Snap-On Diagnostics DGA 1000 Manual
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Snap-On Diagnostics DGA 1000 Manual

Diagnostic gas analyzer
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DGA 1000
Diagnostic Gas Analyzer

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Summary of Contents for Snap-On Diagnostics DGA 1000

  • Page 1 DGA 1000 Diagnostic Gas Analyzer...

  • Page 3: Table Of Contents

    Table of Contents Using this Manual ..............iii Safety Information .
  • Page 4 Table of Contents 4–O2/Check Install ............4-5 5–Gas Tag Values .

  • Page 5: Using This Manual

    Using this Manual This manual contains instructions for setup and use of the DGA 1000 Gas Analyzer and dynamometers. A table of contents and is provided to make this manual easy to use. Some of the information shown in text or illustrations is obtained using optional equipment.
  • Page 6 Using This Manual Equipment Damage The possibility of damage to vehicle or equipment is introduced by a signal word indicating this condition. Example: After extended testing, operate the engine at 1500 RPM with no load for several minutes with the cooling fan in place.
  • Page 7 Using This Manual Abbreviations The following abbreviations are used in this manual. current, amperage Air Injection Reaction carbon Compressed Natural Gas carbon monoxide carbon dioxide COMM communication Diagnostic Trouble Code exhaust gas recirculation flame ionization detector hydrogen hydrocarbons her tz km/h kilometers per hour pound...
  • Page 8 ®, EquiServ a unit of Snap-on Tools, is a registered trademark of Snap-on Tools Company. Copyright Information DGA 1000 Gas Analyzer Operating Instructions © 2001, Snap-on Diagnostics The information, specifications and illustrations in this manual are based on the latest information available at the time of printing.

  • Page 9: Safety Information

    Safety Information For your safety, read this manual thoroughly before operating the Analyzer System. The DGA 1000 Gas Analyzer is intended to be used by skilled, professional, and properly trained automotive technicians. The safety messages presented here and throughout this user’s manual are reminders to the operator to exercise extreme care when using this test instrument.
  • Page 10 Safety Information Read All Instructions Read all instructions and safety messages in this manual. All safety messages in this section contain a signal word, a three- par t message, and, in some instances, a symbol/pictorial. The signal word indicates the level of hazard in a situation. •...
  • Page 11 Safety Information Risk of fire. • Wear safety goggles and protective clothing, user and bystander. • Do not position head directly over or in front of the carburetor or throttle body. Do not pour gasoline down the carburetor or throttle body when cranking or running the engine, when working with fuel delivery systems or any open fuel line.
  • Page 12 Safety Information The engine compartment contains electrical connections, and hot or moving parts. • Do not place test equipment or tools on fenders or other places in the engine compartment. • Keep yourself, test leads, clothing, and other objects clear of electrical connections and hot or moving engine parts.

  • Page 13: Introduction

    Introduction The DGA 1000 Gas Analyzer is a versatile test instrument for analyzing exhaust gases of internal combustion engines. When used with other tools and equipment, the analyzer can also detect and locate ignition, fuel, exhaust, emission control, and engine service problems.

  • Page 14: Functional Description

    Introduction Functional Description Front Panel The front of the analyzer includes controls for operating the unit, the monitor screen for viewing tests and the printer, which provides a written record of test results. Descriptions of the items labeled on the analyzer front view follow Figure 1-1 Figure 1-1: Analyzer—Front Panel View A —9"...
  • Page 15 Introduction D —Vehicle Set-up Key Use to set-up the vehicle information when in emissions measurement display. E —PRINT Key Use to: — Access message/customer input screen. — Press TWICE to start printing. F —Freeze/Store Key Use to: — Stop or freeze all test screen information necessary for saving a screen to memory.

  • Page 16: Back Panel

    Introduction Back Panel Important features for analyzer operation and maintenance are located on the back panel. Descriptions of the items labeled on the analyzer back panel follows Figure 1-2 Figure 1-2: Analyzer—Back Panel View A —Filter Sample, secondary in-line filter. B —Printer 24 columns.
  • Page 17 Introduction G—Voltage Switch Use this switch to select either 230VAC or 115VAC power input. H —Auxiliary Outlet Use this outlet to connect optional equipment. J —Filter Bowl Water Drain Input Water from filter bowl inlet port. K —Gas Sample Exhaust [1] Outlet Vehicle gas sample exit port from NO cell.

