Engine Electronics: Diagnosis BMW 3 series E36

Power Supply - Testing

Inadequate power and ground supply can result in

1. No Start
2. Hard Starting (Long Crank Times)
3. Inaccurate Diagnostic Status or ECM Not Found
4. Intermittant/Constant Check Engine Light
5. Intermittant/Constant Driveability Problems

Testing Power Supply. Scheme 22

Power supply including fuses should be tested for

1. Visual (1) Blown Fuse
2. Available Voltage 2
3. Voltage Drop (Dynamic Resistance) (2)
4. Resistance of Cables and Wires (2)

Testing Power Supply Fuse. Scheme 23

The ignition (KL15) must be switched off when removing or installing the ECM connector to prevent voltage spikes (arcing) that can damage the Control Module!

The Engine Control Module Relay (located in the fuse box) should be tested for

1. Battery Voltage and Switch Ground (1)
2. Resistance (1)
3. Battery Voltage and Voltage Drop (2)

Identifying Engine Control Module Relay. Scheme 24

Throttle Position Sensor - Testing

The Throttle Position Sensor (potentiometer) can be tested with the following methods

1. DIS Status Page (approx. 0.6v idle to 4.2v full throttle).
2. DIS Oscilloscope - Select from the Preset Measurements which requires taking the measurement with the ECM and Universal Adapter connected to the circuit.
3. Resistance check of the entire circuit, using the Universal Adapter with the ECM disconnected (approx. 1-4 K ohms).

Checking Throttle Position Sensor. Scheme 25

Idle Speed Control Valve - Testing

1. The Idle Speed Control Valve and idle air circuit (passage ways) should be checked for physical obstructions.
2. The resistance of the valve winding should be checked (8 +/-2 ohms).
3. The ECM output and Idle Speed Control Valve operation can be tested by "Component Activation" on the DIS/MoDIC.
4. The Pulse Width Modulated ground output from the ECM can be tested using the DIS/ MoDIC Oscilloscope.

Testing Idle Speed Control Valve. Scheme 26

Air Flow Volume Sensor - Testing

The Air Flow Volume Sensor (potentiometer) can be tested with the following methods

1. DIS Status Page (Up/Uv Ratio 0.1 - 0.3 at idle speed).
2. DIS Oscilloscope - Select from the Preset Measurements which requires taking the measurements with the ECM disconnected and the Universal Adapter connected to the circuit.
3. Resistance check of the entire circuit, using the Universal Adapter with the ECM disconnected.

Testing Air Flow Volume Sensor. Scheme 27

Air Temperature Signal - Testing

NTC sensors decrease in resistance as the temperature rises and vice versa. The ECM monitors the sensor voltage which varies as temperature changes the resistance value. For example, as temperature rises

1. Resistance through the sensor decreases.
2. Voltage drop across the sensor decreases.
3. Input signal voltage also decreases (5-0v).

Testing Air Temperature Signal. Scheme 28

1. DIS/MoDIC Status page.
2. DIS/MoDIC Multimeter At 20° C 2.2 - 2.7 k ohms

DISA - Testing

The DISA System can be tested by raising the RPM to 4,840 (briefly) and visually checking the Vacuum Motor Actuator Arm for movement.

If the Actuator Arm does not move, repeat test and check for vacuum at

1. Vacuum Motor
2. Solenoid Valve
3. Reservoir

Repeat the test to verify the ECM is providing a ground signal to the Solenoid Valve.

Checking DISA Solenoid Valve. Scheme 29

Fuel Pump/Pressure Regulator - Testing

The fuel pump should be tested for delivery pressure and volume. Caution when disconnecting fuel hoses because there is the possibility of residual fuel pressure! Install the fuel pressure gage between the fuel filter and pressure regulator.

Remove the fuel pump relay (see relay testing in the POWER SUPPLY section) and connect the Relay Bypass Switch to pin 87b and 30 of the relay socket. This will activate the fuel pump without running the engine.

Testing Fuel Pump/Pressure Regulator. Scheme 30

Fuel volume must be tested to verify

1. Fuel Pump Output
2. Restriction are not present in the pump pickup lines/hoses and fuel filter

Testing Fuel Volume. Scheme 31

Ignition System Diagnosis

A fault survey should first be performed using the DIS/MoDIC 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

1. Power Supply at the Coil (KL15)
2. Resistance of the harness and ignition coil primary winding (terminal 15 to 1 approximate 0.8 ohms) - using the 88 Pin Adapter with the ECM Disconnected

Diagnostic Ignition System. Scheme 32

1. ECM Primary Circuit Final Stage Transistor
2. ECM Ignition Coil (one of four)
3. Secondary Coil Ground
4. ECM Final Stage transistor activation. This test function is found under the Oscilloscope Preset list - "Ignition Signal Primary" (normal Terminal 1 Signal).

Install the 88 Pin 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 running.

If there is a fault in the secondary ignition, testing should include

1. Primary Ignition
2. Evaluation of Secondary Oscilloscope Patterns

The Following are Examples of Secondary Oscilloscope Patterns

This is a normal pattern for one ignition circuit with the engine at idle speed.

1. Normal Combustion Period
2. Normal Ignition Voltage Peak

Identifying Secondary Oscilloscope Patterns (1 Of 6). Scheme 33

Long Spark Period (1) with Low Ignition Voltage Peak (2)

1. Indicates Low Compression

Identifying Secondary Oscilloscope Patterns (2 Of 6). Scheme 34

If Spark Period is Fluctuating

1. Contamination on Spark Plug or Defective Spark Plug

Short Spark Period (1) with High Ignition Voltage Peak (2).

1. Defective Ignition Cable, Connector, or Resistive Adapter Boot

Identifying Secondary Oscilloscope Patterns (3 Of 6). Scheme 35

Evaluation of Ignition Voltage Peaks at Idle Speed (All Cylinders Displayed).

1. Normal Attenuation (Voltage Reduction) Process
2. Shorten Attenuation Process-Defective Ignition Coil
3. Absence of Attenuation - Defective Ignition Coil

Identifying Secondary Oscilloscope Patterns (4 Of 6). Scheme 36

No Sparking Voltage Line (Single Cylinder Displayed)

1. Defective Ignition Coil

Identifying Secondary Oscilloscope Patterns (5 Of 6). Scheme 37

Evaluation of Ignition Voltage Peaks under Sudden Loads (All Cylinders Displayed).

1. Decaying Process is not much Higher than Ignition Voltage Peak - System is Ok.
2. Decaying Process is considerably Higher than Ignition Voltage Peak
3. Lean Mixture
4. Defective Fuel Injector
5. Low Compression

Identifying Secondary Oscilloscope Patterns (6 Of 6). Scheme 38

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)

1. Spark Plug Gap is to Large (Worn or Burned)
2. Incorrect Heat Range Spark Plug
3. Compression is too High (Carbon, etc.)
4. Lean Mixture (Vacuum Leak, etc.)
5. Interruption in the Secondary Ignition Cable, Connector, or Resistive Adapter Boot

If the Secondary Ignition Voltage is Too Low (Low Resistance for Ignition)

1. Spark Plug Gap is Too Small (Mishandled on Installation)
2. Incorrect Heat Range Spark Plug
3. Compression is Too Low
4. Voltage Leak in the Secondary Ignition Cable, Connector, or Resistive Boot to Ground