Part 2

Part 2 of 3

Continued From Part 1 Part 1

Fuel Systems
Mechanical Returnless Fuel SystemThe fuel system consists of a fuel tank with reservoir, fuel pump, fuel pressure regulator, fuel filter, fuel supply line, fuel rail, fuel rail pulse damper, fuel injectors, and Schrader/pressure test point. Operation of the system is as follows:

1. The fuel delivery system is enabled during crank or running mode once the PCM receives a crankshaft position (CKP) sensor signal.

2. The fuel pump logic is defined in the fuel system control strategy and is executed by the PCM.

3. The PCM grounds the fuel pump relay, which provides VPWR to the fuel pump.

4. The inertia fuel shut-off (IFS) switch is used to de-energize the fuel delivery secondary circuit in the event of collision. The IFS switch is a safety device that should only be reset after a thorough inspection of the vehicle (following a collision).

5. A pressure test point valve (Schrader valve) is located on the fuel rail. This is used to measure fuel injector supply pressure for diagnostic procedures and repairs.

6. Located on the fuel rail is a pulse damper. The pulse damper reduces fuel system noise caused by the pulsing of the fuel injectors. The vacuum port located on the damper is connected to manifold vacuum to avoid fuel spillage in the event the pulse damper diaphragm were to rupture (the pulse damper should not be confused with a fuel pressure regulator).

7. The fuel injector is a solenoid-operated valve that meters the fuel flow to each combustion cylinder. The fuel injector is opened and closed a constant number of times per crankshaft revolution. The amount of fuel is controlled by the length of time the fuel injector is held open. The injector is normally closed and is operated by 12 volt VPWR from the power relay. The ground signal is controlled by the PCM.

8. There are three filtering or screening devices in the fuel delivery system. The intake sock is a fine, nylon mesh screen mounted on the intake side of the fuel pump. There is a fuel filler screen located at the fuel rail side of the fuel injector. The fuel filter assembly is located between the fuel pump and the pressure test point/Schrader valve.

9. The fuel pump (FP) module contains the fuel pump, fuel pressure regulator and the fuel sender assembly. The fuel pressure regulator is attached to the fuel pump in the fuel pump module located in the fuel tank. It regulates fuel pressure supplied to the fuel injectors. The fuel pressure regulator is a diaphragm-operated relief valve. Fuel pressure is established by a spring preload applied to the diaphragm. Excess fuel is bypassed through the regulator and returned to the fuel tank.

Exhaust Gas Recirculation Systems
OverviewThe exhaust gas recirculation (EGR) system controls the oxides of nitrogen (NOx) emissions. Small amounts of exhaust gases are recirculated back into the combustion chamber to mix with the air/fuel charge. The combustion chamber temperature is reduced, lowering NOx emissions.Differential Pressure Feedback EGR (DPFE) System - OverviewThe DPFE system consists of a differential pressure feedback EGR sensor, EGR vacuum regulator solenoid, EGR valve, orifice tube assembly, powertrain control module (PCM) and connecting wires and vacuum hoses. Operation of the system is as follows:

1 The DPFE system receives signals from the ECT sensor or CHT sensor, IAT sensor, TP sensor, MAF sensor and CKP sensor to provide information on engine operating conditions to the PCM. The engine must be warm, stable and running at a moderate load and rpm before the EGR system is activated. The PCM deactivates EGR during idle, extended wide open throttle or whenever a failure is detected in an EGR component or EGR required input.
2 The PCM calculates the desired amount of EGR flow for a given engine condition. It then determines the desired pressure drop across the metering orifice required to achieve that flow and outputs the corresponding signal to the EGR vacuum regulator solenoid.
3 The EGR vacuum regulator solenoid receives a variable duty cycle signal (0 to 100%). The higher the duty cycle the more vacuum the solenoid diverts to the EGR valve
4 The increase in vacuum acting on the EGR valve diaphragm overcomes the valve spring and begins to lift the EGR valve pintle off its seat, causing exhaust gas to flow into the intake manifold.
5 Exhaust gas flowing through the EGR valve must first pass through the EGR metering orifice. With one side of the orifice exposed to exhaust backpressure and the other to the intake manifold, a pressure drop is created across the orifice whenever there is EGR flow. When the EGR valve closes, there is no longer flow across the metering orifice and pressure on both sides of the orifice is the same. The PCM constantly targets a desired pressure drop across the metering orifice to achieve the desired EGR flow.
6 The differential pressure feedback EGR sensor measures the actual pressure drop across the metering orifice and relays a proportional voltage signal (0 to 5 volts) to the PCM. The PCM uses this feedback signal to correct for any errors in achieving the desired EGR flow.Electric EGR System (EEGR) - OverviewThe EEGR system uses exhaust gas recirculation to control the oxides of nitrogen (NOx) emissions just like vacuum operated systems. The only difference is the way in which the exhaust gas is controlled.
The EEGR system consists of an electric motor/EGR valve integrated assembly, a PCM and connecting wiring. Additionally a MAP sensor is also required (2.3L engine only). Operation of the system is as follows:

