To check the pressure in the fuel supply system, a pressure gauge and an appropriate adapter are required to connect to the system.
Reduce the pressure in the fuel supply system. Reconnect the fuel pump connector or connect the wire to the pump relay.
Remove the hose connecting the fuel filter to the fuel distribution line, and install a pressure gauge in the gap by screwing it onto the tee.
Start the engine and warm it up to operating temperature. Check fuel pressure.
If there is no fuel pressure (even with the fuel pump running), the fuel filter connected in series to the line may be clogged. Replace filter and check pressure again. If there is still no pressure, the cause may be a clogged fuel line. If the line is not clogged, check the fuel pump inlet filter. Check the electrical resistance of the pump.
If the fuel pressure is low, the cause may be a partially clogged fuel pump inlet filter. Replace filter and check pressure again. If the pressure is still low, check the tightness of the connection of the pipeline and the entire line. Check the pressure regulator, fuel rail and injectors for leaks. If no leaks are found, pinch the fuel return line (hose at the connection with the pressure regulator) and with a jumper, connect the diagnostic contacts of the connector on the bulkhead of the engine compartment (fig.15.16). Take note of the pressure reading. If the pressure is above the lower limit, then the fuel pressure regulator is faulty. If the pressure is still low after replacement, replace the fuel pump.
If the fuel pressure is high, disconnect the flexible fuel return hose and put a rubber hose with an inner diameter of about 8 mm on the free fitting on the side of the pressure regulator. Place the other end of the hose into a container of fuel. Use a jumper to connect the diagnostic contacts of the connector on the bulkhead of the engine compartment and note the pressure reading. If the pressure is still above the low limit, replace the pressure regulator. If the pressure is correct after replacement, the fuel return line is clogged.