragm compresses the spring to open the bypass valve and let the excess fuel flow back to the tank. But if the pressure is low, the spring keeps the valve closed to maintain the necessary fuel pressure for optimal engine performance.
By keeping this pressure in check, the regulator ensures the correct amount of fuel enters the combustion chamber for ignition. When you press the gas pedal to accelerate, the regulator adjusts the pressure and allows more fuel into the fuel injector.
2. Can I Drive Without a Fuel Pressure Regulator?
No, you can’t.
That’s because most cars have an electric fuel injection system (EFI system), which includes the fuel tank, pump, rail, and injectors.
Without the fuel pressure regulator, the amount of fuel through the fuel rail to the fuel injectors (and subsequently, the combustion chamber) won’t be controlled. Eventually, your engine may not start due to improper fuel quantity.
3. How Long Do Fuel Pressure Regulators Last?
There isn’t a precise estimate, but you should schedule checks every five years and perform routine maintenance to keep the regulator in the best condition.
4. How to Maintain Your Car’s Fuel Pressure Regulator?
Here’s what you need to do to extend the lifespan of your FPR:
- Check the regulator at sufficient intervals for signs of wear and tear.
- Schedule inspections regularly to look for fuel leaks or a damaged vacuum line.
- Replace the fuel filter frequently to prevent dirt accumulation in the system.
Fix Fuel Pressure Regulator Woes with AutoNation Mobile Service
The fuel pressure regulator helps maintain the proper fuel pressure and provides the engine with the right amount of fuel to function. But if you notice engine misfires, poor fuel economy, or black smoke, then your FPR needs inspection.
That’s where AutoNation Mobile Service comes in.
We’re a mobile auto repair and maintenance solution offering a 12-month | 12-000 mile warranty on all repairs.
Have FPR or fuel system issues? Let us help you.
Need a fuel pressure sensor, MAF sensor, or oxygen sensor replacement?
We’ve got you covered, too.
Contact us to have your car checked and repaired right from your driveway.