System pressure is the pressure created by the fuel pump and regulated by the diaphragm pressure regulator shown in Fig. 6-51. Above the predetermined pressure limit of the regulator, the regulator opens and returns excess fuel to the fuel reservoir. System pressure is not adjustable. A faulty pressure regulator should be replaced as described in 4.4 Fuel Pressure Regulator.
To check system pressure, connect the fuel pressure gauge as described above and disconnect the harness connector from the differential pressure regulator. Bypass the fuel pump relay to run the fuel pump and pressurize the fuel system, as described in 4.1 Fuses and Relays. Read system pressure with the gauge valve open, then disconnect the relay bypass to shut off the fuel pumps. The correct system pressure values are listed in Table k.
Table k. System Pressure Specifications
(CIS-E and CIS-E Motronic)
If system pressure is too high, check for a blocked or damaged fuel return line. If system pressure is too low, look for fuel leaks, a clogged fuel filter, or a damaged fuel line blocking fuel flow. Check fuel pump delivery rate as described in 4.3 Fuel Pump. If no faults are found with the fuel lines or the fuel pumps, the pressure regulator is faulty and should be replaced.
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