5 Gas Analysis

Another Rainharbor Production

1997

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)

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.

• The fully portable PXA1100 allows you to perform on the road tests under actual loaded conditions.

• Using the multiple record feature you can analyze the data back at the shop.

Analyze The Data

• Average emission reading or any portion of a road test

• Estimated Grams/Mile calculate an estimated I/M240 grams-per-mile

• ASM Analysis to analyze any snapshot

The PXA1100 provides data analysis no other analyzer can match:

Factory Repair Strategies

• The PXA1100 was designed around the new repair strategies such as GM’s SBD

• Average Emissions and Estimated Grams/Mile allow you to Baseline a vehicle’s emissions before repairs

• After repairs are made you can Verify emission reductions

• Perform O2 sensor analysis

• Test sensors, actuators, switches and voltage

• Min and Max capture on all meter modes

• Single and dual trace capability

• Auto setup automatically selects best settings

• Popup function menu

Oscilloscope & Meter Functions

Network the PXA1100 and the Tech1A or MasterTech

• The PXA 1100 networks with the Tech1A or MasterTech allowing the recording of scan data with gas data during a road test

Connect to a Pc for Even More Diagnostic Power

• Upload snapshots to a PC using Vetronix TechView for Windows for analysis

• Archive known good and problem road test data

• Display real-time data from PXA1100 and Tech1A or MasterTech on the PC

Additional Features

• Micro-Bench Technology no moving parts

• On-Screen Help

• Air Fuel Ratio Calculation

• Emissions Glossary 59 related terms defined

• On-Screen Maintenance and Calibration • Five Display Modes Bar, Line, Overlap, Custom, Numerical

• Optional RPM and Oil Temperature Display