  • Page 18: Screen Displays

    Introduction Screen Displays The screen displays a number of universal symbols to allow easy navigation around the various menu and screen displays using the ENTER and ARROW key pad. Figure 1-3 Additional details of these symbols follow Use the arrow keys ( ) followed by the ENTER key to select items in Group 1 functions.

  • Page 19: Action Indicators

    Introduction Action Indicators On the lower left side of the Measurement Screen, a status symbol is displayed when a fault or error occurs. Auto zero/Auto calibration A pre-warning that indicates a Auto zero/Auto calibration is required. Auto zero/Auto calibration is automatically performed by the analyzer when measurements are stopped.

  • Page 20: Function Selection Symbols

    Introduction Function Selection Symbols Selection symbols, shown in Figure 1-4 , display on the lower right of the screen. Figure 1-4 : Selection Symbols on Measurement Screen Warnings/Errors Select with arrow keys, and press ENTER to get information about the warning symbols which can appear on the left side of the screen.
  • Page 21 Introduction Toggle RPM/Oil Temp Select with arrow keys, and press ENTER to switch between RPM indication and oil temperature indication on the screen. When the NO Measurement option is not installed, both RPM Measurement and Oil Temp are shown on the screen.
  • Page 22 Introduction Figure 1-5 : Clearing Data Buffer(s) Clear Buffers Select to clear all data in memory. Data Memory Buffer 1 Select to clear data memory buffer 1. Data Memory Buffer 2 Select to clear data memory buffer 2. Left Arrow Key Select left arrow key ( ) to return to Measurement Screen.

  • Page 23: Screen Navigation Symbols

    Introduction Screen Navigation Symbols There are also symbols used to indicate the presence of additional screens and selections. The following symbols indicate: You can move to the previous line. There is a previous screen. You can move to the next line. There is a next screen.

  • Page 24: Optional Accessories

    Introduction Optional Accessories Standard Keyboard (not shown) The keyboard can be used to access and exit a screen, or navigate within a screen. The function of the keys on the keyboard are the same as for a normal PC. The functions of the keyboard are as follows: •...

  • Page 25: Optional Remote Control Keypad Kit

    Figure 1-8: Remote Control Keypad A —Remote Control Unit Use the keys to access, navigate, or exit the DGA 1000 Gas Analyzer software from a remote location. B —Setup Use this key for the Vehicle set-up menu.
  • Page 26 Up Arrow — Press to move cursor toward top of screen. CONT — Not used for DGA 1000 Gas Analyzer emissions testing. Right Arrow — Press to move cursor toward right side of screen. — Not used for DGA 1000 Gas Analyzer emissions testing.

  • Page 27: Specifications

    Introduction Specifications Power Supply Input Voltage 115VAC or 230VAC Watts Shipping Weight 41.9 lbs (19 kg) Dimensions Height 16.50" (423 mm) Width 12.75" (326 mm) Depth 22.88" (586 mm) Measurements Range/Resolution Accuracy 0.000–9.999 ±3% 10.00–14.00 ±5% 0.00–18.00 ±5% 0–2000 ±3% 2000–5000 ±5% 5000–9999...

  • Page 28: General Setup Tips

    Introduction General Setup Tips Read and follow the procedures in this manual. Keep the probe tip openings clean and free of debris. Do not place the probe tip in liquids or allow liquids to be drawn into the analyzer sampling system. Contamination affects the accuracy of any tests.

  • Page 29: Standard Lead Connections

    Introduction Standard Lead Connections To Analyzer 1. Make sure the on/off switch (G) is set to off (O). See Figure 1-9 Figure 1-9 : Front Panel 2. Plug the power cord into the AC power source (F) on the back panel of the analyzer. Plug the other end into a standard 120VAC grounded electrical outlet.

  • Page 30: Connecting To A Vehicle

    Introduction Figure 1-10 : Back Panel An optional 12V power adapter, part number 2-2650, is also available. This allows the analyzer to be powered by a vehicle battery. 3. Inser t the keyboard connector to the keyboard por t (U). 4.

  • Page 31: Connecting The Optional Temperature Probe To The Vehicle

    5. Inser t the probe into the dipstick tube until the rubber stop comes in contact with the dipstick tube. Since the DGA 1000 Gas Analyzer was released, two types of oil temperature probes have been used (Euro and US probe).

