The document discusses using 5 gas analysis to diagnose engine issues by looking at the relationships between oxygen (O2), carbon monoxide (CO), carbon dioxide (CO2), hydrocarbons (HC), and nitrogen oxides (NOx). Elevated levels of certain gases can indicate problems like a rich or lean mixture, misfiring, or an overloaded catalytic converter. Analyzing the 5 gas content allows technicians to quickly isolate problems, repair or replace faulty components, and get customers back on the road.
2. 5 Gas Analysis
• Now that you know about each gas individually, we will
use the following charts to see how the gases relate to
each other.
• Because of the Catalytic Converter these relationships
will look a little different on an emissions test, but are a
great place to start for determining why a gas or
combination of gases is out of range.
• CO2 is an combustion efficiency indicator.
• O2 is a lean condition indicator.
• CO is a rich mixture indicator.
• HC is a misfire indicator.
4. 5 Gas Analysis
• The converter can reduce a lot of NOX, HC & CO but is has
limits.
• If the gases are over 4% CO or 400ppm HC the Cat. not
only can’t process the gases it will destroy itself trying.
• So if you diagnosis and replace a failed converter and the
gas levels are near these amounts the new converter will
quickly burn out. Diagnosis the root cause first!
• The VIR does not tell the whole story, but using 5 gas
analysis you can narrow down the possibilities.
• Having a clear idea of what is not wrong saves diagnostic
time.
• Repairing one gas may create another gas failure.
6. • As you have seen, analyzing the 5 gas content of the
engine exhaust will allow you to isolate the problem
quickly, replace the faulty components or make
adjustments as required, and get your customer back on
the road.
• The most important thing to remember is that the PCM
adjusts fuel and ignition timing based on air volume.
• Your 5 gas analyzer is your best attack on driveability
complaints on all gasoline vehicles, old or new.
5 Gas Analysis