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)
------------- E32 750iL,E36 M3
http://twrite.org/shogunnew/topmenu.html" rel="nofollow - 7 Series Tech Tips
|