  • Page 32: Start-Up

    Introduction Start-up 1. Make lead connections to the analyzer and the vehicle. Refer to To Analyzer‚ page 1-17 and Connecting to a Vehicle‚ page 1-18 . 2. Turn the analyzer power switch on (I). The Start-up Screen displays. 3. Allow the analyzer to perform Warm-Up, Auto zero calibration and HC hang-up check.

  • Page 33: Analyzer Screen Display Features

    Analyzer Screen Display Features This chapter explains the purpose of each screen, the symbols on each screen, and how to access and exit the screens. Before performing measurements make sure all test setup information of the vehicle under test is correct. Press the vehicle setup key ( ) to program setup information.

  • Page 34: Co Corrected

    Engine speed measured in revolutions per minute, and oil temperature measured in degrees Fahrenheit. CO Corrected The DGA 1000 Gas Analyzer performs a CO measurement correction when CO and CO are less than (<) 15% for gasoline. Figure 2-2 .
  • Page 35 Analyzer Screen Display Features The following is a chart showing the resulting content of a CO correction: Figure 2-2 : Corrected CO...

  • Page 36: Lambda And Afr Calculation

    Analyzer Screen Display Features Lambda and AFR Calculation The DGA 1000 Gas Analyzer uses the Brettschneider formula to λ calculate Lambda ( ) and Air Fuel Ratio (AFR) values during the emission tests. Lambda (λ λ λ λ ) and Catalytic Converter Efficiency Lambda is another characterization of the stoichiometric perfect λ...

  • Page 37: Air-Fuel Ratio And The Stoichiometric Point

    Analyzer Screen Display Features Air-Fuel Ratio and the Stoichiometric Point For each fuel used in an internal combustion engine, there is an air-fuel ratio that optimizes the combustion process. For common gasoline, that ratio is 14.7 pounds of air to 1 pound of gasoline. This ratio varies with each type of fuel.

  • Page 38: Test Menu

    Analyzer Screen Display Features Test Menu This section details menu selection items and their submenus. Figure 2-5 : Menu Using the arrow keys ( ), move to the Home icon and press ENTER. The Test Menu displays as shown Figure 2-5 This section contains a complete description of each test function shown in Figure 2-5...
  • Page 39 Analyzer Screen Display Features Figure 2-6 : Maintenance Screen Leak check (vacuum) This test determines if there is an air leak in the gas sample handling system of the analyzer. Follow the instructions on the screen. Press Enter or the right arrow ( ) to begin the test.
  • Page 40 Analyzer Screen Display Features Gas tag values Use this function to enter calibration gas bottle values for gas calibration. The calibration gas values must be entered to perform a gas calibration. Refer to Chapter 4–Maintenance Gas calibration Use this function in conjunction with gas tag values to perform a gas calibration.
  • Page 41 Analyzer Screen Display Features Language Select a language for the analyzer display. (Currently only English is available.) Date and Time Use to change or reset the time display in the right-hand upper corner of the screen. — To change press ENTER or arrows ( ).
  • Page 42 Analyzer Screen Display Features Print-out Header Set up Enter the shop name, address, phone number, etc. to print as a header on the test results printout. Figure 2-9 : Print-out Header Set-up Screen After entering the information, press the Esc key to exit and save. Print-out Message Enter standard field names for the customer information you want to use.
  • Page 43 Analyzer Screen Display Features 5. System Status System information about the DGA 1000 Gas Analyzer displays on this screen. Only a Service Representative can modify these items and the information may be requested when you require service. System status information can NOT be changed by the operator.
  • Page 44 Analyzer Screen Display Features 1. Hardware and Software (View Only) Shown is an example of the DGA 1000 Gas Analyzer hardware and software configuration display in Figure 2-13 Figure 2-13 : Hardware and Software Screen 2. Settings (View Only) Three Settings Screens display DGA 1000 Gas Analyzer settings.
  • Page 45 Analyzer Screen Display Features Figure 2-15 : Settings Screen 2 Figure 2-16 : Settings Screen 3 3. Service Dates (View Only) Service Dates Screen gives an overview of last checks and calibrations. It also shows when the NO cell and O cell need to be replaced.
  • Page 46 Analyzer Screen Display Features 4. Gas Tags Gas Tags Screen shows the gas values used during analyzer calibration. These values can be set by the operator using this page. The values in Figure 2-18 are recommended. Figure 2-18 : Gas Tags Screen Type 4 NO is used only when the analyzer has the NOx option installed.
  • Page 47 Analyzer Screen Display Features 6. Diagnostics (View Only) Diagnostics Screen displays the number of service entries performed by the Service Representative. Figure 2-20 : Diagnostics Screen 7. Approval Settings Approval Settings are only accessible to a Service Representative. 8. System Status Printout When the System Status Printout Screen displays, press the right arrow key ( ) to print.
  • Page 48 Analyzer Screen Display Features 2-16...

