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Check Fuel Pump and Regulator Test

Check Fuel Pressure Video

Your car's engine depends on constant fuel under pressure to supply the fuel injection system properly. Your car's fuel pump performs this action and is located in or near the gas tank. The injection system meters fuel through the fuel injectors and into the engine. Many engine run ability problems can be related to a weak or failing fuel pump. Problems can range from hard starting in the morning, low power and stalling while driving. Most vehicles have a fuel pressure test port somewhere on the fuel rail, use a flash light to locate it on your engine or consult a car repair manual.

With the engine off remove the protective cap and attach the fuel pressure gauge. Support the gauge for observation; now turn the key to the on position. The fuel pressure gauge should jump up to your system pressure, in most cases 45 p.s.i. to 55 p.s.i. is standard in port injection system and 14 p.s.i. to 18 p.s.i. in TBI (throttle body injection) systems. When testing fuel pressure may vary slightly but should be pretty close to spec. To find exact pressure for your vehicle consult a car repair manual. (Note: Some cars do not have a test port; in this case you must use a fuel filter bypass hose to "tee" the fuel pressure gauge in for testing)

Most vehicles utilize a fuel injection system to deliver fuel to the engine. Correct fuel system pressure is essential for proper engine operation, in fact many engine run-ability problems can be related to weak fuel system pressure. A fuel injection system contains a fuel pump to supply fuel from the tank into the fuel system. The fuel filter cleans fuel before fuel enters the fuel injectors. The fuel pressure regulator adjusts fuel system pressure depending on the load of the engine.

Typical Fuel Injection System

Vacuum that is attached to the fuel pressure regulator to control system pressure. When the fuel pressure regulator is not functioning properly it causes the fuel pressure to be above normal operating pressure. This condition causes excess fuel to be injected into the engine causing a rich mixture that produces black smoke. To test fuel system pressure and fuel pressure regulator operation (engine off) remove the protective cap and attach the fuel pressure gauge.

Connect Fuel Pressure Gauge

Support the fuel pressure gauge for observation, then turn the key to the on position. The fuel pressure gauge should jump up to your system pressure. If you do not know your vehicle system fuel pressure consult a repair manual. Actual fuel system pressure will very slightly but should pretty close to specification.

Then, start the engine the fuel system pressure should stay the same. While watching the gauge snap the throttle, the fuel system pressure should jump up about 5 psi. If the system fuel pressure does not respond the fuel pressure regulator has failed. If the fuel pressure gauge falls the fuel filter is plugged or the fuel pump is failing. When testing is complete, remove the fuel pressure gauge feed line and replace the protective dust cap.

Testing for a Blown Fuel Pressure Regulator Diaphragm. A fuel pressure regulator is used in the fuel injection system. This component regulates fuel system pressure by using a diaphragm and spring combination. When the fuel pressure regulator diaphragm ruptures it allows raw fuel into the vacuum feed line and then into the intake system of the engine. This condition creates a rich black smoke from the tail pipe on start up and while running.

Removing the Vacuum Feed Line from Fuel Pressure Regulator

To check for this condition remove the vacuum line from the regulator, if fuel is present in the line the regulator has failed. Some GM vehicles are designed with an internal intake regulator you must remove the upper intake manifold to be inspected. Most fuel pressure regulators are on the fuel rail on top of the engine in plain site. If you can not locate your fuel pressure regulator consult a repair manual.

Fuel Pump Pressure and Pressure Regulator Test

Tools needed to perform these tests: Fuel Pressure Gauge

Step 1 - Check pump performance, while observing the gauge rap the throttle, the gauge should move up about 5 p.s.i. if the gauge moves down you have a bad fuel pump or a plugged fuel filter, remove the filter for inspection, if it's ok, replace the fuel pump with new and re-test system.

Step 2 - Check the fuel pump and pressure regulator while the engine is running. Start the engine and allow it to idle, while observing the gauge remove the vacuum line, the gauge needle should move up about 5 to 10 p.s.i., if the gauge stays the same when the vacuum line has been removed the regulator is bad and needs replacement.

Common Problems:

If too much amperage is being drawn through the fuel relay circuit it can cause the relay contacts to "stick" not allowing the power to be shut off to the pump and draining the battery down.
A fuel pump can fail while driving for this you need to monitor the gauge while driving. You can do this by attaching a small extension hose and temporally attaching the gauge so it can be seen from the driver's compartment. If the gauge drops at anytime the fuel pump system is failing. Anytime you replace the fuel pump you should replace the fuel pump relay. The relay supplies power to the pump and can be easily overworked by a failing pump.

If further assistance is needed, our certified car repair technicians are ready to answer your car questions.

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