Файл: 92FWD_25.pdf

HEATED INLET AIR SYSTEM

Turbo I, Turbo III, 3.0L, 3.3L and 3.8L engines do not use a heated inlet air system.

2.2L and 2.5L TBI air cleaners have a heated air assembly (Fig. 1). When ambient temperatures are low, the assembly warms the air before it enters the throttle body. The heated air assembly reduces hydrocarbon emissions, improves engine warm-up characteristics and minimizes icing.

Fig. 1 Heated Air Inlet System

The heated air assembly contains a vacuum operated blend door. The blend door opens to either heated air from a stove on the exhaust manifold or ambient air (outside air). A vacuum diaphragm operates the door. A spring opposes the vacuum diaphragm. A temperature sensor controls the vacuum diaphragm (Fig. 2). Adjustment of inlet air temperature occurs only at road load throttle positions or when the intake manifold vacuum exceeds the vacuum diaphragm spring rate.

Fig. 2 Heated Air Temperature Sensor

Air flows through the outside air inlet when ambient air temperature is 8°C (15°F) or more above the air temperature sensor control temperature.

When ambient air temperature falls below the control temperature, air flows through both the ambient and heated circuits. This occurs after the engine has been started and the exhaust manifold starts to give off heat. Colder ambient air cause greater air flow through the heat stove on the exhaust manifold. Warmer ambient air results in greater ambient air flow through the air cleaner snorkel.

HEATED INLET AIR SYSTEM SERVICE

Heated air inlet system malfunctions may affect driveability and vehicle exhaust emissions.

Use the following procedure to determine if the system functions properly.

(1)Inspect the condition of the heat stove to air cleaner flexible connector and all vacuum hoses. Inspect them for proper attachment. Replace as necessary.

(2)With a cold engine and ambient temperature less than 46°C (115°F.), the heat control door (valve plate) should be in the up (heat on position).

(3)With the engine warmed up and running, check the temperature of the air entering the snorkel or passing the sensor. When the temperature of the air entering the outer end of snorkel is 60°C (140°F.) or higher, the door should be in the down (heat off) position.

25 - 16 EMISSION CONTROL SYSTEMS

(4)Remove the air cleaner from the engine and allow it to cool down to 46°C (115°F). With 20 inches of vacuum applied to the sensor, the door should be in the up (heat on position). If the door does not rise to the heat on position, check the vacuum diaphragm for proper operation.

(5)To test the diaphragm, apply 20 inches of vacuum to it with vacuum pump tool number C-4207 or equivalent (Fig. 3). The diaphragm should not bleed down more than 10 inches of vacuum in 5 minutes. The door should not lift off the bottom of the snorkel at less than 2 inches of vacuum. The door should be in the full up position with no more than 4 inches of vacuum.

(6)If the vacuum diaphragm does not perform adequately, replace the heated air assembly.

Fig. 3 Testing Vacuum Diaphragm on Heated Air Inlet Systems

(7) If the vacuum diaphragm performs adequately but proper temperature is not maintained, replace the sensor and repeat the temperature checks in steps 2 and 3.

HEATED AIR TEMPERATURE SENSOR SERVICE

REMOVAL

(1)Remove air cleaner housing from vehicle.

(2)Disconnect vacuum hoses from air temperature sensor. Remove and discard retainer clips, new clips are supplied with a new sensor (Fig. 4).

(3)Remove and discard sensor and gasket.

INSTALLATION

(1)Position gasket on the sensor. Install sensor (Fig. 5).

(2)While supporting the sensor on outer diameter, install new retainer clips securely. Ensure the gasket compresses to form an air seal. Do not attempt to adjust the sensor.

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Fig. 4 Removing Sensor Clips

Fig. 5 Air Temperature Sensor Installation

HEATED OXYGEN SENSOR (O2 SENSOR)

The O2 sensor threads into the exhaust manifold. It provides an input v oltage to the engine controller. The input tells the engine controller the oxygen content of the exhaust gas (Fig. 6, 7, 8, 9, or 10). The engine controller uses this information to fine tune the air-fuel ratio by adjusting injector pulse width.

The O2 sensor produces voltages from 0 to 1 volt, depending upon the oxygen content of the exhaust gas in the exhaust manifold. When a large amount of oxygen is present (caused by a lean air-fuel mixture), the sensor produces a low voltage. When there is a lesser amount of oxygen present (rich air-fuel mixture), the sensor produces a higher voltage. By monitoring the oxygen content and converting it to electrical voltage, the sensor acts as a rich-lean switch.

The oxygen sensor contains a heating element that keeps it at proper temperature during all operating modes. Maintaining correct sensor temperature at all times allows the system to enter into closed loop operation sooner and remain in closed loop during periods of extended idle.

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Fig. 6 Oxygen SensorÐ2.5L Engine

Fig. 7 Oxygen SensorÐTurbo I Engine

In Closed Loop operation the engine controller monitors the O2 sensor input (along with other inputs) and adjusts the injector pulse width accordingly. During Open Loop operation the engine controller ignores the O2 sensor input. The controller adjusts injector pulse width based on preprogrammed (fixed) oxygen sensor input values and the current inputs from other sensors.

REMOVAL

CAUTION: Do not pull on the oxygen sensor wire when disconnecting the electrical connector.

EMISSION CONTROL SYSTEMS 25 - 17

Fig. 8 Oxygen SensorÐTurbo III Engine

Fig. 9 Oxygen SensorÐ3.0L Engine

Fig. 10 Oxygen SensorÐ3.3L/3.8L Engine

WARNING: THE EXHAUST MANIFOLD MAY BE EXTREMELY HOT. USE CARE WHEN SERVICING THE OXYGEN SENSOR.

