Fuel Control

ENGINE MANAGEMENT
This system employs a combination fuel injection/ignition system by Lucas/Marelli. The digital ignition system utilizes input devices and an ECM separate from the fuel injection system. The engine speed signal is sent from the Ignition ECM to the Fuel Injection ECM, (also referred to as EFI ECM).

ELECTRONIC FUEL INJECTION
The primary purpose of EFI ECM is to control fuel injection and related systems. To achieve precise regulation of fuel injection quantity, the EFI ECM factors into its calculations a variety of inputs, including coolant temperature, intake air temperature, engine load, throttle position, engine speed and battery voltage. Air/fuel adjustments are also made based on input from a pair of oxygen sensors in the exhaust system. By monitoring exhaust gas oxygen content, the EFI ECM can make accurate and rapid injector "ON" time adjustments needed for good performance and reduced emissions.

The EFI ECM also maintains control over idle speed, making compensating adjustments for temperature and engine load.

As a safety feature and to prevent flooding, EFI ECM circuitry prevents fuel pump operation unless the engine is running. When ignition is switched "ON," the pump runs for 2 seconds to pressurize the fuel rail in preparation for starting. When the engine is cranking or running, pump operation will resume. If the engine stalls, pump operation will cease.

Over-run Fuel Cut-off:

EFI ECM cuts off fuel injection during engine over-run, to improve fuel economy and aid in controlling exhaust emissions. ECM determines throttle is closed and engine speed is above 1100 rpm.

DIGITAL IGNITION

Ignition Control:

The Marelli digital ignition system is ECM controlled, eliminating both vacuum and mechanical advance mechanisms. Timing decisions, calculated by a microprocessor within the ignition ECM, are based on inputs from various engine sensors. The manifold absolute pressure (MAP) sensor is an integral ECM component. Microprocessor memory is programmed with a timing strategy for every engine speed and operating mode. The ignition ECM provides an engine speed (rpm) signal to the fuel injection (EFI) ECM.

The system utilizes two ignition coils, one for each cylinder bank. Current flow to coil primary circuits is regulated by two ECM controlled switching devices known as power modules or amplifier units.

Coil secondary output is routed to spark plugs through a double deck, two rotor distributor. BANK A (right) receives high voltage from the lower deck and BANK B (left) from the upper.

Bogus sensor input(s) will variously affect ignition system operation. However, the engine will not start without crankshaft position and engine speed inputs.

ECM sensor inputs form two groups of control parameters:

Primary Inputs
Crankshaft Position - TDC Sensor
Engine Speed - Engine Speed (Flywheel) Sensor
Engine Load - Manifold Absolute Pressure (MAP) Sensor

Correction Inputs
Throttle Position - Idle Switch
Coolant Temperature - Coolant Temperature Sensor
Intake Air Temperature - Air Temperature Switch

NOTE: Digital ignition system switches and sensors are not used or shared by the EFI system.

IDLE CONTROL
Idle control during A/C operation is accomplished by way of a supplementary air valve. This valve is not operated by engine management systems, but rather by the A/C relay. Refer to Powertrain Management/Fuel Delivery and Air Induction/Description and Operation.

SELF DIAGNOSIS
When the ECM detects a fault, the "CHECK ENGINE" lamp on the instrument cluster will illuminate. It will remain lit with ignition "ON" until the fault is corrected. A record of the fault is stored in ECM memory as a numbered code. Codes can be displayed on the trip computer.