What It Is

How It Works

The ECU receives power from the vehicle battery when the ignition is set to the ON
position. During cranking and engine operation, the following events occur.
 (1) Signals Received

The following information is received from the EFI components:

1.  Engine Coolant Temperature

2. Intake Manifold Air Temperature

3. Intake Manifold Air Pressure

4. Engine Speed

5. Throttle Position

6. Commands Issued

The following commands are transmitted by the ECU:

1.  Electric Fuel Pump Activation

2. Air Solenoid Valve Activation

3. Injection Valve Activation

 The desired air/fuel ratios for any combination of possible driving and atmospheric conditions are programmed into the ECU at the factory. As the above signals are received from the operating components,  the ECU processes the signals and computes the engines fuel requirements. The ECU then issues commands to the
injection valve to open for a specific time duration (milliseconds).

The duration of the command pulses varies as the operating condition change. The injection valves are separated into two groups, of two injectors each. Both injection valves in each group open simultaneously upon command during normal operation.

During wide open throttle operation, all four injection valves open simultaneously upon command by the ECU.

Due to the complexity of the ECU electronics, the Diagnostic
Analyzer (Figure 2-1) does not perform direct ECU tests. Instead, the analyzer tests all other EFI components, and voltage inputs for failure.

The Diagnostic Analyzer, however, contains a supplemental ECU that will operate the engine, providing of course, that other components are functioning properly. Thus, by process of elimination, a malfunctioning ECU will be identified.

SYSTEM OPERATION

Figure 1-5 (Above) presents a functional block diagram of the EFI System, depicting signal inputs and outputs.

The average starting time for a cold engine with electronic fuel injection is two (2) seconds. In extreme cold conditions it may be necessary to crank the engine for four (4) seconds. The accelerator should not be depressed when starting the vehicle, this will defeat the pre-programmed functions and delay starting.

The Electronic Control Unit is activated by the vehicle battery when the ignition switch is turned to the ON position. The following events occur at that time:

1. The Air Solenoid Valve is activated
   

2. The Fuel Pump is activated - (The pump will operate for approximately one second unless the engine is cranked and operated.)
   

3. All engine sensors are activated and begin transmitting signals.

The following events occur when the ignition is set to START POSITION and the engine cranks warms, and is driven:

(1) The fuel pump is activated for continuous operation

(2) The Fast Idle Valve senses the engine coolant fluid temperature and provides an additional, controlled amount of air to the intake manifold during engine warm-up.

(3) The Air Solenoid Valve provides supplementary air to the intake manifold in a relationship to engine speed and temperature, to control engine rpm during warm-up.

(4) The Throttle Body air-bypass controls the air flow to the intake manifold with the throttle valves closed. The throttle valves, which are controlled by the accelerator pedal, control the air flow to the intake manifold for driving.

(5) The Fuel Pressure Regulator maintains the fuel pressure in the fuel rail at 39 psi higher than the intake manifold air pressure and allows unused fuel to return to the fuel tank.(6) The following signals are continuously received and processed by the Electronic Control Unit:

(7) The Electronic Control Unit receives the above information in the form of electrical signals. The signals are continuously computed, and controlled electrical pulses are transmitted to the injectors to precisely control the fuel being injected into the cylinder. Since the EFI System is a two-group system, the pulses are timed to activate two injectors (one group) at one time.