Operating Instructions - Snap-on Equipment

Interpretation2. Repair the vehicle to reduce regulated emissions gas concentrations.3. Retest the vehicle with the analyzer program to insure emissions are lessthan the baseline emissions.✓ Always repair for a maximum reduction in regulated emissionsgases. Repairs that just meet the standard will likely fail when retested.Five Gas Combination ReadingsThis chart lists some of the possible combinations of exhaust gas values and themost likely cause(s). Variables do not include secondary air.Legend: L = low; M = moderate; H = HighHLCO CO 2 HC O 2 NO Possible Problems / ConditionsLHHLLLLHThermostat or coolant sensor faulty. cold running engineThermostat or coolant sensor faulty - hot running engineL L L H L Exhaust leak after catalytic converterL H L H M Injector misfire, catalytic converter operating efficientlyHHHHHHHHHHHHHHMHHLLLLLLLLLLMLMLMLMLMHHHLLLLLLLLLLLLLLLLLLLLLLLLLLLHHHLMLMLMLMLMLMLMLMLMLMLMLMHHHHHHHHHHLMLMLMLMLMHHHLLLLLLLLLLLLHHHHHHHHHHLLLLLHHHLLLLLLLLLLLHLHHHHHHHHHLMLMHHMHInjector misfireCatalytic converter not workingCombination of rich mixture and vacuum leakAir-fuel ratio too rich:rich fuel mixtureleaking fuel injectorsincorrect carburetor adjustmentpower valve leakingchoke operating richfloat level too highair filter dirtyEVAP canister purge system faultPCV system problemengine control computer malfunctioningcrankcase contaminated with raw fuelall of the above with catalytic converter operating efficientlyrich mixture with ignition misfireAir-fuel ratio too leanlean fuel mixtureignition misfirevacuum leaks/air leaks (between air flow sensor and throttle body)EGR bad or vacuum hoses mis-routedcarburetor settings incorrectfuel injector badO 2 sensor bad or failingengine control computer malfunctioningfloat level too lowMajor engine fault;compression lowcamshaft lobe lift insufficientIgnition timing over advancedSpark plug wire grounded or openEngine control computer compensating for a vacuum leakL H L L L Good combustion efficiency and catalytic converter5-5