Digital ECM to Ignition Amplifier Signal Diagnostics (Vauxhall ECO
TEC 1.6 Lt. Multec)
ended coil in this particular case, 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.
coil/amplifier pack has two separate sides (one for cylinders 1 + 4 and the
other for cylinders 2 + 3).
particular system is fitted to the 1.6 litre Vauxhall ECO TEC engine and has
the ignition amplifier as an integral part of the coil pack.
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