A fuel pressure regulator is an integral part of a vehicle's fuel system. It is located between the vehicle's gas tank and its carburetor. It is designed to keep the fuel line pressure at a consistent value, allowing for smooth operation of the engine.
Too much fuel entering a vehicle's engine is known as a "rich" condition, while too little fuel is known as a "lean" condition. If the vehicle is running rich, a flap in the fuel pressure regulator will close and allow the excess fuel to flow back to the gas tank. If the vehicle is running lean, the flap will open the fuel pressure regulator, allowing more fuel to flow to the engine.
Average fuel pressure can be anywhere from 45 psi to 55 psi, but consult with your vehicle service manual for the proper fuel-pressure range before performing this test.
Step 1 - Locating the Fuel Pressure Regulator
Finding the fuel pressure regulator is not that difficult. Follow the fuel line to the throttle body or carburetor. The regulator is most likely attached near the throttle body assembly.
Step 2 - Testing the Vacuum Line
You first need to test the vacuum line leading into the fuel pressure regulator. Remove the existing vacuum hose and replace it with clear plastic tubing. Start the vehicle and manually open the butterfly valve on the carburetor, or have a friend press on the gas pedal. A leak in the regulator will allow fuel to escape into the line. The clear plastic tubing will allow you to see this happening.
If the vacuum system is working properly, replace the plastic tubing with the original vacuum hose and continue troubleshooting.
Step 3 - Testing the Fuel Pressure Regulator
If your vehicle's fuel pressure regulator has a port available for the regulator gauge, you can screw the gauge into the regulator for this test. If no port is available on the regulator, there should be a location along the fuel rail assembly where you can attach the tester. Look for a screw cap assembly along the fuel line. Unscrew the cap and screw the regulator gauge in place.
Once the gauge has been installed, turn the key to the on position and read the indicator on the gauge. It should read the correct fuel system pressure for your vehicle. Have someone else start the car while you continue to watch the gauge indicator. The indicator should increase by 5 psi. If the fuel pressure does not increase, the fuel pressure regulator is faulty and needs to be replaced. A decrease in the pressure is an indication of a clogged fuel filter or faulty fuel pump and further troubleshooting of those parts is necessary.
Step 4 - Finishing the Testing
After testing your fuel pressure regulator, remove the fuel pressure gauge and reattach the screw cap to the regulator testing port or the fuel line assembly. Pick up any necessary parts for your repair and replace them according to your car's specifications. Faulty fuel delivery can lead to problems in the engine, which will be much more costly to repair.