  • Page 49: Vehicle Testing

    Vehicle Testing This chapter contains information necessary to: • Prepare a vehicle for testing, • Perform tests, and • Evaluate test data. Preliminary Checks Conduct a thorough inspection of the vehicle before performing any analysis or troubleshooting with the analyzer. Accurate engine performance diagnosis depends on proper operation of related components or systems.
  • Page 50 Vehicle Testing Exhaust System • Exhaust pipes and connections — Connections should be tight and with no obvious leaks or obstructions. • Catalytic converter • Air management system — Check valves should not leak. • Diverter valve/air switching valve — Valve should not stick or leak into closed off port. Electrical System •...

  • Page 51: Testing Tips

    Vehicle Testing Testing Tips Read and follow the safety instructions in Safety Information this manual. Always comply with the governing emission control standards and regulations in your locality when testing exhaust emission levels. Check vehicle manufacturer specifications and procedures before testing. Do not test exhaust emissions on vehicles that are smoking excessively or are in obvious need of engine repair.

  • Page 52: Setting Up The Vehicle

    Vehicle Testing Setting Up the Vehicle For all types of vehicle testing, gas display, TSI procedure or catalytic testing, some vehicle information should be entered into the analyzer as described in this section. Once this action is completed, all types of test can be performed without reentering the data.
  • Page 53 ) is pressed — Limits set in the Setup ( ) Menu are stored in memory and retained when there is no power to the DGA 1000 Gas Analyzer . • The second set is used with the TSI procedures function only for the Catalyst Testing procedure.
  • Page 54 Vehicle Testing To set limits for the vehicle being tested, use the down ( ) arrow key to edit limits or press 4. The Set Limits Screen displays. Arrow up or down ( ) to the item you want to change and press ENTER.
  • Page 55 Vehicle Testing : Set 1 Limit Screen 1 ) L J X U H    : Set 1 Limit Screen 2 ) L J X U H    When settings are changed, and a measurement was previously stored, the ongoing data in the memory is cleared.
  • Page 56 Vehicle Testing : Measurement Screen ) L J X U H    General Emissions Measurements After setting up the vehicle, RPM selector, fuel type, limits on/off, and edit limits used, use the Diagnostic Gas display to read various emission gases. Refer to Chapter 7–Diagnostic Technique for more information.

  • Page 57: Two-Speed Idle (Tsi) Test

    Vehicle Testing Two-Speed Idle (TSI) Test The “typical” TSI procedure function contains three different procedures: • Non-Cat 1 (single speed test) • Non-Cat 2 (single speed test) • Catalytic Test (two speed test). The Limits function, if turned on, can be used for all three tests. Remember, any limits entered only apply to for as long as the same vehicle is being tested.
  • Page 58 Vehicle Testing 12. Follow the screen prompts. Note the test can be done without RPM or oil temperature by pressing the ENTER with the arrow key. 13. When the display reads BRING RPM INTO WINDOW, depress the accelerator pedal to increase engine speed to the desired speed.

  • Page 59: Catalytic Efficiency Test

    Vehicle Testing Catalytic Efficiency Test This test is accessed from the Test Menu and can be used to diagnose an excessive emissions failure resulting from a damaged or tampered catalytic converter. A specified amount of propane, is flowed through a preheated converter and the resulting CO HC levels are measured at the tailpipe with the exhaust gas analyzer.

  • Page 60: Introduction

    Vehicle Testing Introduction Use the optional catalytic converter test kit with the DGA 1000 Gas Analyzer to determine if a catalytic converter is capable of functioning properly and to diagnose emissions failures that are a result of a damaged or tampered catalytic converter.

  • Page 61: Catalytic Converter Test

    Vehicle Testing Catalytic Converter Test The Catalytic Converter Test is performed manually and is fully under the operator’s control. This allows the test to be run even if engine RPM measurements are not easily accessible. In that case, follow the screen prompts to complete the test. The test must be completed within five minutes after vehicle warm-up or the catalytic converter may cool and the test results may be invalid.

