Presentation on theme: "Exhaust Gas Recirculation (EGR)"— Presentation transcript:
1 Exhaust Gas Recirculation (EGR) Lowers Oxides of Nitrogen (NOx) emissions caused by high combustion tempsReduces engine knock (ping)EGR decreases combustion temperaturesEGR valve = main element of EGR systemFeeds small amounts of exhaust back to the combustion chamberThis dilutes the air/fuel mixture, combustion temperatures are reducedValve is open during engine cruise periodsEGR activation:Warm engine operationAbove idle speedEGR flow calculationPCM looks at readings from:ECTTPSVSSMAP or MAFIGN REFEGR 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.SpringPintlePassagesEGR 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 engineOpens 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 systemsBasic standard since 1973.
4 Types of EGR: Integral Backpressure With or without PCM Internal Modulator controls EGR flow based on positive or negative exhaust pulsesThicker 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 pressureVacuum 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 PCMMay 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 inappropriatelySensor may be called EVP, or Lift sensorEGR SOLENOID
7 Types of EGR: Linear Solenoid EGR No vacuum control PCM PWM Improved accuracyFaster response (10X)Improved diagnosticsMay use MAP or “Integrator” to verify EGR gas is flowingScan tool provides functional test.
8 Types of EGR:Linear EGR schematic5 wire:2 for solenoid3 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 flowingScan tool provides functional test.
11 Types of EGR: GM Integrated Electronic Combines vacuum and electronic operationPCM 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 backpressureLow backpressureWhen 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 solenoidPCM command opens or closes vacuum solenoidModulator controls EGR flow based on vacuum & exhaust backpressureVacuum signal varies through throttle opening