Emissions
5-Gas
Vehicular Air Pollutants
Fuel
Crankcase Evaporation
Vapors 20%
20%
Exhaust
60%
Emitted Gases
• During combustion various reactions take place
between the combusting air and fuel mixture
• Five gases make up the majority of the resulting
exhaust
• Hydrocarbons (HC)
• Carbon Monoxide (CO)
• Carbon Dioxide (CO2)
• Oxygen (O2)
• Oxides of Nitrogen NOx
Optimal Combustion
• Input
• Air
• 21% Oxygen
• 78% Nitrogen
• 1% Argon, CO2 and other gasses
• Fuel (C8H15)
• Output
• H20
• CO2
• Nitrogen
Hydrocarbons (HC)
• Hydrocarbons are unburned fuel
• Hydrocarbons are made up of Hydrogen and
Carbon
• Gasoline (C8H15)
• Ethanol (C2H6O)
• Methanol (CH4O)
• Propane (C3H8)
• Excessive HC levels in the exhaust indicate
incomplete combustion
• HC should be less than 50 ppm
Carbon Monoxide (CO)
• Poisonous odorless gas
• Indicates a rich air/fuel mixture
• Not enough oxygen present to combine with all
of the fuel to produce CO2
• Should be less than .5%
Carbon Dioxide (CO2)
• Harmless gas
• Indicates efficient combustion
• Enough oxygen is present to combine with the
carbon and produce CO2
• Should be 12% - 17%
• Greenhouse gas
Oxygen (O2)
• Used during combustion
• Atmosphere contains 21%
• Exhaust contains .5% or less
• If A/F ratio is rich barely any will be present after
combustion
• If A/F ratio is lean more will be present after
combustion
• Extremely high levels of O2 may indicate an
exhaust leak or an improperly disabled AIR
injection system
Oxides of Nitrogen (NOx)
• Compound made up of one nitrogen atom and a
number of oxygen atoms
• NO, NO2, NO3, NO4
• NOx is produced when combustion temperatures
reach 1500 F
• NOx is produced rapidly when combustion
temperatures reach 2500 F
• NOx reacts with HC, O2 and sunlight to produce
smog
Emissions Testing
• Static
• Test is done at idle
• Gasses are measured as a percentage of the exhaust (I.e.
PPM, %)
• Illinois tests 1968-1979 vehicles this way
• Illinois tests AWD and 4WD vehicles this way
• Dynamic
• Called the IM240
• Test lasts up to 240 seconds
• Vehicle is driven on a dynometer to simulate city and
highway driving
• Illinois tests 1980-1995 vehicles this way
• Emissions are measured by total weight of emissions
• Grams per mile
IM240
IM240
IM240
Exhaust Gas Analysis
• Two gas analyzers
• HC and CO
• Four gas analyzers
• HC, CO, CO2, O2
• Five gas analyzers
• HC, CO, CO2, O2, NOx
Emissions Testing
• Pre-Cat (in front of the catalytic converter)
• Lets you test exactly what is coming out of the
engine
• Post-Cat (behind the catalytic converter)
• Tests what is actually coming out of the tailpipe
• Engine efficiency + converter operation
• Ensure the catalytic converter is up to
temperature
• Run engine at 2500 RPM for two minutes
Analyzer Hook-up
Attach
analyzer Attach
probe here analyzer
for Pre-Cat probe here
readings for Post-Cat
readings
You may have to drill a small hole
in the exhaust pipe to take a pre-
cat reading (either weld it shut or
install a fitting and plug)
Analyzer Hook-up
Emissions Diagnosis
• Possible gas combinations
• Low CO/High O2
• Indicates a lean mixture
• High CO/Low O2
• Indicates a rich mixture
• High HC/High O2
• Indicates a misfire/incomplete combustion
• High CO2
• Indicates efficient combustion
• High Nox
• Indicates high combustion chamber temperatures
Stoichiometric Gas Chart -
HC
Rich Lean
1000
HC (ppm)
75
Exhaust0
Level 500
ppm HC
250 100 ppm
or less
good
10:1 20:1
“Best” Range
14.6 to 14.8 to 1
Air/Fuel Ratio
Stoichiometric Gas Chart -
CO
Rich Lean
15%
CO
Exhaust
Level
% CO
About 1 %
0% Good
10:1 20:1
“Best” Range
14.6 to 14.8 to 1
Air/Fuel Ratio
Stoichiometric Gas Chart -
O2
Rich Lean
15%
Exhaust
Level
%
O2
0% .1 to 7
typical-
10:1 20:1 more,
“Best” Range
14.6 to 14.8 to 1 better
Air/Fuel Ratio
Stoichiometric Gas Chart -
CO2
Rich Lean
15%
Exhaust
Level
0% CO2
10:1 about
20:1
“Best” Range 8%
14.6 to 14.8 to 1
Air/Fuel Ratio
High CO/Low O2
• Indicates a rich mixture
• Possible Causes
• Leaking fuel injector
• High fuel pressure
• Faulty ECM input
• Low O2 Voltage
• Thermostat stuck open
• Plugged air filter
• Faulty canister purge valve
• Fuel saturated crankcase
• Leaking carb gaskets, sticking choke etc.
Low CO/High O2
• Indicates a lean mixture
• Possible Causes
• Clogged injectors
• Vacuum leak
• Low fuel pressure
• Faulty ECM input
• High O2 voltage
• Low float level, plugged jets, improper car adjustment
High HC/High O2
• Indicates a misfire (O2 and HC coming into the
engine but are not being completely burned)
• CO may be low, high, or normal
• Possible causes
• Ignition misfire
• Plugs, Wires, Cap, Rotor, Timing
• Low compression
• Lean misfire
• Rich misfire
• Sticking EGR
High NOx
• Indicates high combustion temperatures
• Possible causes
• Inoperative EGR
• Lean mixture
• High engine temperatures
• High intake air temperatures
• High compression ratio
High CO2
• Indicates efficient combustion
• Uncatalyzed levels around 13% indicate
efficient combustion
• CO2 levels should increase when the catalytic
converter starts operating
• 14.5 % CO2 indicates combustion is efficient
and catalytic converter is working
Low CO2
• If CO2 is below 10% proper
combustion/catalyzation is not occurring
• CO greater than .5%, O2 greater than CO
• Catalyst isn’t working properly
• CO greater than .5%, O2 lower than CO
• Catalyst isn’t working
• Air injection not providing enough O2 to catalyst
• Missing downstream pipe
• Switching valve problems
• Engine pumping out too much HC or way to much CO