Diagnostics of ignition systems


How to perform diagnostics.

It is extremely difficult to analyze the ignition system of a modern car without access to an engine analyzer. The engine analyzer is capable of displaying ignition system waveforms and data such as firing voltage, spark voltage and burn time.


Parade.

Any malfunction in the ignition system, either in the primary or the secondary circuit will reveal itself in the appearance of the waveform. An example would be an open spark plug wire, a fouled spark plug or a spark plug with an improper spark gap. Other factors such as compression pressure, air/fuel ratio, engine RPM, throttle angle and manifold pressure will be apparent in the waveform, making it possible to diagnose problems that are external to the ignition system itself.


Ignition system problems may be constant such as a dead miss caused by an open spark plug wire, or intermittent such as a carbon tracked spark plug. Constant malfunctions care relatively easy to diagnose since the problem exists continuously. Intermittent problems may only be manifest during certain operating conditions such as heavy acceleration or at cruise speed. When diagnosing intermittent problems it will be necessary to re-create the conditions under which the malfunction is evident. The USB Autoscope III can be connected to a mobile computer such as a laptop or notebook. One technician drives the vehicle while another operates the oscilloscope from the passenger seat.

Different ignition systems may require different adapters.

How to perform diagnostics.


* Note: DIS has become a generic term, but initially was used to describe GM Distributorless Ignition systems.