  • Page 62: Pre-Test Inspection

    Vehicle Testing Pre-test Inspection During emission troubleshooting, the catalytic converter should be the last item to be tested and/or repaired. Perform the following inspection before starting the catalytic converter test. Make sure all diagnostic trouble codes are repaired. Make sure all engine controls and emission controls are operating correctly.

  • Page 63: Before Testing

    Vehicle Testing Before Testing Assemble the following equipment and be sure to have the information described in this section available. Propane supply tank. Flow meter, part number 1-15381. The flow rate is based on the engine displacement and exhaust system configuration. Propane enrichment assembly, part number EAA0259L00A.
  • Page 64 Vehicle Testing The catalytic converter test should be conducted within five (5) minutes of preheating the converter. It may be necessary to connect a battery charger to the vehicle if cranking RPM drops dramatically during catalytic converter testing. Disabling ignition system may require: —...

  • Page 65: Disabling The Fuel System

    Vehicle Testing Disabling the Fuel System Refer to the vehicle manufacturer’s procedure for disabling the fuel system. Some common methods of disabling the fuel system follow. – Most Ford vehicles are equipped with an inertia switch. Lifting the plunger Inertia Switch on the top of the switch deactivates the fuel pump.

  • Page 66: Catalytic Converter Test Set-Up

    Vehicle Testing Catalytic Converter Test Set-up Two people are required for this procedure. 1. Connect the oil temperature probe and RPM pickup. Insert the exhaust probe. 2. Input the vehicle information. 3. Start procedure. Information displays on the Start Procedure Screens. Beginning with step 4, items shown in Bold type are instructions which display directly on the screen.
  • Page 67 Vehicle Testing 9. Are you sure that ignition was disabled? NO (make choice) 10. Are you sure that injection was disabled? NO (make choice) 11. Are you sure that the engine was cleared of residual gases? NO (make choice) 12. Adjust propane to a flow of: Example (based on default engine displacement value of 2000cc): —...
  • Page 68 Vehicle Testing 3-20...

  • Page 69: Maintenance

    Maintenance The DGA 1000 Gas Analyzer is a precision diagnostic instrument that requires little maintenance. The maintenance and service procedures presented in this chapter are those which the operator can perform. All other services should be performed by an authorized Service Representative.

  • Page 70: Sample System

    Maintenance Sample System : Analyzer—Back Panel View ) L J X U H    The analyzer contains three filters and a charcoal filter to protect and extend the analyzer sample system life. Three filters, A, C and E shown in Figure 4-1 , must be serviced at regular intervals.
  • Page 71 Maintenance E —Primary Filter Bowl Assembly • Removes moisture and other exhaust contaminants that are potentially harmful to the analyzer. • Inspect daily and replace every two week with par t number 7096E9062-77. — To replace the filter, unscrew the locking ring, which connects the bowl to the upper housing, to gain access to the filter.

  • Page 72: 1- Leak Check Vacuum

    Maintenance There are a number of functions in the Maintenance Menu. Some may be used to insure analyzer performance, some that should not be used and some that cannot be used. The following choices are available on the Maintenance Menu: Leak Check Vacuum Leak Check Gas Gas Calibration Check...

  • Page 73: 4-O2/Check Install

    Maintenance 4–O /Check Install This function must be used when the O is replaced. It is not necessary to use this function at any time other than O cell replacement. 5–Gas Tag Values Use the Gas Tag Values function to enter calibration gas bottle values of the calibration gas used for gas calibration.

  • Page 74: Test Leads

    Maintenance 1. In the Test Menu, select item 3, Maintenance, and then item 6, Gas Calibration. 2. Connect the calibration gas regulator to the calibration gas port, item P in Figure 1-2 Make sure the regulator is set properly for proper pressure, 5–10 psi output.

  • Page 75: Keyboard And Remote Control

    Maintenance Keyboard and Remote Control Clean the keyboard and the remote control with a mild detergent and a soft cloth. Do not use solvents acetone, benzine, gasoline, etc. They can damage plastic components and affect correct operation of the components. Clean any surface spills immediately to protect the keyboard and remote control.

  • Page 76: Sample Probe And Hose

    Maintenance Sample Probe and Hose Probe Check Periodically check the holes at the end of the probe for dirt and debris. Clean Disconnect the hose from the analyzer at the sample inlet. Using a small pointed tool, clean the probe and blow away any debris using compressed air.

