EGR System Cadillac Brougham I

DESCRIPTION

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

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

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 part number. Letter "P" designates a positive backpressure valve and letter "N" a negative backpressure valve.

Some 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, base temperature will be cool. Temperature sensor will then signal ECM to turn on "SERVICE ENGINE SOON" (SES) 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 EGR diaphragm chamber by bleeding vacuum to atmosphere during certain operating conditions.

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

Scheme 23

Negative Backpressure EGR Valve

Vacuum is applied to upper EGR diaphragm via a hose connected intake manifold vacuum. Manifold vacuum is also applied to lower EGR diaphragm (through intake port at base of EGR valve). (Scheme 24)

When manifold vacuum in lower chamber is insufficient to overcome spring tension on lower diaphragm, bleed valve will be closed, allowing vacuum in upper chamber to open EGR valve. With engine at idle, or under light load, high manifold vacuum applied to lower chamber opens air bleed valve in lower diaphragm. This bleeds off vacuum in upper chamber, keeping the EGR valve closed.

Scheme 24

The Electronic Control Module (ECM) controls EGR valve operation. The ECM uses information from input sensors to determine correct amount of EGR. (Scheme 25)

This type EGR system is controlled entirely by the ECM. The ECM controls the flow rate by controlling an electrical signal to a solenoid vacuum valve. The ECM controlled vacuum solenoid valve is located in series between vacuum source and EGR valve. 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.

Scheme 25

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.

Scheme 26

The digital EGR valve is designed to accurately supply EGR to engine, independent of intake manifold vacuum. The valve controls EGR flow from exhaust to 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 to open the orifice.

Scheme 27

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.

Scheme 28

EGR VACUUM SOLENOID

1. Disconnect electrical connector at solenoid. Turn ignition on. Using a test light, ensure voltage is present at connector. Turn ignition off. Using an ohmmeter, check resistance across solenoid terminals. Resistance should be at least 20 ohms, but not infinity.
2. Disconnect vacuum source hose at solenoid. Using a vacuum gauge connected to source hose, check that a minimum of 10 in. Hg. vacuum is present with engine running. For further testing of EGR vacuum solenoid, see appropriate C-7 CHART in the COMPUTERIZED ENGINE CONTROLS section.

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 is 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, remove EGR valve. 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 to hose connected to EGR valve seat. The EGR valve should close immediately.

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. If engine RPM does not drop, clean EGR valve and passages.
2. Check for EGR valve diaphragm movement with engine RPM change from 2000 RPM to idle. EGR valve diaphragm should not change. If EGR valve diaphragm moves with RPM change, check Park/Neutral switch for open circuit or misadjustment. If EGR valve diaphragm does not move, disconnect ALDL "test" connector and ground test terminal. If EGR valve diaphragm moves, EGR valve is functioning properly.
3. 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 ALDL "test" terminal. Test light should flash repeatedly.
4. 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.
5. 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. See appropriate C-7 CHART in the COMPUTERIZED ENGINE CONTROLS section for further diagnosis.

INTEGRATED ELECTRONIC EGR VALVE

1. With ignition off, connect vacuum gauge to EGR valve. Apply vacuum and observe EGR valve. EGR valve should not move. If valve moves, check that vent filter is unrestricted and replace EGR valve (if necessary).
2. Turn ignition on and repeat Step 1). When applying vacuum, EGR valve should not move. If EGR valve moves, a fault exists in ECM or electrical circuits. See appropriate C-7 CHART in the COMPUTERIZED ENGINE CONTROLS section for further diagnosis.

DIGITAL EGR VALVE

See appropriate CHART in the COMPUTERIZED ENGINE CONTROLS section.