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Home >> Mazda >> 1988 >> 929 Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Fuel Injection System - BOSCH AFC >> Testing >> Fuel Pressure
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Fuel Pressure

CAUTION: Constant fuel pressure is maintained in fuel lines and component parts at all times. Relieve pressure before attempting to open system for testing. Do not allow fuel to flow onto engine or electrical parts or allow an open flame in area while testing fuel system components.
  1. Relieve fuel system pressure. Disconnect negative battery cable. Disconnect fuel filter hose from high pressure side. Connect Multi-Pressure Tester (49-9200-750A) between fuel hose and pulsation damper.
  2. Disconnect vacuum line from pressure regulator control solenoid valve. Using a "T" connector, connect tester vacuum hose to solenoid valve. Connect negative battery cable. Connect tester to vehicle battery.
  3. Connect a jumper wire across Yellow test connector terminals located near airflow sensor on 929 and near windshield wiper motor on all other models. Turn ignition on. Check connections for leaks. Turn ignition off. Disconnect jumper wire from Yellow test connector.
  4. Start engine and warm to operating temperature. Position lever on adapter (in fuel line) so handle is parallel with fuel line. Operate engine at various speeds. On 323, 626 and MX-6, fuel pressure should be 34-40 psi (2.4-2.8 kg/cm2 ) and on 929, pressure should be 38-45 psi (2.7-3.2 kg/cm2 ). If fuel pressure is not to specification, check fuel pump, fuel lines and injectors.
  5. Turn ignition off. Connect a jumper wire across Yellow test connector terminals. Turn ignition on. Position lever on adapter (in fuel line) so handle is perpendicular to fuel line. Fuel pressure should be 64-85 psi (4.5-6.0 kg/cm2 ). If fuel pressure is not to specification, check fuel pump volume. If fuel pressure is more than specified, replace fuel pump.
  6. Disconnect jumper wire from Yellow test connector. Start engine. Position lever on adapter so handle is parallel to fuel line. With engine idling, fuel pressure should be 24-31 psi (1.7-2.2 kg/cm2 ) on 323, 27-33 psi (1.9-2.3 kg/cm2 ) on 626 and MX-6, 31-38 psi (2.2-2.7 kg/cm2 ) on 929. If fuel pressure is not within specification, check pressure regulator and pressure regulator control solenoid valve vacuum hose.
  7. Disconnect fuel pressure regulator vacuum hose. Fuel pressure should be 34-40 psi (2.4-2.8 kg/cm2 ) on 323, 626 and MX-6 models and 38-45 psi (2.7-3.2 kg/cm2 ) on 929. If fuel pressure is within specification, replace fuel pressure regulator.
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