INSPECTION PROCEDURE USING AN OSCILLOSCOPE

1.Disconnect the camshaft position sensor connector and connect the special tool test harness (MB991709) in between (All terminals should be connected). 2.Connect the oscilloscope special patterns pickup to camshaft position sensor terminal No. 2. 3.Disconnect the crank angle sensor connector and connect the special tool test harness (MD998478) in between. 4.Connect the oscilloscope special patterns pickup to crank angle sensor terminal No. 2.

Description of Wave Patterns

• The intake camshaft position sensor serves as to detect the compression top dead center of each cylinder. By observing this signal simultaneously with other control signals, 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 crank angle sensor High signal (including any missing) will be outputted.
  

Wave Pattern Observation Points

• Verify that the wave pattern is shortened 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 belt 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 supply voltage is applied, but, if any signal is received from the engine-ECU <M/T> or engine-A/T-ECU <A/T>, the voltage falls to near 0 V as long as the drive signal continues.
  
• When the signal from the engine-ECU <M/T> or engine-A/T-ECU <A/T> is stopped, a peak voltage resulting from the counter electromotive force of coil appears and the original supply voltage restores.
  
• Injector operation time: Fuel injection period determined by the engine-ECU <M/T> or engine-A/T-ECU <A/T> according to various sensor output values. Injector operation time = Effective injection period + Invalid injection period (invalid injection period: used to compensate for the delayed operation due to decrease in the supplied voltage)
  
• Counter electromotive force in the solenoid coil: When the signal from the engine-ECU <M/T> or engine-A/T-ECU <A/T> is OFF, the injector coil can generate a counter electromotive force (Approximately 50 to 60 V).
  
• Power supply voltage: While there is no signal from the engine-ECU <M/T> or engine-A/T-ECU <A/T>, the supply voltage is applied.If this supply voltage is low, the invalid injection period gets longer, and the drive period gets longer as well.
  

Point A: The level of counter electromotive force of solenoid coil: Solenoid coil counter electromotive force is low or doesn’t appear at all. Short-circuit in the injector solenoid 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 <M/T> or engine-A/T-ECU <A/T>.
  

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.