The purpose of this test is to examine the individual signals in a 4-wire COP unit to identify the signals and verify correct operation.
This test involves measuring a potentially hazardous voltage.
Please ensure you follow manufacturers' safety instructions and working practices and ensure the rated voltage for all accessories you are using meets or exceeds the expected voltage.
Minimize the help page. You will see that PicoScope has displayed an example waveform and is preset to capture your waveform.
Use the Waveform Buffer, Zoom and Measurements tools to examine your waveform.
This test is for a 4-wire COP with a feedback signal to the ECU. Some 4-wire COPs have two ground pins and no feedback signal, these should be tested as a 3-wire COP please see 3-Wire COP Test.
The Example Waveform is showing the trigger signals from the coil selected on Channel A and the common feedback signal on Channel B.
Channel A. Trigger Signal.
The trigger signal rises from 0 V to about 4 V at coil switch-on and then returns to 0 V at coil switch-off. The time between these events is the dwell period or coil saturation time, determined by the Engine Control Module (ECM) or ignition amplifier.
Channel B. Feedback signal.
The feedback signal tells the ECM that ignition has occurred. The feedback signal on this engine is common to all four cylinders, so there are four feedback pulses for every engine cycle.
A 4-wire COP has the following connections, pin numbers may vary depending on the type of coil.
In addition to the trigger and feedback signals shown in the waveform above, it is sometimes useful to monitor the positive supply voltage and current and the ground voltage. For instructions on checking the supply and ground/earth pins, see the 3-wire COP test.
Positive supply voltage. This should be close to battery voltage. If it is low or absent then the ignition system is not receiving enough power and the coil will not function.
Ground. A small pulse will be seen on this signal during ignition as the coil draws current from the battery, but the pulse height should not exceed a few hundred mV. A larger voltage indicates too much resistance in the ground wiring, which could cause an ignition fault.
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