LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Mercedes Benz >> 1990 >> 560SEL >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - System/Component Tests >> Fuel System >> Lower Chamber (Differential) Pressure Test
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Lower Chamber (Differential) Pressure Test

  1. Connect Meter Adapter Cable (102 589 04 63 00) between differential pressure regulator and ammeter. Disconnect O2 sensor lead at connector located under right front floor mat. Turn ignition on. Meter reading for lower chamber pressure should be constant 7-9 mA. If reading is incorrect, check lambda control.
    NOTE: During warm-up and at operating temperature, current to differential pressure regulator is determined by coolant temperature sensor, O2 sensor and ECU.
  2. Bridge fuel pump relay socket, terminals Nos. 7 and 8 with jumper wire. Lower chamber pressure should be about 5.8 psi (.4 kg/cm2 ) less than system pressure reading determined earlier. Unplug coolant temperature sensor.
  3. Note lower chamber pressure and differential pressure regulator current. If coolant temperature sensor plug is disconnected, temperature sensor resistance should be zero ohms, differential pressure regulator current should be about 114-132 mA, and lower chamber pressure should be about 15.95-18.85 psi (1.1-1.3 kg/cm2 ) less than system pressure. Reconnect coolant temperature sensor.
  4. Check pressure and current values at coolant temperature of 68°F (20°C). Sensor resistance should be 2200-2800 ohms. Differential pressure regulator current 9-14 mA and lower chamber pressure should be about 5.8 psi (.4 kg/cm2 ) less than system pressure.
  5. Check pressure and current values at coolant temperature of 176°F (80°C). Sensor resistance should be 290-370 ohms, differential pressure regulator current 7-9 mA and lower chamber pressure should be about 5.8 psi (.4 kg/cm2 ) less than system pressure.
  6. Check pressure and current values at coolant temperature of 212°F (100°C). Sensor resistance should be 140-220 ohms, differential pressure regulator current 7-9 mA and lower chamber pressure should be about 5.8 psi (.4 kg/cm2 ) less than system pressure.
  7. If not to specification, check coolant temperature sensor for malfunction. Coolant temperature sensor should also be checked if there are warm-up problems with vehicle. Test lambda control. If lower chamber pressure is too high, check orifice in fuel distributor for restriction. Install fuel pump relay. Reconnect O2 sensor.
scientia non olet · About LEMON Manuals