EGR System Chevrolet Camaro III рестайлинг

DESCRIPTION

The Exhaust Gas Recirculation (EGR) system, is designed to reduce oxides of nitrogen (NOx) emissions. This process is accomplished by lowering combustion temperatures of burning gases. A metered amount of exhaust gas is recirculated into the intake manifold and mixed with the air/fuel mixture.

On some models, the Electronic Control Module (ECM) controls EGR valve operation by controlling vacuum to EGR valve. An ECM controlled vacuum solenoid valve is located in series between vacuum source and EGR valve. The ECM uses information from input sensors to determine the correct amount of EGR.

A Thermal Vacuum Valve (TVV), Thermal Vacuum Switch (TVS) or an electrically operated solenoid controls operating vacuum, depending on engine operating temperature, to maintain good cold driveability.

There are 5 types of EGR systems used, pulse width modulated, electronic, ported, digital and backpressure (positive and negative) systems.

Cutaway View of Positive Backpressure EGR Valve. Scheme 53

In this system the amount of exhaust gas entering the intake manifold depends on a vacuum signal (ported vacuum), controlled by throttle position.

When the throttle is closed (at idle or deceleration), there is no vacuum signal to EGR valve because the EGR vacuum port is above the closed throttle valve. As the throttle valve is opened, a ported vacuum signal is supplied to the EGR valve, admitting exhaust gas into the intake manifold.

View of Ported & Pulse Width Modulated EGR Valve. Scheme 54

Two types of backpressure EGR valves are used, a positive or negative backpressure valve. These valves may be identified by the letter in the last position of the part number. Letter "P" designates a positive backpressure valve and letter "N" a negative backpressure valve.

Some 4.3L V6, 5.0L and 5.7L V8 models have backpressure EGR valves with a temperature sensor built into valve base.

On these models, ECM monitors EGR valve base temperature. If EGR valve does not open properly, base temperature will be cool. Temperature sensor will then signal ECM to turn on check engine light.

Positive Backpressure EGR Valve

A control valve, located in the EGR valve, acts as a vacuum regulator valve. The control valve regulates the amount of vacuum to the EGR diaphragm chamber by bleeding vacuum to the atmosphere during certain operating conditions.

When the control valve receives a backpressure signal, through the hollow shaft of the EGR valve, pressure on the bottom of the control valve closes the control valve. When the control valve closes, the maximum vacuum signal is applied directly to the EGR valve allowing exhaust gas recirculation.

Negative Backpressure EGR Valve

If there is little or no vacuum in the vacuum chamber of the EGR valve, the EGR valve will not open. When there is enough vacuum in the chamber from the manifold vacuum port, the pintle will rise off its seat and allow the EGR valve to open.

When the EGR valve opens, backpressure in the hollow shaft decreases. As backpressure decreases, vacuum opens the control valve and bleeds EGR control vacuum to the atmosphere, closing the EGR valve.

Cutaway View of Negative Backpressure EGR Valve. Scheme 55

This type EGR system is controlled entirely by the ECM. The ECM controls the flow rate through a solenoid. The solenoid is pulsed at a rate of up to 32 times per second. The ECM uses a ported vacuum signal to determine the flow rate signal to the solenoid.

The integrated electronic EGR valve functions similar to a ported EGR valve with a remote vacuum regulator. The internal solenoid is normally open, which causes the vacuum signal to be vented off to the atmosphere when EGR is not controlled by the ECM.

This EGR valve has a sealed cap. The solenoid valve opens and closes the vacuum signal, which controls the amount of vacuum vented to atmosphere. This controls the amount of vacuum applied to the diaphragm.

The electronic EGR valve contains a voltage regulator, which converts ECM signal and regulates current to the solenoid. The ECM controls EGR flow with a pulse width modulated signal based on airflow, Throttle Position Sensor (TPS), and RPM. This system also contains a pintle position sensor, which works similar to a TPS sensor. As EGR flow is increased, the sensor output increases.

Cutaway View of Integrated Electronic EGR Valve. Scheme 56

The digital EGR valve is designed to accurately supply EGR to the engine, independent of intake manifold vacuum. The valve controls EGR flow from the exhaust to the intake manifold through 3 orifices, to produce 7 different combinations. When a solenoid is energized, the armature, with attached shaft and swivel pintle is lifted, opening the orifice.

