Operating Instructions - Snap-on Equipment

5InterpretationThe section includes:• Data Analysis Guidelines, page 5-2• Air-Fuel Ratio Effects, page 5-3• Correction Factors, page 5-3• Five Gas Combination Readings, page 5-5Interpreting gas concentrations under a given set of conditions becomes a matter of:• Understanding engine operation and the system or systems under test,• Understanding the relationships of exhaust gas concentrations to eachother, to the engine operation and to the catalytic converter, and• Applying logic to the possible causes, while eliminating those that are notprobable, and selecting the most likely of the possible causes.Applying logic becomes the diagnostic technique used to determine the cause ofunacceptable readings, together with a course of action that includes one or moreof the following variables:• Change engine speed, load, or both,• Defeat air management,• Enrich the fuel mixture with propane,• Create a vacuum leak to lean the fuel mixture, and• Use other test equipment such as an oscilloscope, vacuum gauge, or scanner.5-1