Exhaust Gas Analysis (WS7)

Exaust Gas Analysis

We used a exhaust gas analyzer to do gas testing Honda civic 1992.

HC - means hydrocarbons - that is unburnt fuel caused by weak ignition spark, rich or lean air fuel mixture.

CO - Carbon monoxide - caused by a rich mixture , not enough oxygen.

Co2 - carbon dioxide - high percentage shows engine more efficient

02 - oxygen - shows air in exhaust. Caused by exhaust leak or lean mixture.

clean emissions :

 - HC under 100ppm (less is better)

 - CO under 0.1% (less is better)

 - CO2 over 13% (more is better)

 - O2 under 2% (less is usually better)

When the analyzer probe was sensing normal air  we got readings:

HC	CO	CO2	O2
0	0.003	0.01	20.84

We started the engine idling cold and got readings.

HC	CO	CO2	O2
413	1.633	14.83	0.72

This shows there is unburnt fuel in the exhaust and CO is high telling us the air fuel mixture is rich because the engine is cold and the ecu has made the mixture rich to heat up the engine. It is in open loop mode. The Co2 is also high telling the engine is running efficiently.

When the engine had warmed up the readings changed.

HC	CO	CO2	O2
48	0.089	15.33	0.43

This shows us that the engine has warmed up now and has gone to closed loop. The HC and CO has decreased telling us that the mixture is not rich anymore. CO2 has increased more telling the engine is running more efficiently. The fuel mixture is keeping stoichiometric to give out clean emission. 

When we increased the engine RPM to aobut 2500 we got readings.

HC	CO	CO2	O2
42	0.103	15.50	0.37

HC went down but the CO rises a little and oxygen drops a little. This tells us that the fuel mixture is bit rich then at idle. HC decreased a little which tells us that the fuel is getting burnt a little bit better than idle. CO2 is still high telling us engine is efficient. Emissions look pretty good.

Then we made the engine run rich by spraying in some propance gas. At idle we recorded the readings.

HC	CO	CO2	O2
2184	6.58	14.90	0.63

When we made the engine run rich HC and CO went up. There is a lot of unburnt fuel coming out the exhaust as there is not enough air at idle. CO increases as we have made the air fuel ratio rich.

Then we created an air leak to run the engine in a lean condition. The readings were recorded at idle.

HC	CO	CO2	O2
15	0.03	15.43	1.53

By making the engine run lean HC and CO decreases and O2 increased. CO deceasing telling us its a lean condition. HC decreased as theres is too much air and so more fuel gets burnt to compensate. O2 increases telling us that there is too much air and not enough fuel so excess unburnt oxygen comes out the exhaust.

We then accelerated the engine by blipping the throttle a few times and got readings.

HC	CO	CO2	O2
243	3.412	13.79	2.56

By blipping the throttle, the ecu makes the air fuel mixture rich as the engine is sucking more air in. As the engine gets rich CO increases. These is high HC and High O2 as well. This tells us that the spark was not strong enough to burn the fuel mixture thats why there is unburnt fuel and air in the exhaust. There was not enough time to burn all the fuel. 

Then we disconnected one spark plug and grounded it with a jumper wire to chassis. we got readings.

HC	CO	CO2	O2
1855	0.139	15.44	0.59

By this information HC is really high as one of the injectors were  disconnected so theres a lot of unburnt fuel coming out the exhaust.

Then we disconnected one of the connectors from the injectors

HC	CO	CO2	O2
34	0.007	11.22	6.30

By disconnecting one of the injectors we made the engine running like a lean condition. CO decreased telling us that its a lean mixture and there too much oxygen. HC decreased and oxygen highly increased telling us theres too much oxygen and not enough fuel.

We then returned the engine to good condition and everything in place.

Vehicles fitted with a catalytic converter has cleaner emissions as the 2 beds in the cat cleans emissions. HC, CO and oxides of nitrogen go into the cat and come out as carbon dioxide, water and nitrogen. Light off point means when the cat starts to work and clean emissions. It needs to reach a certain temperature to start working.

On oxygen sensors some of them have 4 or 5 wires, which are also for the heater. Because the oxygen sensor needs to be hot to work, the heater assists in heating up the oxygen sensor so its goes into closed loop quicker.Wires can be signal, signal ground, heater supply and heater ground.