How to Test Fuel Pressure Regulators

Fuel pressure regulators are critical to proper performance of any vehicle engine. If it is not functioning correctly, the regulator will make a vehicle run hot, blow smoke, experience poor mileage and use excessive amounts of oil. Fuel pressure regulators are responsible for prescribing the correct amount of fuel the injection system directs to the pistons. This must be accomplished with consistent application and pressure for a vehicle to function properly.
Things You’ll Need
Fuel pressure gauge
Testing a Fuel Pressure Regulator
1. Locate and remove the cap on your vehicle’s fuel pressure regulator. If you are uncertain about the regulator’s location consult your owner’s manual, but in general, find it by checking along your fuel rail. Fuel rails enter on the side of the vehicle where the fuel tank is located and are connected to all parts of the engine that need fuel. Fuel pressure regulators are the last thing in the engine to receive fuel before the rail exits the engine compartment.
2. Rotate the key in the ignition to the on position without starting the vehicle. Attach the fuel pressure gauge to the threaded spot that appeared when you removed the regulator’s cap. Record the reading on your fuel pressure gauge and compare it with the proper pressure for your vehicle. Consult your manual for proper readings.
3. Turn the engine on and recheck the reading on the gauge. Locate the throttle and engage it. The reading on the gauge will rise about 5 psi unless your regulator is malfunctioning or your fuel filter is clogged. In this case you will see no change or a drop in psi.
Testing a Regulator’s Diaphragm
1. Locate the vacuum hose attached to your regulator.
2. Remove the vacuum line from the fuel pressure regulator and inspect it to see if fuel is present.
3. Replace the diaphragm if you observe fuel in it, as this is an indication that the present diaphragm has ruptured allowing fuel into the line. This fuel travels to your vehicle’s intake system causing poor performance and thick black smoke.






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