Digital EGR Valve. Scheme 57

EGR VALVE CLEANING

One-Piece Valve

1. Remove EGR valve and discard gasket. Lightly tap sides and end of valve. Shake valve to remove any loose deposits. Buff exhaust deposits from mounting surface with a wire wheel. Visually inspect valve seating area to ensure that surface is clean.
2. Inspect for exhaust deposits in valve outlet. Carefully remove any deposits with a screwdriver. Using a new gasket, reinstall EGR valve.

3.0L & 3.8L V6 Only

Replace EGR solenoid filter every 30,000 miles. When installing filter, ensure that solenoid wires are aligned in cut-out section of filter. (Scheme 58)

Replacing EGR Solenoid Filter (3.0L & 3.8L). Scheme 58

EGR CONTROL CIRCUIT

For testing of EGR control circuit, see appropriate diagnostic chart in COMPUTER COMMAND CONTROL article.

COMPONENT TESTING

PULSE WIDTH MODULATED EGR VALVE

1. Check vacuum lines for leaks and electrical connectors for proper installation. Place transmission in "Park" or "Neutral". With engine at normal operating temperature and engine idling, push up on underside of EGR valve diaphragm. Engine RPM should drop.
2. If engine RPM does not drop, clean EGR valve or passages. If RPM still does not drop, replace EGR valve. If engine RPM does drop, check for EGR valve diaphragm movement with idle speed change from 2000 RPM to idle. EGR valve diaphragm should not change.
3. If EGR valve diaphragm moves with idle change, check Park/Neutral switch for open circuit or misadjustment of switch. If EGR valve diaphragm does not move, disconnect EST connector and ground test terminal. If EGR valve diaphragm moves, EGR valve is functioning properly.
4. If EGR valve diaphragm still does not move, stop engine and disconnect EGR solenoid connector. Connect 12-volt test light between EGR solenoid connector terminals. Turn ignition on and ground test terminal. Test light should flash repeatedly.
5. If test light flashes, check for vacuum to EGR solenoid at 2000-3000 RPM. If engine does not use a vacuum regulator, there should be at least 7 in. Hg vacuum at solenoid. If engine is equipped with a vacuum regulator, there should be 2-10 in. Hg vacuum.
6. If vacuum is greater than 10 in. Hg, replace regulator. If vacuum is less than 2 in. Hg, vacuum at solenoid is okay and check EGR solenoid connections and/or faulty EGR solenoid.
7. If test light was on steady, check for ground in wire to ECM terminal "T". If terminal is not grounded, check for faulty ECM. If test light is off, connect test light from each EGR connector terminal to ground and note light.
8. If test light is on at both terminals, check for short to battery positive in wire to ECM terminal "T". Repair and recheck as required, ECM may be damaged.
9. If test light is off, repair open in wire from solenoid to ignition. Check for blown fuse. If test light is on only at one terminal, check for open in wire to ECM terminal "T". If wire is not open, check resistance of EGR solenoid.
10. Resistance should be over 20 ohms. If resistance is below 20 ohms, replace EGR solenoid and ECM. If resistance is over 20 ohms, ECM or connections may be faulty. If further testing is required, see appropriate diagnostic chart in COMPUTER COMMAND CONTROL article.

INTEGRATED ELECTRONIC EGR VALVE

1. Turn ignition off. Connect vacuum gauge to EGR valve. Apply vacuum and observe EGR valve. EGR valve should not move. If EGR valve moves, remove EGR filter and repeat test. EGR valve should not move. If valve moves, replace EGR valve. If valve does not move, replace filter.
2. When applying vacuum, if EGR valve does not move, turn ignition on and repeat test. EGR valve should not move. If EGR valve moves, disconnect electrical connector.
3. Connect 12-volt test light between terminals "A" and "D". Test light should not light. If test light does not light, EGR valve is faulty. If test light does light, circuit 435 is shorted to ground or ECM is faulty.
4. With ignition on, ground diagnostic test terminal and repeat test. Valve should move. If valve does not move, remove EGR electrical connector. Connect test light between terminals "A" and "D".
5. Test light should light. If test light does light, EGR valve or connection is faulty. If test light does not light, probe terminal "D" with test light to ground. Test light should light.
6. If test light does light, circuit 435 or ECM is faulty. If test light did not light, circuit 39 is open. When diagnostic terminal was grounded, see if EGR valve moved. If so, disconnect vacuum hose at valve and connect vacuum gauge to hose.
7. EGR valve should be able to obtain and hold 3-7 in. Hg vacuum. If valve holds vacuum above 7 in. Hg, remove EGR filter and repeat test. If vacuum is above 7 in. Hg, replace EGR valve. If vacuum was 3-7 in. Hg, replace EGR filter.
8. If EGR valve is holding 3-7 in. Hg vacuum, start engine and lift EGR diaphragm. Idle should become rough. If idle does not become rough, remove EGR valve and clean passages. If idle did become rough, EGR valve is okay.
9. Check for ported vacuum to EGR valve and check for leaks or restrictions in vacuum hoses. There should be at least 7 in. Hg vacuum at 2000 RPM. If further testing is required, see appropriate diagnostic chart in COMPUTER COMMAND CONTROL article.

