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Home >> Mercedes Benz >> 1985 >> 300CD >> Repair and Diagnosis >> Engine Performance >> System >> Fuel Injection System - Diesel >> Testing >> Fuel Pump >> Delivery Pressure Check
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Delivery Pressure Check

  1. Install pressure tester between main fuel filter and injection pump (Bosch Part No. 000 589 49 21 00). Check for air bubbles in fuel and bleed filter and tester until no bubbles are present.
  2. With engine idling, pressure should be 8.5-11.4 psi (0.6-0.8 kg/cm2 ). With engine at 3000 RPM, pressure should be 11.4 psi (0.8 kg/cm2 ). If not, check by-pass valve in pump or for damaged fuel lines.
  3. During pressure checks, watch for bubbles in sight glass tube on tester. If bubbles appear, check system carefully for leaks. Repair or replace fittings, hoses and clamps as necessary.
  4. Check delivery end (final) pressure. Clamp fuel return hose closed and see how high pressure builds. At idle, pressure should be at least 15.6 psi (1.1 kg/cm2 ); at 3000 RPM pressure should be at least 18.5 psi (1.3 kg/cm2 ).
  5. If pressures are not correct, clean or replace by-pass valve of fuel pump.
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