1. Exhaust Gas Recirculation (EGR)
Lowers Oxides of Nitrogen (NOx) emissions caused by high combustion temps
Reduces engine knock (ping)
EGR decreases combustion temperatures
EGR valve = main element of EGR system
Feeds small amounts of exhaust back to the combustion chamber
This dilutes the air/fuel mixture, combustion temperatures are reduced
Valve is open during engine cruise periods
EGR activation:
Warm engine operation
Above idle speed
EGR flow calculation
PCM looks at readings from:
ECT
TPS
VSS
MAP or MAF
IGN REF
EGR is deactivated during:
Coolant temperature below about 57ºC (134ºF).
During deceleration (throttle valve closed).
Light engine load (amount of intake air very small).
Engine speed approximately 4000 RPM or more.
Engine racing (neutral start switch turned on).
Some systems prevent EGR until Trans in “gear”
Some systems prevent EGR until VSS is present.

2. Spring Pintle Passages
The EGR valve opens and closes the passage between the exhaust manifold and intake manifold. Vacuum is used to move the EGR valves.
Spring
Pintle
Passages
EGR opens and closes a passage between exhaust and intake.
EGR valves are opened using:
Vacuum (usually ported, may use vacuum control solenoid)
Electronic (EGR valve uses solenoid)

3. Types of EGR: Single Diaphragm Used with or without PCM controls
When the engine is idling, opening valve should stall the engine
Opens fully with about 8” Hg.
Used with a thermal vacuum switch and a possible vacuum delay valve.
Single diaphragm may be used in an electronically controlled systems
Basic standard since 1973 .

4. Types of EGR: Integral Backpressure With or without PCM
Internal Modulator controls EGR flow based on positive or negative exhaust pulses
Thicker pintle shaft is hollow to allow exhaust pressure into the valve.
The exhaust pulses vary a EGR vacuum using a built-in control valve (modulator).
When exhaust pressure or vacuum is present, EGR will open.
Without exhaust pulses (neg or positive) , the EGR valve will not hold vacuum.
As engine load increases, so do exhaust pulses, this causes the EGR to open.
To test a positive pressure valve, rev engine to 2,000 rpms to create back pressure, apply vacuum.
To test a negative pressure valve, apply vacuum with engine off (should open)
EGR should open and cause a 100 rpm drop or more.
Exhaust mods (headers) can change pressure and set DTCs.

5. Types of EGR: External Modulator With or without PCM
External Modulator controls EGR flow based exhaust pressure
Vacuum modulation is vital for good driveability and precise NOx control.

6. Types of EGR: External sensor PCM commands solenoid (VSV)
Sensor reports EGR valve position to PCM
May use 2 solenoids (vacuum and vent)
Sensor is a linear potentiometer (3 wire)
Carbon buildup raises pintle and sets DTCs (common!)
Solenoids may stick and apply vacuum inappropriately
Sensor may be called EVP, or Lift sensor
EGR SOLENOID

7. Types of EGR: Linear Solenoid EGR No vacuum control PCM PWM
Improved accuracy
Faster response (10X)
Improved diagnostics
May use MAP or “Integrator” to verify EGR gas is flowing
Scan tool provides functional test.

8. Types of EGR:
Linear EGR schematic
5 wire:
2 for solenoid
3 for sensor

9. Types of EGR: GM digital No vacuum
3 solenoids, 3 different exhaust ports.
Valves may be operated separately or together to control EGR.
May use MAP or “Integrator” to verify EGR gas is flowing
Scan tool provides functional test.

10. Types of EGR:
GM Digital Schematic

11. Types of EGR: GM Integrated Electronic
Combines vacuum and electronic operation
PCM controlled vacuum regulator is built into the top of the EGR valve.
PWM signals operate regulator solenoid and control vacuum.
Ported vacuum is supplied to the EGR valve assembly.
EGR pintle sensor provides feedback to the PCM to verify desired action has occurred.

12. Types of EGR: GM EGR solenoid details. PCM controlled PWM
PCM regulates the time the EGR is open by regulating solenoid on time (more EGR).
Percentage of solenoid on time is the duty cycle:
0% equals no EGR; 100% equals maximum EGR.
EGR vacuum switch signals PCM -vacuum present

13. External Modulator with PCM controlled vacuum solenoid
High backpressure
Low backpressure
When EGR is not needed and to maintain driveability the EGR can be disabled.
Non PCM systems use controls such as a temperature vacuum switch.
PCM controlled EGR use solenoids for precise control.
Typically EGR is disabled when the following conditions exist:
Coolant temperature below 57ºC (134ºF).
During deceleration (throttle valve closed).
Light engine load (amount of intake air very small).
Engine speed approximately 4000 RPM or more.
Engine racing (neutral start switch turned on).
External Modulator with PCM controlled vacuum solenoid
PCM command opens or closes vacuum solenoid
Modulator controls EGR flow based on vacuum & exhaust backpressure
Vacuum signal varies through throttle opening

14. Various EGR controls