Why Does My Porsche Cayenne's Exhaust Sound So Loud
VVC AUTO 85.5 - Smog Technician - Level 1 - Nox
1. Module I
Module goals
How NOx is created
How temperature affects NOx
How compression affects NOx
How EGR affects NOx
How A/F ratios affect NOx
Post combustion controls to reduce NOx
How cats reduce NOx
2. Vehicle emissions have been controlled since
PCV systems were introduced in 1961
Early exhaust diagnosis was done using CO &
HC
Later 02 & C02 was used
3. NOx was associated as a key player in the
production of photo chemical smog in the late
60’s
Efforts to reduce CO & HC caused NOx to
increase
Module 1 addresses NOx
Formation
Control
4. The internal combustion engine is a large air
pump
Oxygen = 20% = small amount of what is
drawn into the engine
Nitrogen = 80% = Large amount of what is
drawn into engine
Plus a very small amount of inert gas
As an engine wears NOx forms
5. Two ways to control NOx
Precombustion
Before combustion
Post-combustion
After combustion
6. Precombustion controls
Keeps combustion chamber temperatures below 2500
degrees Fahrenheit
Lower compression ratios
Less compression = less heat
Richer A/F ratios
More fuel = less heat
When A/F ratio reaches 16:1 NOx decreases (lean misfire)
EGR systems lowers combustion temperature.
Computer Programming
Retarded timing
Richer A/F ratios
7. Post-combustion controls
After combustion
Three way Catalytic Converters
Catalytic Converters are a secondary method
only – they will not overcome excess NOx
created by the engine.
8. Ignition timing
Initial & total
EGR system
Must pass functional test
Fuel octane
Low burns too fast and tends to explode!
Air intake temperature
Air duct or cooling systems problems
Carbon buildup
Increases compression
Hot spots
Air pump operation
Must divert
Dirty fuel injectors
Restricted or bad pattern
Lean engine operation
Lean = heat, lean fuel mixture burn too slow!
9. Other early precombustion systems
Spark control -- controls timing advance
TAC -- preheats intake air when cold
EGR -- recirculates exhaust gasses to lower
combustion chamber temperatures
EFE -- heats intake manifold
10. Combustion chamber carbon treatment
Run additive through engine to burn off carbon
NOx diagnosis = think what will cause heat