  • Page 77: Troubleshooting

    Maintenance Troubleshooting Use the information in this section to solve equipment problems. Messages On the Measurement Screen, status symbols display when the analyzer fails to perform an action or fails a test. : Status Symbols ) L J X U H    Auto zero/Auto calibration The Auto zero/Auto calibration symbol is a pre-warning which indicates that an Auto zero/Auto calibration is required.

  • Page 78: Control And Error Status

    Maintenance Control and Error Status When this symbol is selected, the analyzer shows more information about the control and error status of the analyzer. The control and error status information consists of two screens. The first screen gives general information about the condition of the analyzer.
  • Page 79 Maintenance LOW FLOW Solution: The Gas filter or Exhaust Sample probe is clogged. Replace Gas filter or clean Exhaust Sample Probe. NEW O SENSOR NOT WITHIN LIMITS Solution: Contact your Service Representative. NO FLOW Solution: The analyzer pump is not running. Try to restart the pump by activating and deactivating the STANDBY mode.

  • Page 80: Accessory Kit

    Maintenance Accessory Kit The DGA 1000 Gas Analyzer is delivered with an Accessory Kit, part number 7009E9321-24. The kit is used to make the analyzer complete for first operation. The kit contains the following parts: Power cord............6001-0197-01 Exhaust probe assembly ........7009-1869-00 Exhaust hose 30 ft.

  • Page 81: Fundamentals

    Fundamentals This chapter contains essential information required to understand and interpret analyzed combustion by-products and information provided by the analyzer. Included is a description of how and where combustion by-products form in an engine and common methods used to help reducing their formation. Combustion and Air-Fuel Ratios In a gasoline-powered internal combustion engine, normal combustion is burning a compressed mixture of hydrocarbon fuel...

  • Page 82: Combustion Emissions

    Fundamentals The ideal air-fuel ratio for perfect combustion in a gasoline engine is 14.66:1, commonly referred to as 14.7:1. This is the stoichiometric ratio or stoichiometric fuel mixture. Under perfect conditions, the combustion of a stoichiometric air and fuel mixture results in carbon dioxide (CO ), water (H O) and nitrogen (O...

  • Page 83: Oxides Of Nitrogen (Nox)

    Fundamentals Oxides of Nitrogen (NO Air in the atmosphere, and air admitted into the combustion chamber of an engine, consists of about 78% nitrogen (N ) and about 21% oxygen (O ) by volume. Nitrogen does not contribute to, or detract from, combustion. When exposed to heat above 2000°F (1093°C), oxygen and nitrogen combine.
  • Page 84 Fundamentals Some of the devices and factors that affect the formation of NO are: The following descriptions should be considered individually, that is with minimal effect from other dynamic variables. • Exhaust Gas Recirculation (EGR) — EGR dilutes the air-fuel mixture, lowers combustion chamber temperature, and reduces flame speed.
  • Page 85 Fundamentals • Carbon Build-up — Carbon in the combustion chamber reduces combustion chamber volume. This increases compression pressure and increases the air and fuel mixture temperature which contributes to NO formation. • Fuel Octane — Low octane fuel burns faster and less controlled than higher octane fuel.

  • Page 86: Hydrocarbons (Hc)

    Fundamentals Hydrocarbons (HC) HC is an organic compound composed of one hydrogen (H) and one carbon (C) atom. The HC in gasoline engine exhaust is unburned gasoline vapor that is measured in parts per million (ppm). HC levels in engine exhaust vary with the air-fuel ratio. Figure 5-4 : Hydrocarbons Versus Air-Fuel Ratio The lowest HC emissions occur at an air-fuel ratio of about 16:1.

  • Page 87: Carbon Monoxide (Co)

    Fundamentals Carbon Monoxide (CO) CO is an exhaust by-product formed when combustion occurs with less than the ideal volume of oxygen (rich fuel mixture). This combines a carbon atom with an oxygen atom. Carbon in the combustion chamber comes from the HC fuel, and oxygen from inducted air.

  • Page 88: Carbon Dioxide (Co2)

    Fundamentals Carbon Dioxide (CO is a combustion product formed when one carbon atom bonds with two oxygen atoms, and by the oxidation of CO in the catalytic converter. Unlike CO, CO is comparatively harmless. is a good indicator of combustion efficiency because its volume in the exhaust peaks just before the stoichiometric air-fuel ratio.

