INSPECTION PROCEDURE USING AN OSCILLOSCOPE

1.Disconnect the inlet camshaft position sensor connector and insert the special tool test harness (MB991709) in-between the separated connectors. (Always mate all the terminals.) 2.Disconnect the crank angle sensor connector and insert the special tool test harness (MB991709) in-between the separated connectors. (Always mate all the terminals.) 3.Connect the probe of each channel of the oscilloscope to terminal No. 3 of the inlet camshaft position sensor connector and terminal No. 3 of the crank angle sensor connector, respectively.

Description of Wave Patterns

• The inlet camshaft position sensor serves as to detect the compression top dead center of each cylinder. By observing this signal simultaneously with the crank angle sensor signal, it is possible to identify each cylinder.
  
• The crank angle sensor is used to detect the crank angle of each cylinder. While the engine revolves for two cycles, 72 pieces of the crank angle sensor signal (including any missing) will be outputted.
  
• The engine ECU carries out the engine control, using the fall signal (from 5 to 0 V) of the crank angle sensor. The rise signal (from 0 to 5 V) position does not affect the control.
  

Wave Pattern Observation Points

• Verify that the sensor signal frequency increases as the engine speed rises.
  

Example 1 Wave pattern characteristics Rectangular wave will be outputted while the engine is not started. Cause of problem Failed sensor interface

Example 2 Wave pattern characteristics Wave pattern is displaced in the forward or backward direction. Cause of problem Loose timing chain Abnormal sensing section

1.Disconnect the exhaust camshaft position sensor connector and insert the special tool test harness (MB991709) in-between the separated connectors. (Always mate all the terminals.) 2.Disconnect the crank angle sensor connector and insert the special tool test harness (MB991709) in-between the separated connectors. (Always mate all the terminals.) 3.Connect the probe of each channel of the oscilloscope to terminal No. 3 of the exhaust camshaft position sensor connector and terminal No. 3 of the crank angle sensor connector, respectively.

• The exhaust camshaft position sensor serves as to detect the position of the exhaust camshaft and outputs one pulse per revolution of camshaft corresponding to the cut provided on the exhaust-side camshaft.
  
• The wave pattern of the exhaust camshaft position sensor moves in the retard angle direction from the most advanced angle position when the low load operation changes to the high load operation.
  

Example 1 Wave pattern characteristics Rectangular wave will be outputted while the engine is not started. Cause of problem Failed sensor interface

Example 2 Wave pattern characteristics Wave pattern is displaced in the forward or backward direction. Cause of problem Loose timing chain Abnormal sensing section

1.Disconnect the injector connector and insert the special tool Test harness (MB991658) in-between the separated connectors. (Always mate all the terminals.) 2.Connect the oscilloscope probe to terminal No. 2 of the injector connector.

• Normally the power supply voltage is shown. When the engine-ECU outputs the injector drive signal ON, the voltage falls to approximately 0V during the period of the signal ON. (See Point B.)
  
• When the engine-ECU stops the output of the injector drive signal, the voltage peak appears due to the counter electromotive force of the coil. (See Point A.) And then the power supply voltage returns to its normal value.
  
• Injector operation time: fuel injection period determined by engine-ECU according to various sensor output values. Injector operation time = effective injection period + invalid injection period (invalid injection period: compensation of injector response delay due to decrease in power supply voltage)
  
• Counter electromotive force of solenoid coil: the counter electromotive force is created in the injector coil when the engine-ECU stops the output of the injector drive signal.
  
• Power supply voltage: the power supply voltage is shown when the engine-ECU stops the output of the injector drive signal ON. If this supply voltage is low, the injector operation time becomes longer as the invalid injection time becomes longer.
  

Point B: Injector operation time Operation time Consistent with the displayed time on M.U.T.-III. Force an excessive acceleration. The drive period will once extend greatly, then will be settled to that corresponding to the engine speed.

1.Disconnect the ignition coil connector and insert the special tool test harness (MB991658) in-between the separated connectors. (Always mate all the terminals.) 2.Connect the oscilloscope probe to terminal No. 2 of the ignition coil connector. 3.To verify the ignition advance angle, observe it simultaneously with the crank angle sensor output signals.

Description of Wave Patterns

• Power transistor ON condition:
  An interval when the power transistor is ON and the primary side of ignition coil is conducted (referred to as "dwell interval") This conduction period gets longer if the battery voltage is low or vice versa so that the primary voltage at ignition can be controlled to a constant level.
  
• Power transistor OFF condition:
  This interval corresponds to when the power transistor is OFF and the power transistor drive signal is not outputted from the engine-ECU.
  

Wave Pattern Observation Points

• Verify that the power transistor control signal (ignition timing) advances as the engine speed increases.
  

Wave pattern characteristics The voltage is low. Cause of problem Open-circuit in the ignition primary circuit.