Input Components

The fuel control system consists of the ECU outlined previously and various input and output components. The input components relay data to the ECU regarding engine operating conditions. The following is a list and description of the input components:


Manifold Absolute Pressure (MAP) Sensor

The MAP sensor reacts to absolute pressure in the intake manifold. Manifold pressure supplies mixture density and ambient barometric pressure information to the ECU. The MAP sensor provides data to the ECU regarding this density and pressure in the form of input voltage.


Coolant Temperature Sensor (CTS)

Located in the intake manifold coolant jacket, the CTS provides engine coolant data to the ECU. When low coolant temperature data is observed, the ECU will: enrich the air/fuel mixture, compensate for fuel condensation in the intake manifold, control warm-up idle speed, increase ignition advance and inhibit EGR system operation.


Manifold Air/Fuel Temperature (MAT) Sensor

This sensor, located in the intake manifold, supplies air/fuel mixture temperature data to the ECU. The ECU will then compensate for air density changes during high temperature operation.


Oxygen Sensor

This sensor, located in the exhaust pipe, supplies voltage data to the ECU depending on the oxygen content in the exhaust gas. The ECU uses this data to vary the air/fuel ratio accordingly. The sensor used on 4-150 engines is equipped with a heating element that keeps the sensor at proper operating temperatures during all operating modes. This enables the system to enter closed loop operation sooner and remain in closed loop mode during periods of extended idle. The feed circuit to the oxygen sensor is through the ignition switch.


Battery Voltage

Battery voltage data is used by the ECM to ensure that proper voltage is applied to the fuel injector at all times. The ECU varies the voltage applied to compensate for battery voltage fluctuations.


Speed Sensor

Attached to the flywheel/drive plate housing, this sensor provides engine speed and crankshaft angle data to the ECU. The flywheel/drive plate has a large trigger tooth and notch located 90 degrees and 12 small teeth before each top dead center (TDC) position. When a small tooth and notch pass the magnetic core of the sensor, the magnetic field collapses, causing a low voltage spike in the sensor pickup coil winding. These voltage spikes enable the ECU to count the teeth as they pass the sensor. When a large trigger tooth and notch pass the magnetic core of the sensor, the magnetic field again collapses, inducing a higher voltage spike in the sensor pickup coil winding. This higher spike indicates to the ECU that a piston will be at TDC 12 teeth later. The ignition timing is then either advanced or retarded as necessary.


Starter Relay

The starter relay provides input data to the ECU that indicates that the starter motor is engaged.


Closed Throttle (Idle) Switch

This switch is an integral part of the idle speed actuator(ISA) motor and provides input data to the ECU that will enable it to either increase or decrease the throttle stop angle in response to various engine operating conditions.


Throttle Position Sensor (TPS)

Mounted on the throttle body assembly, this sensor provides an input signal of up to 5 volts to the ECU regarding throttle position. At idle speed, an input signal of approximately 1 volt is transmitted to the ECU. As throttle opening increases, a corresponding increase in the voltage signal to the ECU is observed, to a maximum of 5 volts.


Wide Open Throttle (WOT) Switch

Attached to the side of the throttle body, this switch provides input data to the ECU regarding when a wide-open throttle condition exists. The ECU then enriches the air/fuel mixture accordingly.


Power Steering Pressure Switch

During periods of high pump load and low engine RPM (parking maneuvers), the power steering pressure switch contacts close, transmitting this data to the ECU. The ECU then raises idle speed to accommodate the increased load on the engine from power steering pump operation.


Load Swap Relay

Used on vehicles with air conditioning and power steering, this relay works in conjunction with the power steering pressure switch. If the compressor clutch is engaged when the pressure switch contacts close, the input signal from the switch to the ECU also activates the load swap relay. The relay contacts then open, cutting off the electrical feed to the compressor clutch. The clutch will remain disengaged until the pressure switch contacts reopen and engine idle returns to normal.


A/C Controls

These controls indicate to the ECU that the A/C switch is in the On position. The ECU will then engage the compressor clutch and change idle speeds as required.


Transmission Gear Position Indicator

Used on some vehicles equipped with automatic transmission, this device provides input data to the ECU indicating that the vehicle is in a driving mode.