1985 Mercedes Benz 300CDFACTORY OEM SERVICE PROCEDURE

Injection Nozzles

  1. At idle, loosen each injection pipe cap nut (in turn) one-half turn. If sound of engine does not change, part of problem is a defective nozzle or inadequate sealing between pipe union and nozzle holder.
  2. Raise engine RPM above idle speed and repeat test procedure. If engine still does not run erratically with nut loosened, repair or replace that particular nozzle. If engine runs erratically when nut is loosened, nozzle is operating properly. Tighten one-half turn and check next nozzle.
  3. Remove each injection nozzle and check opening pressure using injection nozzle tester. Spray patterns should be even and fine. If nozzle spurts or sprays drops, replace it.
  4. After determining opening pressures, pump pressure up slowly until it is 280 psi (19.7 kg/cm2 ) BELOW opening pressure. Nozzle should not leak or drip for 10 seconds.
    NOTE: Nozzle opening pressure can be adjusted by changing shims. Increasing shim thickness by .002" (.05 mm) will increase injection pressure by about 45 psi (3 kg/cm2 ). Shims are available in thicknesses from .039-.070" (1.0-1.8 kg/cm2 ) in increments of .002" (.05 mm).
  5. When replacing nozzles, always install new seal between nozzle and prechamber. Tighten nozzles carefully to specified torque.
INJECTION NOZZLE OPENING PRESSURES

Application psi (kg/cm2 )
New 1960-2075 (135-143)
Used 1740 (120)
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Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
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  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
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