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Home >> Land Rover >> 1994 >> Defender 90 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Basic Diagnostic Procedures - 3.5L, 3.9L & 4.2L >> Fuel Systems >> Depressurizing/Pressurizing Fuel System
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Depressurizing/Pressurizing Fuel System

  1. Remove fuel pump relay module. Start and run engine.
  2. NOTE: Fuel at low pressure will remain in system. To remove low pressure fuel, place absorbent cloth around fuel pipe at the filter during disconnection.
  3. When sufficient fuel has been used to cause fuel line pressure to drop, injectors will become inoperative, resulting in engine stall. Switch off ignition. Disconnect the battery negative lead.
  4. Connect the pressure gauge on the outlet from the filter, located on the chassis under the right rear wheel arch. See Fig 1 .
  5. Reconnect the battery and turn the ignition to ON position, while observing pressure gauge. Pressure should be 2.39-2.67 kgf/cm2 . Maximum allowable pressure drop is 0.7 kgf/cm2 per minute. If pressure is low, ensure filter is not blocked and pump is operating correctly, recheck pressure. If pressure is still low renew regulator. Repair or replace fuel pressure regulator as necessary. After completing the tests, retest the vehicle to ensure the faults have been rectified. If faults still persist, recheck using Lucas diagnostic equipment.
    Fig 1: Identifying Fuel Flow
    G00079868Courtesy of LAND ROVER NORTH AMERICA, INC.