WS7 - Exhaust Gas Analysis ( Petrol only )

Leakage check first

Before check the emission, check the exhaust leakage first by block the tailpipe, and see any leakage.

Clean Emission for petrol engine:

Unite: ppm = parts per million

HC: The unburnt fuel 

CO: Carbon monoxide, cause by a rich mixture, not enough oxygen

CO2: Carbon dioxide, good thing we want from the engine

O2: Oxygen, cause by a lean mixture, not enough fuel

NOx: Nitrous oxide, cause by heat, pressure, lean mixture

Normal air:

CO: 0% - no CO in the air

HC: 4ppm - 4ppm unburnt fuel in the air

CO2: 0.02% - 0.02% CO2 in the air

O2: 20.91% - 20.91% O2 in the air

Idling:

When idling, CO CO2 O2 reading are acceptable, lambda show close to 1, just a little bit rich, but HC is high. Compares to other reading, misfire or weak spark may cause this.

Engine running at 2500 RPM

When the engine is running at 2500 RPM, the reading of CO and lambda shows the mixture is richer, HC indicate still have some unburnt fuel. Increase the engine RPM, ECU will spray more fuel, but don't have enough O2 to burn all of mixture to O2, cause the high reading of CO and HC.

At idle run rich by disconnect the MAP hose

When disconnect the MAP sensor hose, the MAP sensor thought the vacuum in the manifold is minimum, the throttle open maximum, gives the highest signal to ECU to spray maximum fuel. So the mixture is very rich, the reading of CO is high, and reading of lambda is low, reading of HC is high. O2 reaction to CO and CO2, high CO cause low CO2, when mixture is rich.

At idle run lean by create an air leak

When air leak into the manifold, the extra O2 will make the mixture lean. O2 all  The reading of O2 and Lambda is high. Lean mixture makes the spark ignite not very well and unburnt fuel increase and CO2 decrease.

Accelerate the engine by blipping the throttle a few times

When accelerate the engine by blipping the throttle a few times, the injector spray more fuel and mixture is rich, so CO is high, CO2 is low and Lambda is low. We blipping the throttle a few times, the combustion is not perfect cause the air/fuel ratio always changing, so there is unused O2 and HC into the exhaust and reading of them is high.

Disconnect one spark plug wire, ground it with a jumper wire.

When disconnect one spark plug, no ignition fire, so no combustion in that cylinder. Fuel and O2 are not reaction to CO2 or CO and H2O, so the reading of O2 and HC is high, CO2 is low and Lambda is high cause O2 is high. The temperature of the cylinder is very high but no combustion and a few of HC will reaction with O2 to H2O and CO, so CO is high.

Disconnect the injector harness from one injector

When disconnect one injector harness, no fuel be sprayed in and no combustion in that cylinder, so O2 and Lambda are high, CO2 is low. HC reading is a bit high because misfire or weak spark just talked when engine run idle.

Increase the engine load by rocking the steering wheel

When the engine load increased at idle speed, the IAC should let more air in and spray more fuel. Lambda and O2 show the mixture is lean, maybe the IAC valve opend not enough to let air in or the hose jammed by dirt.

Catalytic Converter
The catalytic converter reduce pollution of exhaust gas by chemical reaction.
Reactions:
NOx + CO-> N2 + CO2
HC + CO + O2 -> H2O + CO2
So, catalytic converter need engine run rich for CO to clean NOx and run lean for O2 to clean HC and CO.
The vehicle have catalytic converter the reading of HC CO and NOx should much lower then the vehicle don't have it.


Light off points
The light off temperature at which the catalytic converter begins to function ranges from 200 to 320 degrees, but the efficiency is not high. The normal operating temperature can range up to 650 to 870 degrees for high efficiency.


O2 sensors
1 wire: zirconia type or titania type. one signal, chassis ground
2 wires: zirconia type or titania type. one signal, one ground
3 wires: zirconia type or titania type. one signal, one heater positive, one heater ground. 
Wideband type. 2 signal wires and 1 ground
4 wires: zirconia type or titania type. two signal and two heater
Wideband type. 2 signal wires and 2 ground
5 wires: wideband type. 2 signal, 1 ground, 2 heater.