  • Page 89: Oxygen (O2)

    Fundamentals Oxygen (O The level of O in exhaust gas is an indicator of air-fuel ratio leanness. The O is present in the air the engine inducts and mixes with the HC for combustion. Since the atmosphere is about 21% , the percentage of O in the exhaust gas after combustion indicates air-fuel ratio leanness.

  • Page 90: Interpreting Air-Fuel Ratios And Emissions

    Fundamentals Interpreting Air-Fuel Ratios and Emissions The relationship between the air-fuel ratio and exhaust gases monitored by the analyzer are: • HC is lowest when the air-fuel ratio is ideal because most of the fuel is consumed in combustion. Richer or leaner mixtures, or ignition problems cause HC to increase because of incomplete combustion.

  • Page 91: Stoichiometric Fuel Mixture

    Fundamentals Stoichiometric Fuel Mixture The stoichiometric air-fuel ratio (14.66:1) is near the point where the emission levels drastically change. The stoichiometric air-fuel ratio, where the HC and CO levels are lowest, is as close to perfect combustion as can be attained. Figure 5-8 : Major Combustion By-products Versus Air-Fuel Ratio The term lambda is often used instead of air-fuel ratio.

  • Page 92: Catalytic Converters

    Fundamentals Catalytic Converters The first attempt at reducing emission levels in automobiles was to get air-fuel ratios as close to stoichiometric as possible. However, even engines designed for low emissions, and that are operating properly, may not have HC and CO emission levels low enough to meet clean air standards.
  • Page 93 Fundamentals Figure 5-11 : HC and CO Oxidation in a Catalytic Conver ter Oxidation of any compound requires an abundance of O . Some engines use Air Injection Reaction (AIR) or pulse air type systems to provide the supplemental O needed.
  • Page 94 Fundamentals Figure 5-12 shows NO versus air fuel ratio after being treated by a three-way catalytic converter. NO levels are typically low when the air-fuel ratio is more rich than stoichiometric. When the air-fuel ratio is near stoichiometric and more lean than stoichiometric, NO levels increase, then fall to slightly lower values as the air-fuel mixture continues to get leaner.

  • Page 95: Vehicle Testing Procedures

    Vehicle Testing Procedures Testing Gasoline-Fueled Vehicles Diagnosis from the exhaust gas sample can be difficult on an engine that has any combination of the following systems: • Catalytic converter, • Computer control with an O sensor and fuel injection, • Air management, •...

  • Page 96: Data Collection Modes

    1. Insert the sample probe into the vehicle tail pipe. Make sure that the sample probe is fully inserted. 2. Switch on the DGA 1000 Gas Analyzer and leave it in the Measurement Screen. 3. Read the exhaust concentrations on the screen.

  • Page 97: Testing Under Load

    Vehicle Testing Procedures Testing Under Load When sampling exhaust gases, NO readings can be observed at idle, low speeds and low load operating conditions. However, since NO is mainly formed under load (high combustion chamber temperatures), effective testing must be performed under load using a chassis dynamometer or by driving on the road.

  • Page 98: On-Road And Dynamometer Testing Under Load

    Vehicle Testing Procedures On-Road and Dynamometer Testing Under Load Exhaust emission testing with a chassis dynamometer can be performed in the same way a stationary vehicle is tested in the shop bay, except that the engine operates under load, simulating operating conditions on the road, except for traffic, turning corners and weather conditions.
  • Page 99 Vehicle Testing Procedures 5. Insert the sample probe into the tail pipe and secure to prevent it from falling out of the tail pipe. When performing this test on the road, the probe can be secured by tying the exposed metal portion of the sample probe with "mechanics wire”...
  • Page 100 Vehicle Testing Procedures On-Board Diagnostic (OBD) II Drive Cycle Disconnecting the vehicle battery, powertrain control module (PCM) or certain components controlled by the PCM on vehicles with OBD II may cause a “not ready for I/M testing” condition. In this condition, the vehicle will not perform properly. Following a specific OBD II Drive Cycle restores normal operation of the PCM.

  • Page 101: Air Pump Test

    Vehicle Testing Procedures Air Pump Test An engine-driven air pump is sometimes used to lower CO and HC by pumping fresh air into the exhaust system at pressures up to approximately 5 psi (0.35 bar). This supplies additional O to the hot gases to allow continued combustion, resulting in lower levels of HC and CO at the tail pipe.

  • Page 102: Carburetor Adjustments

    Vehicle Testing Procedures Testing Tip Some systems may divert air pump output to the air cleaner housing or the atmosphere under some conditions. This could lead to incorrect test results. Before replacing components, understand the system operation. Test 1. Record exhaust gas readings while the engine is at 1500 RPM.

