FREE ASE PREP – Emissions Readings
Yes another page from my class at Abram Friedman Occupational Center given in January every year
If you ever needed help in understanding emissions readings, I think this page will help you.
The gas analyzers readings below indicate a vehicle at idle when the catalytic converter has not reached operating temperature.
HC 175 PPM CO2 12.5%CO 1.65 % O2 4.90%
Notice how the Hydrocarbons (HC) and Carbon Monoxide (CO) are slightly high.
Now look at the o2 readings, look how it’s higher than the CO. If this was a catalytic converter at operating temperature, I would be thinking a bad catalytic converter. After I confirmed the system was in fuel control and checked all the basics.
The readings below on the gas analyzer readings indicate an idle condition where the catalytic converter has reached normal operating temperature. Notice how hydrocarbons and carbon monoxide readings are greatly reduced.
HC 10 PPM CO2 15 % CO 0.01 % O2 .3% – Good Readings
NOTE:If you are use to lambda readings I will display them on the following readings. Lambda is a term that European manufacturers use to indicate air/fuel mixture balance. A reading of 1.00 indicates a balance air/fuel mixture. A reading less than 1.00 indicates a rich condition, more fuel than air. Also a reading greater than 1.0 indicates more air than fuel.
The gas readings below on the analyzer indicate a high concentration of (HC) Hydrocarbons and (O2) Oxygen. Vacuum leaks will show more at idle than at cruise speeds. This lean condition is one of the most common emission failures that show up at idle.
Also notice the Lambda readings indicate excess air or a lean condition.
This vehicle is showing a vacuum leak at idle.Now I’m going to show you the same vehicle readings below at 2500 RPM’S.
The gas analyzer readings below indicate good readings from the same vehicle but, this time the reading’s were taken at 2500 RPM. As the engine RPM increases, volumetric efficiency decreases and masks the vacuum leak.
HC 40 PPM – Co2 15.5% – CO 0.02 % – O2 O.3% – Lambda 1.01 – AFR 14.5 %
At 2500 rpm’s volumetric efficiency decreases, and masks the vacuum leak.
Now I’m going to show you some readings with a misfire, no matter the cause of the misfire, it will raise HC and O2 levels. Remember, in most cases, the gas analyzer will indicate a problem but will not tell you the problem, it’s still up to you to pin-point the cause of the high emissions.
HC 500 PPM – Co2 7.60% – CO .85% – O2 8.35 % – LAMBDA 1.38 – AFR 19.5%
This vehicle has an ignition misfire at idle
Now I’m going to show you some readings with a misfire, no matter the cause of the misfire, it will raise HC and O2 levels. Look at the increase in HC caused by the ignition misfire. This is a computer control vehicle and care should be taken because the CO may increase when the engine is in close loop.
The oxygen sensor sees the unburned o2 and this will increase the injector on time.
HC 610 ppm – CO2 9.05% – CO .39 % – O2 7.80% – LAMBDA 1.50 – AFR 21.6%
These readings are indicating an ignition misfire at 2500 RPM
The next readings are indicating a rich condition. In most cases, monitor the gases at idle and 2500 RPM.
HC 100 PPM – CO2 12.0% – CO 1.8 % – O2 .58% – LAMBDA .9665 – AFR 14.21 = Rich condition
High CO always indicate’s a rich condition
Remember it’s up to you to pin-point the cause of high emissions, the analyzer is just a tool. Properly understanding the emission readings is crucial in troubleshooting emissions.
HC 250ppm – CO 3.0% – O2 .2% – and CO2 8% – Rich Condition