Description And Operation
DESCRIPTION
The fuel injection system inputs are made up of the following:
| 1. | Refer to INTAKE AIR TEMPERATURE (IAT) SENSOR . |
| 2. | Refer to THROTTLE BODY . |
| 3. | Refer to OXYGEN SENSOR . |
| 4. | Refer to FUEL INJECTORS . |
| 5. | Refer to MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR . |
| 6. | Refer to ACCELERATOR PEDAL POSITION SENSOR (APPS) . |
| 7. | Refer to CRANKSHAFT POSITION (CKP) SENSOR . |
| 8. | Refer to POWERTRAIN CONTROL MODULE (PCM) . |
OPERATION
Various sensors provide the inputs necessary for the PCM to correctly operate. The PCM continuously adapts to meet changing operating conditions and driving demands.
Fuel is injected into the intake port above the intake valve in precise metered amounts through electrically operated fuel injectors. Under most operating conditions, the PCM maintains an air fuel ratio of 14.7 parts air to 1 part fuel by constantly adjusting injector pulse width. Injector pulse width is the length of time the injector is open. The PCM adjusts the injector pulse width by opening and closing the ground path to each injector. Upstream Oxygen sensor feedback is the main input to fueling. Throttle input, engine speed, and MAP sensor feedback are contributing factors.
In order to maintain a 14.7 to 1 air fuel ratio the PCM regulates:
- Ignition timing
- Air/fuel ratio
- Emission control devices: MAP, BARO, O2, etc.
- Cooling fan
- Charging system
- Idle speed
- Vehicle speed control
The PCM also monitors the Fuel Injector system wiring for and related electrical faults.
| Refer to COMPONENT INDEX . |
Accelerator Pedal Position (APP) Sensor applications use Induction/Hall Sensors (non-contact). The Electronic Throttle Control (ETC) system uses two APPS to monitor the accelerator pedal position. The APPS sensors 1 and 2 are integrated into one assembly located at the pedal assembly. Each sensor has a 5-volt reference circuit, a low reference circuit, and a signal circuit. The PCM reads the two signals individually and then compares the two signals as a redundant check of the pedal position. One of the sensors will fluctuate somewhere between 0 volts and 5.0 volts and the other sensor will fluctuate somewhere between 0 volts and 2.5 volts. The fluctuation of the two sensors should move proportionately. When operating properly, the voltage reading of the sensor operating on the 2.5 volt scale will always be approximately half of the voltage reading of the sensor on the 5.0 volt scale. The signal for APP 2 is also used by the PCM for an internal ground check. This test runs a couple of times per second and is the reason why the APP 2 signal spikes to ground regularly during normal operation.
| Refer to COMPONENT INDEX . |
Engine speed and crankshaft position are provided through the CKP sensor. The sensor generates pulses that are the input sent to the PCM. The PCM interprets the sensor input to determine the crankshaft position. The PCM then uses this position, along with other inputs, to determine injector sequence and ignition timing. The sensor is a hall effect device combined with an internal magnet. It is also sensitive to steel within a certain distance from it. A tone-wheel (target wheel) is bolted to the crankshaft. This tone-wheel has 57 regular teeth and one long tooth (signature area). The valleys cause a pulse to be generated when they pass under the sensor. The pulses are the input to the PCM.
| Refer to COMPONENT INDEX . |
The fuel injectors are electrical solenoids. The injector contains a pintle that closes off an orifice at the nozzle end. When electric current is supplied to the injector, the armature and needle move a short distance against a spring, allowing fuel to flow out of the orifice. The spraying action atomizes the fuel, adding it to the air entering the combustion chamber. An individual fuel injector is used for each individual cylinder. The top (fuel entry) end of the injector is attached into an opening on the fuel rail. The nozzle (outlet) ends of the injectors are positioned into openings in the intake manifold just above the intake valve ports of the cylinder head.
The Fuel Injectors are supplied voltage from the Automatic Shut Down (ASD) relay output circuit. The PCM controls the operation of the injectors through a Pulse Width Modulated (PWM) Low Side Driver (LSD). Each injector receives a unique pulse width based on that cylinder's fuel requirements. The PCM determines this fuel requirement by monitoring engine operating parameters through various sensors and then calculating the appropriate amount of fuel to be injected. The optimum amount of injected fuel depends on conditions such as engine and ambient temperatures, engine speed and workload, and oxygen sensor feedback.
| Refer to COMPONENT INDEX . |
The 2-wire manifold IAT sensor is installed with the sensor element extending into the air stream. The IAT sensor is a two-wire Negative Thermal Coefficient (NTC) sensor. Meaning, as inlet air temperatures increase, resistance (voltage) in the sensor decreases. As temperature decreases, resistance (voltage) in the sensor increases. The IAT sensor provides an input voltage to the PCM indicating the density of the air entering the intake manifold based upon intake manifold temperature. The PCM provides the sensor with a 5 volt signal and clean sensor ground.
| Refer to COMPONENT INDEX . |
The MAP sensor mounts to the upper intake manifold near the throttle body. The MAP Sensor is a transducer that varies resistance according to changes in intake manifold pressure. The PCM supplies 5 volts to the MAP Sensor on a 5-Volt reference circuit and provides a ground on a low reference circuit. The MAP Sensor provides a voltage signal to the PCM on a signal circuit relative to the pressure changes.
| Refer to COMPONENT INDEX . |
This vehicle has 4 switching O2 sensors. The four wire O2 sensors are attached to and protrude into the vehicle exhaust system. This emissions system uses a total of four sensors. The two upstream sensors are referred to as 1/1 and 2/1, the two downstream sensors are referred to as 1/2 and 2/2. The left and right upstream sensors (1/1 and 2/1) are located in the left and right exhaust down-pipes just before the catalytic convertors. The left and right downstream sensors (2/1 and 2/2) are located in the left and right catalytic convertors. Normal range of the O2 sensor output is a 0 to 1.0 volt analog to digital signal when the sensor is in normal operating temperature range. When the oxygen content is high (caused by a lean air/fuel mixture) the sensor produces a low voltage. When the oxygen content is low (caused by a rich air/fuel mixture) it produces a higher voltage.
| Refer to COMPONENT INDEX . |
The PCM is located next to the washer solvent reservoir. The PCM is a digital computer containing a micro-controller. The PCM receives input signals from various switches and sensors that are referred to as PCM inputs. Based on these inputs, the PCM adjusts various engine and vehicle operations through devices that are referred to as PCM outputs. The PCM uses the Controller Area Network-Chassis (CAN-C) bus to perform engine diagnostics and flash operations.
By monitoring the exhaust oxygen content through the oxygen sensors and all other inputs, the PCM has the ability to fine tune the air handling, fuel control, ignition timing and spark advance settings. This is done to achieve optimum fuel economy combined with low emission engine performance.
| Refer to COMPONENT INDEX . |
The throttle body mounts to the intake manifold. The throttle position sensor and ETC Motor are integral to the throttle body. The throttle body is a non-serviceable assembly. The throttle blade will not close completely when the engine is shut down. This engine off, slightly open blade position is for start-up. The electric throttle body will also adjust the throttle blade for normal driving operation. The ETC motor is controlled using an H-Bridge circuit inside the PCM. An H-Bridge is an electronic circuit that enables a voltage to be applied across a load in either direction.