Mercedes Coupes/Sedans/Wagons 1974-1984 Repair Guide

Distributor

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REMOVAL & INSTALLATION



The removal and installation procedures for all distributors on Mercedes-Benz vehicles are basically similar. However, certain minor differences may exist from model to model.

  1. The distributor (on most models) is located on the front of the engine.
  2.  
  3. Remove the dust cover, distributor cap, cable plug connections and vacuum line.
  4.  
  5. Rotating the engine in the direction of normal rotation, crank it around until the markings on the distributor rotor and distributor housing are aligned.
  6.  
  7. The engine can be cranked with a socket wrench on the balancer bolt or with a small prybar inserted in the balancer.
  8.  
  9. Matchmark the distributor body and the engine so that the distributor can be returned to its original position. White paint can be used for this purpose. The notch on the rim of the distributor housing indicates No. 1 cylinder.
  10.  
  11. Remove the distributor hold-down bolt and withdraw the distributor from the engine.
  12.  

Do not crank the engine while the distributor is removed.

  1. To install the distributor, reverse the removal instructions. Insert the distributor so that the matchmarks on the distributor and engine are aligned.
  2.  
  3. Tighten the clamp bolt and check the dwell angle and ignition timing.
  4.  

TESTING



The following testing procedures apply only to electronic ignition distributors.

Except 1981 6-Cyl. and 1984 4-Cyl. Engines See Figures 1 and 2

Click image to see an enlarged view

Fig. Fig. 1: Use an ohmmeter to check armature resistancepre-1980 electronic ignition



Click image to see an enlarged view

Fig. Fig. 2: Use an ohmmeter to check pick-up coil resistancepre-1980 electronic ignition

  1. Check the screw type plug terminals and the plug wires.
  2.  
  3. With the ignition ON, a primary current of about 8 amps will flow continuously through the system.
  4.  
  5. Check the input voltage at the terminal block. Terminal 15 should show 4.5 volts and terminal 1 should show 0.5-2.0 volts. If the voltage at terminal 1 is excessive, replace the switching unit.
  6.  
  7. If there is no spark but terminal 1 voltage is OK, check the armature resistance (terminal 7 and 31d). Resistance should be 450-750 ohms.
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  9. Test the pick-up coil resistance. There should be infinite resistance between terminal 7 and ground.
  10.  
  11. Check the armature and pick-up coil for mechanical damage. An air gap should exist between them.
  12.  
  13. Check the dwell angle. Even though it cannot be adjusted, it should be 25-39- at 1,400-1,500 rpm.
  14.  
  15. If the armature and pick up coil are functioning, replace the switching unit. If the armature and pick-up coil indicate no damage, replace the switching unit. If the armature or pick-up coil are defective, replace the distributor.
  16.  

1981 6-Cylinder Engines

This engine uses a new breakerless transistorized ignition system with no preresistance and no current flow unless the engine is running. The new system consists of ignition coil, distributor, harness and switching unit. Do not replace the coil with a previously used coil. Also, see the ignition system precautions given previously.

  1. Test the voltage between bushing 5 of the diagnosis plug and ground with the ignition ON. Nominal battery voltage should be indicated. If not, test the voltage via the ignition switch. If voltage is correct, go to Step 2.
  2.  
  3. Test the voltage between bushing 4 and 5 of the diagnosis plug socket. Zero voltage should be indicated. If voltage is more than 0.1 volt, switch off the ignition immediately. Renew the switching unit. Check the pressure relief plug in the ignition coil and the ohmic value of the ignition coil between terminals 1 and 15. If the pressure relief plug has popped out or the resistance is not .7\#189>, replace the ignition coil.
  4.  
  5. Test the dwell angle. It should be 7-25-. If more than 25-, replace the switching unit. If no reading or the reading is correct, go to Step 4.
  6.  
  7. Disconnect the green control line from the switching unit and test the resistance between terminals 3 and 7. Resistance should be 500-700ohms. If the resistance is wrong, pull the green cable from the distributor and see if there are 500-700 ohms present at the connector plugs. If so, replace the green cable. If not, replace the distributor.
  8.  
  9. Remove the green cable from the control unit. There should be 200 k\#189> between terminals 3 or 7 and ground. If not, disconnect the green cable from the distributor and test the resistance between any of the plugs and ground. If 200 k\#189> are not present, replace the distributor.
  10.  

1984 4-Cylinder Engines

The electronic ignition system on the 190E differs from the previous systems with the addition of a small switching unit.

The base plate on this switching unit serves as a heat sink; periodic cleaning will ensure proper heat flow between it and the wheel arch.

The ignition coil and all testing procedures are similar to those given for the 1981 6-cylinder engine.

 
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