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Emission Devices

Learn about PCV, Evap, and EGR systems in vehicles, their components, operation, and common problems. Discover how these systems control emissions for better engine performance and environmental impact.

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Emission Devices

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  1. Emission Devices

  2. PCV systems

  3. Purpose of PCV • Control of blowbye gasses (HC) • Reducing moisture and acids extending oil life

  4. Components of PCV • Breather to filter incoming air • PCV valve • Calibrated vacuum leak to intake manifold • Controls flow rates based on strength of vacuum • Eliminates backfiring path to crankcase • Bleed orifice type / dual bleed type

  5. PCV system problems • Can flow up to 20% of the total a/f mixture at idle • Plugged system could cause high CO at idle • Stuck open valve could cause lean or high idle speed

  6. Evaporative emissions system

  7. Evap system purpose • To control HC during fuel evaporation

  8. Evap system components • Gas cap • Important seal of system • Easily over looked • Allows air in but pressure out only if >1 psi • Vapor liquid separator

  9. Evap system components • Canister • Stores evaporating vapors • Approx. 1.5 Lbs. Activated charcoal • Can hold twice it’s own weight in fuel • Chrysler used the crankcase in 1971 • Vapor line(s) from tank(s)

  10. Evap system operation (purging) • Typical operation • None at idle • May use ported vacuum for purging • May have manifold vacuum purge but be controlled by ported • Needs TVS to eliminate cold operation • Computer controls common • OBDII must have diagnostics for system

  11. EGR systems

  12. Purpose : flows exhaust gas into intake to lower combustion temps which lowers NOx

  13. EGR details • Exhaust supports no combustion • Dilutes a/f mix and slows combustion slightly • First used on Buicks in 1972, common in 1973 • Does not affect a/f ratios

  14. Control of EGR needed for three reasons • Idle; can not support dilution and little NOx • Cold; poor driveability, no NOx, not all engines • WOT; limits power and less NOx due to richer a/f

  15. EGR valve is a means of controlling EGR flow • Basic systems use ported vacuum to control and limit operation and a TVS to eliminate cold operation

  16. Electronic controls • Can use vsv’s to control EGR via ECU • Electric valves • Using solenoids to control operation • Sensors • Position (EVP) • Exhaust pressure (PFE) • Temperature switch

  17. Problems • Inop valves cause high combustion temps = pinging =NOx • Plugged EGR passages common • Too much EGR = lack of power, surge • Stuck open at idle causes rough idle due to excessive dilution

  18. END ------------ OF IT ALL

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