PORT EGR VALVE

1. Turn ignition off. Disconnect vacuum hose at vacuum signal tube of EGR valve. Connect a vacuum pump to vacuum signal tube and apply 10 in. Hg vacuum. EGR diaphragm plate should move up and remain up for at least 20 seconds.
2. If diaphragm moves up and holds for 20 seconds, diaphragm is operating properly. If diaphragm does not hold vacuum, replace EGR valve. Place transmission in "PARK" or "NEUTRAL" and connect vacuum pump to EGR valve.
3. With engine running at normal operating temperature, push up on diaphragm. Engine RPM should decrease. If RPM decreases, EGR valve is functioning properly. If engine RPM does not decrease, replace EGR valve. If further testing is required, see appropriate diagnostic chart in COMPUTER COMMAND CONTROL article.

DIGITAL EGR VALVE

1. Turn engine off. Disconnect EGR connector. Using Tool Kit (J-35616), install jumper harness connector terminal "D" to terminal "D" of EGR valve. Connect jumper to ground. Start engine. Engine RPM should change as each EGR valve terminal "A", "B" or "C" is contacted. For terminal location, see appropriate diagnostic chart in COMPUTER COMMAND CONTROL article.
2. If engine RPM does not change, check for restriction in EGR supply tube or plugged EGR orifice. If EGR valve is not restricted or plugged, replace EGR valve. If engine RPM does change, digital EGR valve is functioning properly. If further testing is required, see appropriate diagnostic chart in COMPUTER COMMAND CONTROL article.

1. Place transmission in "PARK" or "NEUTRAL". Set parking brake and block drive wheels. Connect tachometer. With engine running at normal operating temperature, ensure fast idle speed set to specifications.
2. Run engine at 2000 RPM. On carbureted engines, place fast idle cam on high step. Disconnect vacuum hose from EGR valve and plug hose. EGR valve diaphragm should move down and engine RPM should increase. NOTE: On some engines with ECM controlled solenoid, the EGR vacuum is locked out in Park/Neutral and solenoid must be by-passed.
3. Reconnect vacuum hose. Diaphragm should move up and engine RPM should decrease. A slight vibration of diaphragm plate may be noticed in backpressure EGR valves.
4. If engine RPM did change and EGR diaphragm moved, the EGR valve is functioning properly. If engine RPM did not change and diaphragm did not move, remove EGR valve and apply 10 in. Hg vacuum to EGR vacuum signal tube. EGR valve should not open.
5. If EGR valve opens, replace EGR valve. With vacuum still applied, direct a stream or air (15 psi maximum) into valve seat. EGR valve should open completely.
6. If air is not available, connect a section of hose over EGR valve seat. Connect a vacuum pump to signal tube. With thumb plugging intake port of EGR valve, operate vacuum pump while alternately blowing and pausing.
7. With vacuum present at signal tube, EGR valve should open while pressure is applied and should close when no vacuum is present.

1. With EGR valve in vehicle and engine off, disconnect EGR valve vacuum signal hose. Connect vacuum pump to vacuum signal tube and apply 10 in. Hg vacuum. EGR diaphragm should move up and remain up for 20 seconds.
2. If diaphragm does not stay up for 20 seconds, replace EGR valve. Using an assistant, again apply 10 in. Hg vacuum to signal tube. Have assistant immediately try to start engine. Observe diaphragm for movement.
3. If diaphragm moves to a seated position (valve closed) during cranking and initial starting, EGR valve is functioning properly. If diaphragm did not move, clean or replace EGR valve.
4. If EGR valve is not in vehicle, connect a short section of hose over the EGR valve seat. Apply 10 in. Hg vacuum to vacuum signal tube. EGR valve should open. If valve does not open, clean or replace EGR valve.
5. With vacuum still applied, plug intake port of valve with thumb. Apply suction (with mouth) to hose connected to EGR valve seat. The EGR valve should close immediately.