EGR, PCV & Ignition Systems
EGR valve operation and NOx reduction, PCV system crankcase ventilation, ignition system types (COP/DIS), spark plug specifications, detonation, knock sensors, and variable valve timing.
- Explain the purpose of the EGR system and when EGR should be active
- Identify symptoms of a stuck-open EGR valve
- Describe the PCV system and effects of a stuck-closed PCV valve
- Compare COP and DIS ignition systems
- Explain detonation, knock sensors, and variable valve timing
Lección 1
EGR System & NOx Reduction
Purpose of the EGR System
The EGR (Exhaust Gas Recirculation) system reduces NOx emissions by lowering combustion temperatures. NOx (nitrogen oxides) forms when combustion temperatures exceed approximately 2,500 degrees F. By recirculating a small percentage of exhaust gas back into the intake, the EGR system dilutes the air-fuel mixture with inert gas, which absorbs heat and reduces peak combustion temperatures.
When EGR Should Be Active
EGR should be active during part-throttle cruise conditions, not at idle or WOT (wide open throttle). The ECM controls EGR flow based on engine operating conditions:
- Idle - EGR is OFF (would cause rough idle and stalling)
- Part-throttle cruise - EGR is ON (optimal conditions for NOx reduction)
- Wide open throttle (WOT) - EGR is OFF (maximum power needed)
- Cold engine - EGR is OFF (engine needs full combustion heat to warm up)
Stuck-Open EGR Valve Symptoms
A stuck-open EGR valve causes rough idle, stalling, hesitation because exhaust gas dilutes the mixture at idle when EGR should be off. The engine acts like it has a massive vacuum leak because inert exhaust gas displaces combustible air-fuel mixture.
Stuck Open EGR
Rough idle and stalling
Hesitation on acceleration
Low NOx emissions (too much dilution)
Possible misfire codes
Stuck Closed EGR
No idle issues
High NOx emissions
Spark knock/detonation under load
EGR flow insufficient code
The EGR system reduces NOx by lowering combustion temperatures. EGR should be active during part-throttle cruise only - not at idle or WOT. A stuck-open EGR valve causes rough idle, stalling, and hesitation.