Emissions
Dec 21, 2015
Emissions
Air is made up of :
21%O2 78%N 1% other gasses (mostly argon)
Fuel is primarily made up of :
Hydrocarbons (HC)
Perfect combustion
HC, O2, N2 in Heat, H2O, CO2 and N2 out
Imperfect combustion
Adds HC, CO, NOx and O2 to exhaust
Stoichiometric
Much of our emissions are related directly to A/F mixtures
Theoretical best A/F ratio for emissions, economy, performance is 14.7:1
14.7 pounds of air to 1 pound of fuel
Think about it
Gasoline weighs 6 pounds per gallon Air weighs 1 pound per 100 gallons At 15:1 it takes 9000 gallons of air to
burn 1 gallon of fuel– 9000 Gallons of air is equal to a single car
garage
HC - Hydrocarbons
Unburned fuel Currently measured in parts per million
(ppm)
Common causes of high HC
Missfiring will cause HCs– Ignition – Mechanical – Lean
A/f ratios off either way Timing too advanced
– Cools exhaust and cylinder walls
Not so common causes of HC
Quench areas in combustion chamber– Carbon – Poor combustion chamber design
Cam profiles too aggressive
CO - Carbon monoxide
Currently measured in % EXTREMELY deadly gas!!! Partially burned fuel Too much fuel or too little O2
– Combustion process ran out of air CO directly related to a/f ratios
Causes of high CO
Any thing that will cause a rich fuel mixture– Sensor malfunction– Carburetor or injector failures– Diluted oil
Hard to use as an A/F guide over 15:1 due to flattening out of curve– Must use O2 above stoichiometric
O2 - Oxygen
Currently measured in % Unused air in exhaust O2 directly related to A/F Can also come from dilution
– Air pump, exhaust leaks Missfires will raise O2 If O2 is > 5% and vehicle running OK then it
must be from dilution
CO2 - Carbon dioxide
Currently measured in % Byproduct of complete combustion Peak indicates good A/F Any problems pull CO2 away from peak Used by Washington State to determine
exhaust system integrity
NOx - Oxides of nitrogen
Created when peak combustion temps. exceed 2500F
Causes of high NOx
Advanced timing Inoperative EGR Carbon build up Anything that overheats combustion
chamber
Smog, what is it?
Ground level ozone - O3 Three ingredients; HC, NOx and
sunlight CO is a pollutant all by itself
State emissions testing
Attainment areas vs. non-attainment areas– Ozone and/or CO
Centralized vs. non-centralized testing
ASM test
Loaded test with constant load with a CVS
Idle test With or without an evaporative
emissions test Test all three gasses
Washington State test
Variation of a ASM test Loaded cruise test except special
vehicles Idle test No NOx measuring in effect yet
IM240 test
Varying load test with a constant volume sampler
Idle test Evaporative emissions test Testing all three gases Visual inspection
Remote sensing devices
Like photo radar Used in California / Colorado
Emission Controls
PCV systems
Purpose of PCV
Control of blowbye gasses (HC) Reducing moisture and acids extending
oil life
PCV history
Road draft tube was responsible for 20-25% of vehicles emissions
Completely sealed systems on all domestics since 1968
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
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
PCV system diagnosis / testing
Valve should snap back at idle Rattle test Cheap valves pass both tests but could
flow wrong Inspect breathers for plugging Oil dilution
– 1% Change = too much dilution or blowbye
Inspect / replace at tune up intervals
Evaporative emissions system
Evap system purpose To control HC during fuel evaporation
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
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) Carb bowl venting
– Electronic solenoids
– Switching with purge valve
Evap system operation (purging)
Uses stored fuel vapors in canister Variable type-hose to air cleaner
snorkel Constant purge type-vacuum to
manifold– Uses TVS and orifice
Evap system operation (purging)
Demand system– None at idle– Uses ported vacuum as control– Manifold vacuum does purging– Needs TVS
Computer controls OBDII diagnostics
Evap system problems
Failed purge valves / diaphragms rupturing
Plugged filters Failing TVS can cause cold flooding Loaded canister due to over full tanks Charcoal in carb. bowl indicates
defective canister
Early fuel evaporation systems
EFE system purpose
Helps a/f mixture vaporize on cold engine
Provide good cold driveability (cold air too dense and leans out mixture)
Improve cold emissions
EFE system purpose
Warms intake to prevent condensation of fuel
Prevents icing in carbs (temps can drop 66f when fuel vaporizes)
Four types of EFE
1. T.A.C. (thermostatic air cleaner) 2. EFE grid 3. Coolant heated intakes and throttle
bodies 4. Heat riser valve
T.A.C. components
Mode door– Cold air position for warm eng.– Warm air position for cold eng.
