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BMW

Ignition Coil Failure - 1991 BMW 525i with M50 Engine

 

Situation: A complaint of rough idle and/or a misfire under heavy engine load may be received on E36 and E34 (M50 equipped) vehicles due to a break on the secondary side of the ignition coils.  These coils were produced by the vendor named "May und Christ".

 
Correction: If a vehicle is encountered with the above complaint, proceed as follows:

With the cylinder head cover removed (exposing the tops of the ignition coils) identify the vendor:

Vendor                                  Identification

"May und Christ"                 = ZUNDSPULE
Bosch                                    = Bosch

Identify the production year and month of the "May und Christ" coils located directly above the word ZUNDSPULE, i.e., 91 M 06 (year = 91, month = 06 (June) ).  Coils with a production date code prior to 91 M 01 (January 1991) may have a break on the secondary side which can be diagnosed removing the ignition coil from the engine.  With the coil removed, twist and pull the spark plug connector off the coil and examine the connection.

A poor connection may be seen as green corrosion or (a) piece(s) of plastic found in the ignition coil socket, which as broken off the spark plug connector.  In this case, the coil must be replaced.

 
Note: A further check can be performed when diagnosing the primary and secondary signals of an ignition coil as outlined in E36 Repair Manual microfiche, Group 12, Page 12-13/3, using the BMW Service Tester and special tool adapter cables.  However, the secondary signal scope pattern may be misleading and may not diagnose a coil which is defective under engine load, i.e., a large spike displayed on the scope screen.

 
Parts Information Replace the coils with BWC #178-8154

 
Source: Alldata, Bulletin #12 02 92 (3506)

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