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 protective 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 (KL15) 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 of the ignition coil must not be connected to Ground or B+.
- Never run the engine with a secondary ignition component disconnected.

HIGH VOLTAGE - DANGER!


CAUTION! Hazardous voltages occur at:
- Ignition Leads
- Spark Plug Connector
- Spark Plug
- Ignition Coil (High Voltage at terminal 4 is approximately 30 KV)
- Terminal 1 from the ignition coil to the ECM (High Voltage approximately 350 V)


Ignition System Diagnosis
A fault survey should first be performed 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 (KL15)
- Resistance of the harness and ignition coil primary winding (terminal 15 to 1 approx. 0.8 ohms) - using the 134 Pin Adapter Set with the ECM disconnected.







- ECM Final Stage transistor activation. This test function is found under the Oscilloscope Preset list - "Ignition Signal Primary".







Install the 134 Pin Adapter Set, 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 running.

If there is a fault in the secondary ignition, testing should include:
- Primary Ignition
- Evaluation of Secondary Oscilloscope Patterns

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.)
- Lean Mixture (Vacuum Leak, etc.)
- Interruption in the Secondary Ignition Cable, 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 Cable, 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 for:







1. Fault Codes
2. Status Display
- Knock Control(active/not active)
3. Oscilloscope Display (Low DC Voltage-mV Setting)

When installing Knock Sensors:
DO NOT MIX THE CONNECTORS: Engine Damage will result! - the connector is critical to sensor location.
Do Not Over Tighten attaching bolt! - Piezo ceramic will be cracked. Torque to 20 nm.
Do Not Under Tighten attaching bolt, a loose sensor can vibrate producing a similar signal to a knock.