  • Page 103: Lean-Misfire Adjustment Test

    Vehicle Testing Procedures Lean-Misfire Adjustment Test 1. Observe the CO reading. — If greater than zero, proceed to step 2. — If not greater than zero, turn the mixture screw(s) to enrich the mixture. If there are two adjustment screws, adjust both screws an equal number of turns. 2.

  • Page 104: Accelerator Pump Test

    Vehicle Testing Procedures Accelerator Pump Test When the throttle is opened rapidly, engine speed should increase without hesitation. If there is a hesitation, the problem could be a malfunctioning accelerator pump. Test 1. Note the CO reading at idle. 2. Note the change in the CO readings from the idle readings for each throttle change: —...

  • Page 105: High Fuel Level In Float Chamber Test

    Vehicle Testing Procedures 4. While holding the fast idle cam with one hand, quickly open and return the throttle to the same fast idle position. It is possible for the engine to backfire during this test. Never position yourself in a way that could expose you to the heat/flame of an intake system backfire.

  • Page 106: Combustion Gases In The Cooling System Test

    Vehicle Testing Procedures Combustion Gases in the Cooling System Test Use the cooling system of a vehicle as a window for evaluating the condition of an engine when a blown head gasket, cracked engine block, or cracked cylinder head is suspected. This test confirms the presence of exhaust gases in the cooling system, but does not pinpoint the exact source of entry.

  • Page 107: Fuel Leak Test

    Vehicle Testing Procedures Fuel Leak Test The analyzer is extremely sensitive to fuel vapor, even at relatively low concentrations. Use this test to find leaks in fuel system components long before the liquid fuel is visible. Any part of the fuel system can develop leaks, but common leakage areas include: •...

  • Page 108: Exhaust Leak Test

    Vehicle Testing Procedures Exhaust Leak Test The analyzer is extremely sensitive to HC, even at relatively low concentrations. Therefore, it is useful for checking exhaust system components for leaks. A leak in the exhaust system can lower the HC, CO and CO readings at the tail pipe, while raising the O reading.

  • Page 109: Fumes In Passenger Compartment Test

    Vehicle Testing Procedures Fumes In Passenger Compartment Test When an exhaust leak into the passenger compartment is suspected, the vehicle should be tested immediately. Exposure to carbon monoxide gas can cause nausea, headaches, drowsiness and death in as little as 30 minutes. The cause of any exhaust fumes in the passenger compartment should be eliminated before operating the vehicle.

  • Page 110: No-Start Condition-Fuel Test

    Vehicle Testing Procedures No-Start Condition—Fuel Test A vehicle that cranks over but does not start, could be experiencing: • Mechanical engine problem, • Ignition system problem, or • Fuel delivery problem. Use the following test to help determine if the fuel supply system is the problem.

  • Page 111: Diagnostic Technique

    Diagnostic Technique Interpreting gas concentrations under a given set of conditions becomes a matter of: • Understanding engine operation and the system or systems under test, • Understanding the relationships of exhaust gas concentrations to each other, to the engine operation and to the catalytic converter, and •...
  • Page 112 Diagnostic Technique Lean Air-Fuel Ratio • Lambda is greater than 1.00. If Lambda = 1.10, this means 10% excess air compared with stoichiometric. • High HC is an indicator of excessive leanness and misfires. • O is a better indicator of leanness and misfires than HC. •...

  • Page 113: Air-Fuel Ratio Effects

    Diagnostic Technique Air-Fuel Ratio Effects Figure 7-1 contains some of the results possible when the air-fuel ratio is sustained at conditions ranging from too lean to too rich. CONDITION RESULTS Too Lean Poor engine power Misfiring at cruising speeds Burned valves Burned pistons Scored cylinders Spark knock or ping...

  • Page 114: Five Gas Combination Readings

    Diagnostic Technique Five Gas Combination Readings This chart lists some of the possible combinations of exhaust gas values and the most likely cause(s). Variables do not include secondary air. Legend: L = low; M = moderate; H = High Possible Problems / Conditions Thermostat or coolant sensor faulty.
  • Page 116 420 Barclay Blvd. Lincolnshire, Il 60069-3606 Tel: 847-478-0700 Fax: 847-478-7311 ZDGA1000 Rev B ©2001 Snap-on Tools Company Printed in U.S.A. (7/01)

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