5 Gas Analysis Three Reasons for Gas Analysis Identify engine performance and mechanical problems Test the running efficiency of the engine Test for.

5 Gas Analysi

s

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 (14% to 16%)

• Oxygen (O2) level in the exhaust indicates the fuel-air mixture.

• High O2=lean (HOT)

• Low O2=Rich (COLD)

• Opposite of CO (sort of)

OTHER EXHAUST EMISSIONS

• Water vapor (H2O)• Hydrogen (H)• Particulate carbon (C)

– Visible black soot

AND…..

ONE LAST THING

• Sulfur dioxide (SO2)– Created from combusting low sulfur

content in gasoline– In certain conditions the catalyst

oxidizes SO2 to make SO3 which combines with H2O to make H2SO4 (sulfuric acid) which forms hydrogen sulfide gas (rotten egg smell)

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

2&2 Before Testing

• Warm vehicle before testing– 2 minutes– @2000 to 2500 RPM– Check temperature of catalytic

converter to confirm operation• 500° + @ inlet• 50° to 150° hotter @ outlet

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 (WHY?)

• 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)

Using the PXA 1100For today’s Emissions

Programs

• I/M 240

• ASM

• Basic idle and cruise speeds

The PXA 1100 was designed for today’s emission programs, and is software

updateable for tomorrow’s.

Take It On The Road

• NOX failure typically occur under a loaded condition, which requires the vehicle to be driven on the road or on a dynamometer.

• Perform on the road tests under actual loaded conditions.

• Make multiple records (snap shots) so you can analyze the data back at the shop.