(1) Disconnect oxygen sensor electrical connector.

(2) Remove sensor using Tool C-4907 (Fig. 11).

Fig. 11 Oxygen Sensor Socket

After removing the sensor, the exhaust manifold threads must be cleaned with an 18 mm X 1.5 + 6E tap. If reusing the original sensor, coat the sensor threads with an anti-seize compound such as Loctite 771-64 or equivalent. New sensors have compound on the threads and do not require additional compound. Tighten the sensor to 27 NIm (20 ft. lbs.) torque.

EXHAUST GAS RECIRCULATION (EGR) SYSTEM

Certain vehicles equipped with either a 2.2L, 2.5L, 3.0L, 3.3L or 3.8L engines may use a backpressure type Exhaust Gas Recirculation (EGR) system (Fig. 12, 13, or 14). Turbo I and Turbo III engines do not use an EGR system.

The EGR system reduces oxides of nitrogen (NOx) in engine exhaust and helps prevent spark knock. The system allows a predetermined amount of hot exhaust gas to recirculate and dilute the incoming air/fuel mixture. The diluted air/fuel mixture reduces peak flame temperature during combustion.

The EGR system consists of:

²EGR tube (connects a passage in the intake manifold to the exhaust manifold)

²EGR valve

²Electronic EGR Transducer (EET)

²Connecting hoses

The electronic EGR transducer (EET) contains an electrically operated solenoid and a back-pressure transducer (Fig. 15). The engine controller operates the solenoid. The controller determines when to energize the solenoid. Exhaust system back-pressure controls the transducer.

When the controller energizes the solenoid, vacuum does not reach the transducer. Vacuum flows to the transducer when the controller de-energizes the solenoid.

When exhaust system back-pressure becomes high enough, it fully closes a bleed valve in the transducer. When the controller de-energizes the solenoid and back-pressure closes the transducer bleed valve, vacuum flows through the transducer to operate the EGR valve.

De-energizing the solenoid, but not fully closing the transducer bleed hole (because of by low back-

Fig. 12 EGR SystemÐ2.2L and 2.5L TBI Engines

Fig. 13 EGR SystemÐ3.0L Engines

pressure), varies the strength of vacuum applied to the EGR valve. Varying the strength of the vacuum changes the amount of EGR supplied to the engine. This provides the correct amount of exhaust gas recirculation for different operating conditions.

These systems do not allow EGR at idle. The 2.2L/2.5L EGR systems operate at all temperatures. The 3.0L, 3.3L and 3.8L EGR systems do not operate when coolant temperature is below 4.5°C (40°)F at start-up. These systems activate when coolant temperature reaches 77°C (170°F).

Fig. 14 EGR MountingÐ3.3L and 3.8L Engines

Fig. 15 Electric EGR Transducer (EET) Assembly

EGR SYSTEM ON-BOARD DIAGNOSTICS (CALIFORNIA VEHICLES)

The engine controller performs an on-board diagnostic check of the EGR system on all California vehicles with EGR systems. The diagnostic system uses the Electric EGR Transducer (EET) for the system tests.

The diagnostic check activates only during selected engine/driving conditions. When the conditions are met, the engine controller energizes the transducer solenoid to disable the EGR. The controller checks for a change in the oxygen sensor signal. If the air-fuel mixture goes lean, the engine controller will attempt to enrichen the mixture. The engine controller registers a fault if the EGR system has failed or degraded. After registering a fault, the engine controller turns

the Check Engine light on. The Check Engine light indicates the need for immediate service.

If a malfunction is indicated by the Check Engine light and a fault code for the EGR system, check for proper operation of the EGR system. Use the System Test, EGR Gas Flow Test and EGR Diagnosis Chart. If the EGR system tests properly, check the system using the DRB II tester. Refer to On-Board Diagnosis in the General Diagnosis sections of Group 14. Also, refer to the DRB II and the appropriate Powertrain Diagnostics Procedure manual.

EXHAUST GAS RECIRCULATION (EGR) SYSTEM TEST

WARNING: APPLY PARKING BRAKE AND/OR BLOCK WHEELS BEFORE PERFORMING EGR SYSTEM TEST.

A failed or malfunctioning EGR system can cause engine spark knock, sags or hesitation, rough idle, and/or engine stalling. To ensure proper operation of the EGR system, all passages and moving parts must be free of deposits that could cause plugging or sticking. Ensure system hoses do not leak. Replace leaking components.

Inspect hose connections between the throttle body, intake manifold, EGR solenoid and transducer, and EGR valve. Replace hardened, cracked, or melted hoses. Repair or replace faulty connectors.

Check the EGR control system and EGR valve with the engine fully warmed up and running (engine coolant temperature over 150°F). With the transmission in neutral and the throttle closed, allow the engine to idle for 70 seconds. Abruptly accelerate the engine to approximately 2000 rpm, but not over 3000 rpm. The EGR valve stem should move when accelerating the engine (the relative position of the groove on the EGR valve stem should change). Repeat the test several times to confirm movement. If the EGR valve stem moves, the control system is operating normally. If the control system is not operating normally, refer to the EGR Diagnosis Chart to determine the cause.

EGR GAS FLOW TEST

The following procedure should be used to determine if exhaust gas is flowing through the EGR system.

Connect a hand vacuum pump to the EGR valve vacuum motor. With engine running at idle speed, slowly apply vacuum. Engine speed should begin to drop when applied vacuum reaches 2.0 to 3.5 inches. Engine speed may drop quickly or engine may even stall. This indicates that EGR gas is flowing through the system.