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Thread: exhaust gas analysis

  1. #1
    Join Date
    May 2004
    Location
    Japan
    Posts
    9,249

    Default exhaust gas analysis

    Here is some info from Bosch. Gas Analysis
    Bosch Technologies Group

    Three Reasons for Gas Analysis

    * Identify engine performance and mechanical problems
    * Test the running efficiency of the engine
    * Test for exhaust emissions against state and federal standards

    Combustion Chemistry and Gas Analysis.

    * The combustion process releases the energy stored in the fuel
    * Fuels consist basically of carbon(C) and hydrogen(H) referred to as hydrocarbons (HC).
    * Under ideal conditions all of the HCs would be converted to H2O, CO2 and heat.



    Combustion Chemistry and Gas Analysis.

    * Unfortunately this complete combustion is rarely if ever achieved
    * Short burn times, continuously changing mixture ratios and air temperatures, and combustion chamber quenching produce conditions which give rise to the formation of pollutants

    Pollutants

    * Incomplete combustion produces carbon monoxide (CO)
    * Unburned fuel produces hydrocarbons (HC)
    * High combustion temperatures produce oxides of nitrogen (NOX)

    Other Exhaust Gases

    * Carbon dioxide (CO2) is a product of complete combustion. Therefore the higher the level of CO2 the more efficient the engine is running.
    * Oxygen (O2) level in the exhaust indicates the fuel-air mixture.

    High O2=lean

    Low O2=Rich

    Gas Analysis as a Diagnostic Tool



    Gas analysis

    * Is a quick and accurate way to determine the running conditions of an engine
    * By observing the 5 gas readings and understanding their relationship to each other you can diagnose the 3 major engine areas:

    Fuel delivery

    Ignition

    Engine Mechanics


    High HC Only


    Hydrocarbons are unburned fuel. This can be caused by:

    Ignition Timing (base and advance)

    Vacuum Leaks (hoses, brake booster, manifold, evap. etc.)

    Ignition (misfires, coil breakdown, etc.)

    Mechanical (low compression, bad cam, etc.)

    Catalytic Converter Failures


    High CO Only


    * Carbon Monoxide is a result of incorrect fuel/air mixtures. Causes include:
    * For Carburetors (float level, power circuit, choke circuit)
    * For Injection (injectors, pressure regulator, temp sensor, MAP/MAF sensor)
    * For Both Systems (air filter, PCV, Evap, O2 sensor, air injection



    High Nox Only


    * NOX is caused by high combustion chamber temperatures. Check:
    * EGR (valve, controls, solenoids, passages, vacuum hoses)
    * Ignition Timing ( base and advance)
    * Engine Temperature (cooling system, fan restricted exhaust, Thermostat)
    * Vacuum Leaks (hoses, booster, evap, etc)
    * Mechanical (carbon deposits, converter, etc)

    High CO and HC


    * Normally, when HC and CO are high it is the result of a CO failure driving the HC high.
    * Correct for high CO first (Excessive fuel, restricted air, Evap., etc.)
    * If HC is still high, test as high HC (ignition, timing, mechanical, etc.)



    High CO and Nox

    * These problems are normally incompatible. If they occur on the same test they will most likely occur at different points on the drive cycle
    * Correct CO failure first
    * Retest and locate NOX failure in drive cycle and correct as NOX failure only



    HC and NoX

    * High HC and NOX normally occur as the result of a lean misfire. Check for:
    * Lean run (vacuum leaks, mixture problems, fuel delivery, etc.)
    * Mechanical (oil burning can cause high combustion chamber temperatures)



    CO, HC and NOX

    * This is a complete breakdown of the emission systems or multiple failures. Check:
    * Catalytic Converter (missing, damaged)
    * PCM (closed loop, wiring, etc.)
    * Drive cycle ( if failures occur at different points diagnose each failure separately)

  2. #2
    Join Date
    Feb 2004
    Posts
    4,894

    Default

    Great info!

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