Automobile fuel injections systems are designed to operate at a specific internal fuel pressure, controlled by the fuel pressure regulator. Fuel injection systems are sensitive enough so even the slightest variation in fuel pressure can cause a malfunction in the fuel system. The most common cause of fuel pressure irregularities is damage to the diaphragm in the fuel pressure regulator, allowing fuel to back up into the vacuum system. You can check this with a fuel pressure gauge.
Locate the fuel system test port on the fuel system rail. The rail resembles a tube running between the fuel pump and the throttle body (or carburetor) and has what looks like a tire air valve stem with cap. Be certain you do not mistake the AC access tube for the fuel system rail. If in doubt, trace the line in both directions to be sure it is not connected to the air conditioning compressor.
Unscrew the cap from the fuel system test port with your fingers. If the cap sticks twist it gently with the pliers.
Screw the hose fitting of the fuel pressure gauge onto the test port. Set the gauge where it will not be vulnerable to moving parts of the engine, and start the vehicle.
Read the fuel pressure gauge, and then remove the rubber vacuum line attached to the throttle body (or carburetor) assembly. If the reading on the gauge does not increase at least 5 psi after the vacuum line is removed, the fuel pressure regulator is faulty.