Uses manifold vacuum and vacuum motor to move mode door
Heat stove and pipe– Primary failure of emission tests
T.A.C. components
Sensor– Bleeds off vacuum at 100 - 120f– Must bleed off vacuum - can not trap it
Wax bulb type Manual movement (older asians)
T.A.C. problems
Stuck in hot air position will cause ping / NOx– Often caused by a plugged bleed off hole
Any missing piece can cause cold driveability problems
Cracked manifold sucks exhaust into air cleaner
EFE grid components
Electrical heater – Usually only, on carburetors and only on
primary bore(s) Commonly ceramic
EFE grid operation
Heats and mixes a/f mixture Controlled by switches or relay
– Usually powered up cold only
EFE grid problems
Grids melt Switches stick on Heater element opens
Coolant passages
Primarily icing controls Also helps warm intakes
Heat riser valve purpose
Directs exhaust to underside of intake manifold
Prevents condensation Improves vaporization Not necessary on PFI engines
Heat riser valve components
Vacuum with rod– Uses TVS
Bimetal spring On V engines valve will plug off one
side of exhaust when cold
Heat riser problems
Binding on shaft Stuck in cold mode causing ping and
NOx by overheating incoming a/f mixture
Valve disintegrating
Air systems purpose
To pump or allow air to be sucked into exhaust system– Completes combustion– Dilutes exhaust gasses– Gives O2 to cats– Heats O2 sensor
Two types - air pump and air suction (pulseair)
Air pump system
Air pump
Belt driven vane and rotor pump Some use electric air pumps Some means of filtered air intake
– Often using a centrifugal filter 1/2 Hp draw on engine
Diverter and gulp valves
Purpose: divert AIR away from exhaust on decel to prevent backfire
Gulp dumps AIR to intake– Similar to a decel valve / mixture control
valve Vacuum or electric controlled
Check valve
Purpose: to prevent exhaust from coming up into AIR system
Failed valves can cause melted hoses and diverter valves
Air manifolds and pipes
Rotting out causing backfire / exhaust leaks
Air on CCC cars
Computer controls routing of AIR system
Upstream cold vs. downstream warm Still diverts totally away during decel
Pulseair system
No pump Uses negative exhaust pulses Reed valves Can still divert or block off AIR Can be computer controlled Often mounted to air cleaner
Pulseair system problems
Back firing on decel if reed valves leak Melted stuff is melted if valves leak Can stick upstream
EGR systems
Purpose : flows exhaust gas into intake to lower combustion temps which lowers NOx
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
Three methods to obtain EGR
Floor jets– Egr at all times
Cam grinds– Egr at all times
Egr valves
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
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
Some use a vacuum amplifier– Works like vacuum relay
Often will have delay orifices and valves
Backpressure Transducer
Limits with exhaust pressures Exhaust pressures good load indicator Can modulate valve Many valves have built in transducers
– Positive valves vs. Negative valves
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
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
EGR testing
Egr movement under load– Some need to see VSS input
Vacuum present at valve Lift up at idle to check passages
Catalytic converters
Two types of converters
Oxidizing Reducing May be in one case
Oxidizing
First in 1975 Converts HC and CO to H2O, CO2 and
heat Uses precious metals platinum and
palladium
Monolith construction (honeycomb)
Ceramic coated with p&p Lots of surface area Very brittle Most common
Pellet construction
Aluminum oxide pellets coated with p&p Not as much surface area Very heavy Not easily damaged
Oxidizing operation
Needs O2 to convert HC and CO to H2O AND CO2– Gets O2 from lean a/f ratios, AIR systems,
missfires Light off at 500f, average temps 1400f
inside, 700f outside Abbreviated OC
Reducing cat
Converts NOX into N2, CO2, O2 Needs lack of oxygen and some CO to
work– Likes richer mix– Missfires provide too much o2
Uses rhodium
Three way or dual bed
First part or bed reducing
Gives off O2 to help second bed Needs CO which second bed eliminates
Second part oxidizing bed
Uses O2 from first part Can use air into cat behind first bed
Needs to be close to stoichiometric to work
Only found on cars with closed loop fuel
Problems and testing all types
Plugging– Abuse– If not abuse must find cause before
replacing Rich Leaded fuel Missfire Air system
Symptoms: Vacuum not always accurate Back pressure reading of > 3psi is
excessive Test at back pressure transducer, O2
sensor, AIR fitting, EGR
Efficiency loss
Symptoms: Loss can be due to lead, coolant, oil,
miles Aftermarket not as effective DO NOT USE USED CATS OBDII efficiency monitor
Efficiency testing
Temps 100-200f increase across cat Intrusive method
– Egr, AIR pipes (must seal), drilling hole– Need thin probe– Rivet holes up– Not at O2 sensor
Using the bible sticker underhood to id components