Plug a BNC test lead into Channel A on the PicoScope, place a black clip onto the test lead with the black moulding (negative) and a Back-pinning Probe onto the test lead with the red moulding (positive). Place the large black clip onto the battery negative terminal and probe one of the Electronic Control Module's (ECM) coil inputs with the Back-pinning Probe. Plug a BNC test lead into Channel B, and a Back-pinning Probe onto the test lead with the red moulding (positive) probe the coil pack's other ECM input with the probe.
When these connections are made, the dwell angle and ignition primary pictures will not be displayed as they would on a conventional Distributorless Ignition System (DIS) system. This particular system is used on the GM/Vauxhall/Opel ECOTEC 1.6 Lt. Multec system has an integral amplifier with no external primary connections, making diagnostics somewhat difficult.
This oscilloscope set up can also be used on other external amplifier systems that are switched by an ECM.
Figure 1 shows the two acupuncture probes 'back probing' the coil multi-plug. Due to access the illustration shows the multi-plug disconnected.
The double ended coil differs from many other systems as it has the ignition amplifier built into the coil pack. The coil/amplifier pack will have 4 electrical connections. The pack receives a 12 volt supply from the ignition switch, has an independent earth return and the remaining two connections are in the form of a 5 volt 'squarewave' digital signal from the Electronic Control Module (ECM).
The ECM will receive information from the engine's sensors and calculates the point of ignition by the ECM from its internal pre-set parameter. At the designated point, the 5 volt supply drops to zero volts, signalling the amplifier to remove the earth path on the coil primary, firing the coil.
The coil/amplifier pack has two separate sides (one for cylinders 1 + 4 and the other for cylinders 2 + 3). Using an oscilloscope with dual trace both circuits can be monitored and it can be seen that the coils are fired alternately, as the example shows.
This particular system that is fitted to the 1.6 litre GM/Vauxhall/Opel ECOTEC engine has the ignition amplifier as an integral part of the coil pack.
This particular configuration is a hindrance to those of us who perform diagnostic tuning, as the system does not allow for any connections to the low tension circuit. When the two outer electrical connections are monitored with an oscilloscope a digital square wave is seen and not the expected primary parade picture. The integral coil pack with the built in amplifier will have a voltage supply on the centre terminal at 12 volts with two 5 volt square wave signals to switch the pair of coils.
If the coil's switching is faulty due to a lazy power transistor and the 'normal' induced voltage is reduced, this would, in normal circumstances, be easily seen but with this combination the only clue would be in a reduced spark duration and coil output.
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.
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