Ignition Control Module: Description and Operation

Ignition Module Location:

Ignition Module Pinout:

DESCRIPTION
The ignition control module counts the time between zero crossing events of the crankshaft position sensor to determine the engine speed and locate the odd pulse. To determine when the odd pulse occurs, the module compares the time intervals between zero crossings. When the time measurement is less than one-fourth of the previous interval and less than one-third of the following interval, then the module recognizes that the crankshaft position sensor was at the odd slot.

With this input, the module outputs a signal to the Engine Control Module (ECM) for determination of engine speed and position. This is a 0 to 5 volts square wave signal called reference high. The reference signal is transitioned to a high state at every other slot / sensor alignment, which is 6 degrees BTDC of each cylinder.

It stays in this high state until the next slot which is also 6 degrees BTDC at which time it falls to a low state. Thus, the repeated cycle for an eight cylinder is when the reference goes high for 45 degrees then low for 45 degrees.

Once the ignition control module determines the position of the engine from the crankshaft position sensor signal, it must select which of its ignition coils to charge.

The coils are wired such that cylinder pairing between two cylinders which are at TDC simultaneously occurs. For instance, on a typical 8 cylinder, engine cylinders 1 and 6 are paired. When one is at TDC exhaust, the other is at TDC compression. The pairing allows one coil to fire 2 spark plugs in series since one cylinder requires a high voltage for spark (compression) and the other requires low voltage (exhaust). The ignition control module can then charge and fire separate coils for its voltage distribution.

IDENTIFICATION
There are four connectors at the ignition control module that have to be disconnected in order to remove the upper air inlet plenum. The largest connector, referenced as number one, is the 14 pin ECM harness connector.

Connector numbers two and three contain the primary coil drivers for the four coil pairs. Terminal "C," which is at the outboard edge of each of the connectors is system ground (engine ground).

Connector number four is from the magnetic crankshaft position sensor. The middle wire of connector is a drain lead. The drain lead has no insulation and makes contacts with an aluminum foil, which wraps around the crankshaft position sensor leads. This is used to suppress any electromagnetic inductive pulses that might pass through the crankshaft position sensor leads. The high (+) and low (-) sensor leads are the remaining two leads that make up the number four connector. The connectors number two and three are keyed so they will not connect to the wrong connector on the ignition control module.