How do you tll if you fuel ump is going out in a 2001 mercury marquis?

Answer 1

Buy a fuel pressure gauge at your local auto parts store and check the fuel pressure. Purchase the model with a small plastic bleed down tube and a bleed down button.

There is a fitting on the fuel rail that resembles a tire valve. Remove the cap and (CAUTION) carefully attach the fuel gauge. The fuel in the rail will probably be under pressure and a small amount will leak out when you attach the gauge. It is best to attach the gauge when the engine is cold and in an open space. Make certain there are no open flames or other sources of ignition nearby.

1. After the gauge is attached turn the ignition switch to the on position. The fuel pressure should immediately come to 30-40 pounds per square inch and hold steady. If the pressure does not rise the pump is defective, the fuel filter or line is completely plugged or the pressure regulator is defective. If the pressure rises and holds steady go to step 2.

2. Start the engine and the pressure gauge should drop to a lower level and hold steady with a slight pulsation of the pressure gauge indicator needle. Next, slightly accelerate the engine with the gas pedal. The pressure should immediately increase and then drop back to normal run position each time you tap the gas pedal. If this occurs as described the pressure regulator is functioning properly. The pressure regulator is a pancake shaped device on the return side of the fuel rail with a vacuum hose attached to it. When the engine is accelerated, engine vacuum temporiarily decreases and the pressure regulator momentarily raises fuel pressure. If this does not occur the engine will stumble each time you accelerate it. The pressure regulator momentarily raises fuel pressure when the engine is accelerated so that more fuel is delivered to the fuel injectors. This duplicates the function of the accelerator pump in carburetors on older non fuel injected engines.

3. To check for adequate fuel delivery at driving speeds you will need to check fuel flow at higher levels. Obtain a small fuel container and place the end of the small plastic fuel bypass line inside the container. (CAUTION) Make sure no open flames or other sources of ignition are nearby and start the engine. Depress the bypass button on the fuel gauge and fuel should start flowing down the bypass tube and fuel pressure should drop to approximately 5 pounds per square inch. The engine will run with 5 pounds of fuel pressure but may not be smooth. Releasing the bypass button should immediately raise the fuel pressure back to the normal run level. If the fuel pressure drops lower than 5 pounds or the engine stalls the pump is not delivering adequate fuel. The pump is defective or the fuel line is blocked. Replace the fuel filter first and if this does not solve the problem the fuel pump will need to be replaced. The fuel tank will need to be removed to replace the pump and this is best left to a professional repair service unless you have the equipment and experience to do this.