1989 Mercedes Benz 300CEFACTORY OEM SERVICE PROCEDURE

System Pressure

  1. There are 2 versions of Fuel Pressure Gauge (100 589 00 21 00) available. One version has junction block with 2 valve handles which are numbered "1" or "3" in the following procedure. The hose exiting from the side of junction block by No. "1" valve handle is hose "1".
  2. The second version of Fuel Pressure Gauge (100 589 00 21 00) has single a valve handle on junction block. Hose leaving junction block 180 degrees from valve handle is hose "B" and hose leaving junction block 180 degrees from line to gauge is hose "A". When testing system pressure using first version of fuel pressure gauge, close valve "1" and open valve "3". On second version, open valve.
  3. Remove plug from test port in lower chamber of fuel distributor. Connect fuel pressure gauge line "1" or "A" to test port in lower chamber of fuel distributor. Use M12 X 1.5/M8 X 1 Reducing Bushing (102 589 06 63 00) to facilitate connecting hose to chamber port.
  4. Remove fuel supply line for cold start valve from top of fuel distributor. Attach pressure gauge line "3" or "B" to cold start fitting on fuel distributor upper chamber. System pressure is checked with engine off. Engine temperature has no effect upon system pressure test. Remove fuel pump relay. Bridge terminals No. 7 and 8.
  5. System pressure should be 76.9-79.8 psi (5.4-5.6 kg/cm2 ). If not, check for defective fuel pump, restricted fuel return line or defective differential pressure regulator. Open pressure gauge valve "1". Remove fuel pump relay bridge.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.