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 the 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 the filter and check the pressure again. If there is still no pressure, the cause may be a clogged fuel line. If the line is not clogged, check the filter at the fuel pump inlet. Check the electrical resistance of the pump.
If the fuel pressure is low, the cause may be a partially clogged filter at the fuel pump inlet. Replace the filter and check the pressure again. If the pressure is still low, check the tightness of the pipe connection and the entire line. Check the tightness of the pressure regulator, fuel distribution line and injectors. If no leak is detected, pinch the fuel return line (hose at the connection point with the pressure regulator) and use a jumper to connect the diagnostic contacts of the connector on the engine compartment bulkhead (figure 15.16). Remember the pressure reading. If the pressure is above the lower limit, the fuel pressure regulator is faulty. If the pressure is still low after replacement, replace the fuel pump.
(Article is based on website data: mazbook.ru)
If the fuel pressure is high, disconnect the flexible fuel return hose and attach a rubber hose with an internal diameter of approximately 8 mm to the freed fitting on the pressure regulator side. Place the other end of the hose in a container containing fuel. Use a jumper to connect the diagnostic contacts of the connector on the engine compartment bulkhead and remember the pressure reading. If the pressure is still above the lower limit, replace the pressure regulator. If after replacement the pressure is normal, then the fuel return line is clogged.