Workshop Hints

Workshop Hints
Before any service work is performed on any ignition system related component, always adhere to the following:
^ Observe relevant safety legislation pertaining to your area
^ Always wear adequate protection clothing including eye protection
^ Use caution when working around a HOT engine compartment
^ Always consult the REPAIR INSTRUCTIONS on the specific model you are working on before attempting a repair.
^ Always SWITCH OFF THE IGNITION (ILL 15) before working on the ignition system.
^ Use only BMW approved test leads.
^ NEVER TOUCH COMPONENTS CONDUCTING CURRENT with the engine running.
^ Do not connect suppression devices or a test light to terminal 1 of the ignition coils.
^ Terminal 1 from the ignition coil to the ECM (High Voltage approximately 350 V)

HIGH VOLTAGE - DANGER!

Caution: Hazardous voltages occur at:
^ Ignition Leads
^ Spark Plug Connector
^ Spark Plug
^ Ignition Coil (High Voltage at terminal 4 is approximately 40 KV)
^ Terminal 1 from the ignition coil to the ECM (High Voltage approximately 350V)

Ignition System Diagnosis





A fault survey should first be performed using the DlSplus/GT1 to determine if there is a fault in the primary ignition or secondary ignition. If there is a fault in the primary ignition, testing should include:
^ Power Supply at the coil (KL 15)
^ Resistance of the harness and ignition coil primary winding
-using the Universal Adapter with the ECM disconnected





ECM Final Stage transistor activation. This test function is found under the Oscilloscope Preset list Ignition Signal Primary (normal Terminal 1 Signal shown on the right).
Install the Universal Adapter, Diagnostic cable, MFK 2 negative lead to ECM ground and MFK 2 positive lead to the ground activation circuit for Terminal 1 of the ignition coil. This test is performed with the engine cranking/running.
If there is a fault in the secondary ignition, testing should include:
^ Primary Ignition
^ Evaluation of Secondary Oscilloscope Patterns





The Following are Examples of Secondary Oscilloscope Patterns (consult Repair Instructions for ignition pattern variations per coil manufacturer):
This is a normal pattern for one ignition circuit with the engine at idle speed.
^ Normal Combustion Period
^ Normal Ignition Voltage Peak





Multiple Ignition Pulses ensure good spark quality during engine start up. The ECM will activate the ignition coils 9 times per 720° of crankshaft revolution.
This is a normal pattern for one ignition circuit when:
1. Normal Combustion Period
2. Normal Ignition Voltage Peak
Long Spark Period (1) with Low Ignition Voltage Peak (2). If Spark Period is Fluctuating:
^ Indicates Low Compression
^ Contamination on Spark Plug or Defective Spark Plug





Short Spark Period (1) with High Ignition Voltage Peak (2).
^ Defective Ignition Connector or Resistive Adaptive Boot





Evaluation of Ignition Voltage Peaks at Idle Speed (Multiple Cylinders Displayed).
1. Normal Attenuation (Voltage Reduction) Process
2. Shorten Attenuation Process (arrow) Defective Ignition Coil
3. Absence of Attenuation (arrow) Defective Ignition Coil





No Sparking Voltage Line (Single Cylinder Displayed)
^ Defective Ignition Coil





Evaluation of Ignition Voltage Peaks under Sudden Loads (Multiple Cylinders Displayed).
^ Defective Ignition Coil
Decaying Process is considerably Higher than Ignition Voltage Peak (2):
^ Lean Mixture
^ Defective Fuel Injector
^ Low Compression

The Repair Instructions should be consulted for additional Oscilloscope Patterns under various engine speeds.
In Summary,
If the Secondary Ignition Voltage is Too High (Excessive Resistance for Ignition):
^ Spark Plug Gap is to Large (Worn or Burned)
^ Incorrect Heat Range Spark Plug
^ Compression is too High (Carbon, etc.)
^ Interruption in the Secondary Ignition Connector or Resistive Adapter Boot

If the Secondary Ignition Voltage is Too Low (Low Resistance for Ignition):
^ Spark Plug Gap is Too Small (Mishandled on Installation)
^ Incorrect Heat Range Spark Plug
^ Compression is Too Low
^ Voltage Leak in the Secondary Ignition Connector or Resistive Boot to Ground

Spark Plugs





The Spark Plugs should be inspected for the proper type, gap and replaced at the specified intervals.


Knock Sensors





The Knock Sensors should be tested using the DIS/GT1 for:
^ Fault Codes
^ Status Display Knock Control (active / not active)
^ Oscilloscope Display (Low DC Voltage mV setting)

When installing Knock Sensors:





DO NOT MIX THE LOCATIONS or Engine Damage will result! The Knock Sensors use a combined connection to the engine harness. The Knock Sensor with the shorter cable is for cylinders 4 - 6.
Do Not Over Tighten attaching bolt! Piezo ceramic will be cracked. Torque to 20 Nm.
Do Not Under Tighten attaching bolt, a lose sensor can vibrate producing a similar signal to a knock.