Ignition ECM

PURPOSE
The ECU converts analog inputs into digital ignition timing outputs. Timing calculations are implemented through ECU control of two power modules. By regulating these switching devices, the ECU determines when spark plug firing occurs.

CONSTRUCTION
ECU is a computer with programmed microprocessor. The MAP sensor, providing engine load information, is an integral ECU component.

LOCATION

Ignition ECU:

In front passenger footwell.

PIN CONNECTIONS

Ignition ECU Pin Connections:

OPERATION
The ECU contains a microprocessor which converts analog inputs into digital ignition timing outputs. Microprocessor memory is programmed with an ignition timing strategy providing precision choices for every engine speed and mode of operation. The ECM also receives input signals from:

^ Air Temperature Sensor
^ Coolant Temperature Sensor
^ Engine Speed Sensor
^ TDC Sensor

None of the sensors are shared with EFI ECM.

Ignition ECM sends engine speed signals to EFI ECM.

During all operating modes, TDC sensor (crankshaft position) input is used by the ECU to program spark timing. Crankshaft position is referenced from BANK A (right) and entered into ECU timing calculations for all cylinders.

Timing during cranking and start-up is chosen from an ECU program linked to engine speed sensor and coolant temperature sensor inputs.

Timing during closed throttle operation is programmed separately for idle and deceleration. The ECU makes timing selections based on idle switch, engine speed and coolant temperature inputs.

When the idle switch is closed, the ECU does not recognize engine load (MAP sensor) input and chooses the idle portion of the ignition strategy. The ECU calculates refinements to basic strategy according to engine rpm and coolant temperature inputs.

Timing for open throttle running is calculated primarily from MAP sensor and engine speed inputs. ECU memory is programmed to make an optimum timing selection from any given combination of manifold pressure and engine speed. Correction inputs from coolant and intake air temperature sensors prompt ECU refinements to basic timing choices.