1 The EEGR system receives signals from the ECT sensor or CHT sensor, TP sensor, MAF sensor, CKP sensor and the MAP sensor (2.3L) to provide information on engine operating conditions to the PCM. The engine must be warm, stable and running at a moderate load and rpm before the EEGR system is activated. The PCM will deactivate EEGR during idle, extended wide open throttle or whenever a failure is detected in an EEGR component or EGR required input.
2 The PCM calculates the desired amount of EGR for a given set of engine operating conditions.
3 The PCM in turn will output signals to the EEGR motor to move (advance or retract) a calibrated number of discrete steps. The electric stepper motor will directly actuate the EEGR valve, independent of engine vacuum. The EEGR valve is commanded from 0 to 52 discrete steps to get the EGR valve from a fully closed to fully open position. The position of the EGR valve determines the EGR flow.
4 (2.3L engine only) A MAP sensor is used to measure variations in manifold pressure as exhaust gas recirculation is introduced into the intake manifold. Variations in EGR being used will correlate to the MAP signal (increasing EGR will increase manifold pressure values).

Evaporative Emissions System Outline
OverviewThe evaporative emission (EVAP) system prevents fuel vapor build-up in the sealed fuel tank. Fuel vapors trapped in the sealed tank are vented through the vapor valve assembly on top of the tank. The vapors leave the valve assembly through a single vapor line and continue to the fuel vapor storage canister (located in the rear of vehicle along the frame rail) for storage until the vapors are purged to the engine for burning. The EVAP system uses the evaporative emission monitor to detect all leaks greater than 0.040 inch anywhere in the system.
The evaporative emission system monitor is a PCM on-board strategy designed to test the proper operation of the evaporative emissions system. The monitor tests the system components functions and the system's ability to flow fuel vapors (hydrocarbons) to the engine (intake manifold). DTCs associated with the evaporative emission system are P0442 and P0455.

Intake Air Systems

The intake air system provides clean air to the engine, optimizes air flow and reduces unwanted induction noise. The intake air system consists of an air cleaner assembly, resonator assemblies and hoses. The main component of the intake air system is the air cleaner assembly. The air cleaner assembly houses the air cleaner element that removes potential engine contaminants, particularly abrasive types. The MAF sensor is attached internally or externally to the air cleaner assembly and measures the quantity of air delivered to the engine combustion chamber. The MAF sensor can be serviced or replaced as an individual component. The intake air system also contains a sensor that measures the intake air temperature which may also be integrated with the MAF sensor. Air induction resonators are part of the intake air housing (i.e., conical air cleaner). The function of an air induction resonator is to reduce induction noise. The air induction components are connected to each other and to the throttle body assembly with hoses.

Positive Crankcase Ventilation System
OverviewThe positive crankcase ventilation (PCV) system cycles crankcase gases back through the engine where they are burned. The PCV valve regulates the amount of ventilating air and blow-by gas to the intake manifold and prevents backfire from traveling into the crankcase. The PCV valve should be mounted in a vertical position.

CAUTION:Do not remove the PCV system from the engine. Removal of the PCV system will adversely affect the fuel economy and engine ventilation and result in shorter engine life.

Catalyst and Exhaust Systems
OverviewThe catalytic converter and exhaust systems work together to control the release of harmful engine exhaust emissions into the atmosphere. The engine exhaust gas consists mainly of nitrogen (N), carbon dioxide (CO2) and water vapor (H2O). However, it also contains carbon monoxide (CO), oxides of nitrogen (NOx), hydrogen (H), and various unburned hydrocarbons (HCs). CO, NOx, and HCs are major air pollutants, and their emission into the atmosphere must be controlled.
The exhaust system consists of an exhaust manifold, front exhaust pipe, upstream heated oxygen sensor (HO2S), rear exhaust pipe, downstream HO2S, a muffler and an exhaust tailpipe. The catalytic converter is installed between the front and rear exhaust pipes. Catalytic converter efficiency is monitored by the OBD II system. See Engine OBD II Monitors.

Continued in Part 3 Part 3