Mercedes Coupes/Sedans/Wagons 1974-1984 Repair Guide

Fuel Filter

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REMOVAL & INSTALLATION



Gasoline Engines
4-CYLINDER CARBURETED ENGINE
  1. Loosen the hose clips.
  2.  
  3. Remove the fuel filter.
  4.  
  5. Install a new filter in the direction of flow (arrow) along with new fuel hoses.
  6.  
  7. Replace the hose clips.
  8.  
  9. Check for proper sealing.
  10.  

6-CYLINDER CARBURETED ENGINES

The fuel filter is located in the carburetor housing. Put some rags under the fuel return valve to absorb the inevitable gasoline spillage.

  1. Unscrew the fuel return valve and plug it at the carburetor.
  2.  
  3. Remove the fuel filter.
  4.  
  5. Renew the gasket at the seal plug.
  6.  
  7. Install a new filter. Check for leaks.
  8.  

FUEL INJECTED ENGINESALL MODELS

Two types of filter are used, one on the electronically controlled fuel injection and the other on the CIS fuel injection. Both are located between the rear axle and the fuel tank.

  1. Unscrew the cover box.
  2.  
  3. Remove the pressure hoses.
  4.  
  5. Loosen the attaching screws and remove the filter. Remove the connecting plug from the old filter and install it on a new filter using a new gasket.
  6.  
  7. Install a new filter in the direction of flow.
  8.  
  9. Replace the attaching screws.
  10.  
  11. Install the pressure hoses.
  12.  
  13. On 1976 and later models, install the fuel filter in the holder by positioning it in the center of the transparent holder.
  14.  
  15. Replace the cover box and check for proper sealing.
  16.  

Diesel Engines

MAIN FUEL FILTER-1974-76 240D AND 300D MODELS

See Figures 1 through 6

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Fig. Fig. 1: View of the diesel engine fuel filter1974-76 models. Later models use an upright filter



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Fig. Fig. 2: To remove the fuel filter, loosen the filter's center bolt ...



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Fig. Fig. 3: ... then support the fuel filter and unscrew the center bolt



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Fig. Fig. 4: 1. Center Bolt 2. Fuel Filter Remove the filter and the center bolt



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Fig. Fig. 5: To bleed the injection pump on 5-cyl. engines, open the bleed screw atop the filter housing ...



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Fig. Fig. 6: ... then operate the hand pump until the fuel emerges free of air bubbles

  1. Drain the fuel from the housing.
  2.  
  3. Remove the center bolt and remove the filter housing and filter.
  4.  
  5. Wash the filter housing in clean diesel fuel and install a new filter element.
  6.  
  7. Use a new gasket in the filter cap and reassemble the filter and housing.
  8.  
  9. Bleed the injection pump. On 5-cylinder engines, loosen the bleed bolt on the fuel filter housing and release the manually operated delivery pump. Operate the delivery pump until the fuel emerges free of bubbles at the bleed screw. Close the bleed bolt and operate the pump until the overflow valve on the injection pump opens (a buzzing noise will be heard). Close the manual pump before starting the engine. To bleed the injection pump on 4-cylinder diesels, loosen the bleed screw on the injection pump and keep pumping the hand pump until fuel emerges free of bubbles.
  10.  

The 190D uses a self-bleeding fuel pump, therefore the hand pump has been eliminated. No bleeding is necessary.

MAIN FUEL FILTER 1977-84 MODELS

Loosen the center attaching bolt and remove the filter cartridge downward. Lubricate the new filter gasket with clean diesel fuel and install a new filter cartridge.

To bleed the fuel filter, see Step 5 of the previous procedure.

DIESEL PREFILTER

Diesel engines use a prefilter in addition to the main fuel filter, since even the most minute particle of dirt will clog the injection system. The prefilter is located in the line just before it enters the injection pump.

Unscrew the clamps on each end and remove the old filter. Install a new filter and bleed the system (see Main Fuel Filter).

 
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