Starting in 1997, General Motors used a new (for them) coil-near-plug
ignition system for the then new Corvette LS1 engine. The system
features eight coils (one per cylinder) mounted on the valve cover,
with short spark plug wires to connect the coils to the spark plugs.
The General Motors LS1 coils are not just conventional ignition coils.
Instead they are complete single-cylinder ignition systems. They
contain all the electronics for dwell limiting, current limiting, etc. These
coils are controlled directly by a low voltage, low current signal from
the sequencer. There is no intervening ignition module (like an EDIS or
GM DIS). Because the LS1 coils have the igniters built in, they make for
an easy installation and generate less electromagnetic noise in the
other wiring under the hood.
Over deze LS2/Truck bobines:
The LS2 coil-near-plug coils are similar in form and function to the LS1
coils described above.
The LS2/truck coil has a visible external aluminum heat sink near the
These LS2 coils are incredible. Even compared to the LS1 coil,
these are just crushers!
On the LS1 coil there is around 40 milliamps of peak secondary current
with 5 milliseconds of dwell time.
On the LS2/truck coil (AC Delco D585), there is 120 milliamps!
Hoe te gebruiken:
The LS2 coil has 4 connections (as well as the high tension terminal
for the spark plug wire, of course):
A = Coil Primary Ground
B = Ignition low noise ground from ECU (ground)
C = Ignition digital signal from ECU (+5V)
D = +12V Supply to Coil Primary
The two capacitors are optional but recommended. The 1.0 µF capacitor
on the +12V is helpful, it is similar to the one used on EDIS. What it
does is provide brief energy storage for the discharge. The other
capacitor will help eliminate back-fed noise to the MegaSquirt controller.
Use a 100 pF to 0.001 µF cap on the TTL trigger input wire to ground.
What this does is shunt extremely fast noise spikes to ground and not
let them feed back to the MegaSquirt processor. The added capacitance
is minimal - with the series resistance of 1,000 ohms (in the controller)
and a 100 pF capacitor the RC 3dB time constant is 2πR × C = 0.6 microseconds.
The LS2 built in coil igniters (the amplifier that drives the coil's primary
current based on the sequencer signal) will follow the sequencer signal
pulse width. When the signal from the sequencer is high (3 to 5+ Volts -
with very little current from the controller, a few dozen milliAmps), the coil
current will be building. When the signal from the sequencer is pulled low
(shut off), the coil will spark. The duration of the signal from the megasquirt /
sequencer determines the dwell (though the coil igniter limits this to no more
than ~8 milliseconds).
The dwell should be set at 5 milliseconds input pulse trigger - going longer
does not generate any more spark current.
To get 5.0 milliseconds of running dwell, the nominal dwell parameters should
be set to:
- Maximum Dwell5.5 milliseconds
- Maximum Spark Duration2.0 milliseconds
- Acceleration Compensation0.5 milliseconds
Battery Voltage Compensation
Setting Net Voltage Dwell Compensation
-4.0 8.0 Volts 2.4 milliseconds
-2.0 10.0 Volts 0.9 milliseconds
0.0 12.0 Volts 0.0 milliseconds
2.0 14.0 Volts -0.5 milliseconds
4.0 16.0 Volts -0.9 milliseconds
This will give 5.5 - 0.5 = 5.0 milliseconds at 14.0 volts while running with the
alternator charging normally.
Here is a video of the coil in action - with the LS1 on the test stand you can
hear the sparking, not loud but certainly audible. With the LS2/truck coil it
sounds like someone is banging on the table! The big resistor you see in the
video is part of a voltage divider setup. Its value is 100 megaohm (R1), in
series with a 100 Kohm (R2), this pair is across the spark plug. The voltage
across the 100 Kohm resistor is what is viewed on the scope.