On Car Exhaust Gas Analysis (Petrol only)
Mak e SABB Model Z Year 1993
Exhaust Analyser was warmed up and calibrated. I put the analyser probe into the tailpipe and Made sure there was adequate ventilation.
Good combustion: HC + O2 + N2 = H2O + CO2 + N2
Pollutants from imperfect combustion: HC, CO, NOx
1. With the analyser probe sensing normal air, there should be Four Gas readings. The amount it would have given if it was not automatic, and then what it means:
CO 0% means: Safe air.
HC 0% means: No hydrocarbons in the air
CO2 0% means: no carbon dioxide in the air
O2 21% means: Normal oxygen in air
The right chart shows the gases in the exhaust that an infrared exhaust gas analyzer reads and how the gases change as the air/fuel mixture changes.When these gases are abnormal, look for this kind of problem and what is happening within the engine referring to the four gases:
| ▪ HC: misfire or bad burn When we have HC coming out the tailpipe, it is gasoline that didn’t burn in the combustion chamber or somehow escaped the flame of the combustion chamber. | ▪ CO: too rich |
| ▪ CO2: engine efficiency The more CO2 we create, the better our engine and cat were working. So we use CO2 as an indicator of engine efficiency | ▪ O2: too lean or just air depends on how leak free the exhaust and muffler are. |
| ▪ NOx: too hot or too lean |
The engine was already warm form driving to course.
So here are the preferred specifications at idle at lambda (14.7:1
CO less than 1%HC 50ppm or less
CO2 13- 15%
O21 3% or less
When the engine has warmed up, record the Four Gas readings:
The following happening within the engine referring to the four gases:
CO 0.5% show there is not a rich condition
HC 129 ppm slightly bad burn or an amount of misfire
CO2 15.1% shows good engine efficiency
O2 0.33% shows complete combustion and a leak free exhaust and muffler.
Run the warm engine at 2500 RPM, record the Four Gas readings:
Explain what is happening within the engine referring to the four gases:
CO 0.01% Shows the mixture is low within specification.
HC 17ppm this is a good reading showing low
CO2 15.18% good engine efficiency
O2 0.38% shows complete combustion and a leak free exhaust and muffler.
At idle, run the mixture rich with extra CRC, propane, LPG, or carburettor cleaner, and record the Four Gas readings:
Explain what is happening within the engine referring to the four gases:
CO 0.011% there’s no partially burned gas
HC 5ppm is low showing little or no unburnt fuel
CO2 15.16 The gas is completely burned up and the engine has good efficiency.
O2 0.08 less oxygen than before showing a more complete combustion as the oxygen was burnt with the extra CRC. So lambda would be closer to 1.
At idle, create a lean condition with an air leak or vacuum leak, record the Four Gas readings:
Explain what is happening within the engine referring to the four gases:
CO 0.004% is low and within specification.
HC 10ppm is low – Good combustion
CO2 14.57% good engine efficiency
O2 1.12% shows complete combustion and a leak free exhaust and muffler.
Accelerate the engine, by blipping the throttle a few times (don’t rev too high anddamage the engine), and watch how the gas readings change. The Four Gas readings when the CO is highest are Record:
within the engine there is still effecting combustion and good running refers to the four gases:
HC 6ppm is low Good combustion
CO2 14.8% shows good engine efficiency
O2 0.52% shows complete combustion and a leak free exhaust and muffler.
Optional: Make other changes to the engine at idle, such as turning on the air conditioning or rocking the steering wheel. Note the change you made:
Explain what is happening within the engine referring to the four gases:
CO 0.023% this is a good reading from a good mixture
HC 20ppm is within the range shows no misfire.
CO2 14.9% good engine efficiency and completely burned gas
O2 0.66% % shows complete combustion and a leak free exhaust and muffler.
To Disconnect one spark plug wire, ground it with a jumper wire, we switched from the SABB to a Toyota 4AFE without a CAT for the easy access to engine components, then recorded the Four Gas readings as the engine idles:
What is happening within the engine referring to the four gases:
CO 1.042%
HC 2200 ppm misfire or bad burnWhen we have HC coming out the tailpipe, it is gasoline that didn’t burn in the combustion chamber or somehow escaped the flame of the combustion chamber.
CO2 5.01% Bad engine efficiency The less CO2 we create, the worse our engine and cat were working. So this is an indicator of engine efficiency
O2 13.36% is high this means there is incomplete combustion so oxygen is left over or there is a leak in the exhaust pipe.
Disconnect the injector harness connector from one injector on an engine that has one injector for every cylinder: Record the Four Gas readings as the engine idles:
Explain what is happening within the engine referring to the four gases:
CO 0.9% approx at normal specification of below 1%
HC 205ppm is 4 times the normal specified range showing misfire or bad burn
CO2 4.71% bad, well below the 15% it should be at for efficient running
O2 14% to much oxygen indicating a lean mixture.Return the vehicle to good condition and proper adjustment.
2. The different readings you would get from a vehicle with a
catalytic converter(CAT) and a vehicle without one
catalytic converter(CAT) and a vehicle without one
Reduced HC, CO, NOx and increased H2O C02.
This is because the CAT converts HC to H2O, CO to CO2 and NOx is separated to nitrogen and oxygen witch 99% of air is made up of normally. For the specicalic readings compare the SAAB(CAT) against the Toyota catless) in the above quentions. Or Rich when 02 high volts (CAT cleans up NOx)
Lean when low volts (CAT cleans up HC and CO)
Light off point means the temperature that has to be reached for the cat to operate, and start to convert bad/toxic emissions into clean safe emissions.
On lambda, 02 sensors they have 1 Signal out,
2,3, or 4 these extra wires can be for
Heater positive
Heater Ground/earth
Signal earth
