Chapter 34 Advanced Diagnostics 683 Copyright by Goodheart-Willcox Co., Inc. • When an engine performance problem only occurs at a specific temperature, suspect electronic parts. To check a component for problems aff ected by temperature, use a heat gun to warm the component or a can of freeze spray to cool it. If the problem occurs with the tempera- ture change, the unit is at fault and should be replaced. • A dynamometer is used to measure an engine’s power output and performance. By loading the engine, the dynamometer can check engine acceleration, maxi- mum power output, and on-the-road performance characteristics. • A cranking balance test is done to check the engine’s mechanical condition. • A scan tool snapshot is an instantaneous reading of operating parameters. It is oft en taken when a problem is hard to fi nd or when intermittent troubles are present. • Scan tool datastream values are “live” electrical values measured with the vehicle running or driving. Th ey almost eliminate the need for a breakout box or pin- point measurements of electrical values. • A cylinder balance test, also called a power balance test, measures the power output from each of the engine’s cylinders. • Th e OBD II drive cycle is designed to tell the technician whether the OBD II system is operating properly. Th e drive cycle is normally performed when the battery or ECU has been disconnected or aft er diagnostic trouble codes have been erased. Additionally, some states require that the drive cycle be performed before an emis- sions test. Th e drive cycle is diff erent for each vehicle, so check the service manual for specifi c instructions. • An oscilloscope, oft en called a scope, displays voltages in relation to time. By comparing the scope pattern to a known good pattern, the technician can determine whether something is wrong in the circuit. Scope volt- age is shown along the vertical axis of the screen. Time is given on the horizontal axis of the screen. • An oscilloscope is oft en used to diagnose ignition sys- tem problems. Th e scope’s controls allow it to display both primary and secondary ignition system patterns. Th e primary scope pattern shows the low voltage changes in an ignition system. Th e secondary pattern shows the high voltages needed to fi re the spark plugs. • Th ere are four scope test patterns commonly used by the technician when checking ignition system opera- tion: primary superimposed, secondary superimposed, parade (display), and raster (stacked). • A scope ignition coil output test measures the maxi- mum available voltage produced by the ignition coil. A load test, or acceleration test, measures the spark plug fi ring voltages when engine speed is rapidly increased. • Four types of fuel injector circuits are saturated switch, PNP, peak-and-hold, Bosch peak-and-hold. • An exhaust gas analyzer measures the chemical content of the engine’s exhaust gases. With the engine running, the exhaust analyzer will sample, analyze, and indicate the amount of pollutants and other gases in the exhaust. Th e technician can use this information to determine the condition of the engine and other systems aff ecting emissions. • Th ere are three diff erent types of exhaust gas analyz- ers: two-gas analyzers, four-gas analyzers, and fi ve-gas analyzers. Th e two-gas exhaust analyzer can measure the amount of hydrocarbons and carbon monoxide in a vehicle's exhaust system. Th e four-gas exhaust analyzer measures the quantity of hydrocarbons, carbon monox- ide, carbon dioxide, and oxygen in an engine’s exhaust. Th e fi ve-gas exhaust analyzer will measure hydrocar- bons, carbon monoxide, carbon dioxide, oxygen, and oxides of nitrogen. Review Questions—Chapter 34 Answer the following questions using the information provided in this chapter. 1. _____-_____ diagnostics involves using a consistent, logical procedure for narrowing down the possible problem sources. 2. What fi ve basic steps are involved in strategy-based diagnostics? 3. _____ _____ results from induced voltage into wires and can cause a computer to malfunction. 4. List six things you can check with a digital thermometer. 5. Explain how to check for temperature-related problems. 6. When might a dynamometer come in handy during advanced diagnostics? 7. What is a scan tool snapshot? 8. When should the scan tool snapshot feature be used? 9. How can you use scan tool datastream values? 10. On a scope screen _____ is shown on the vertical axis and _____ is shown on the horizontal axis. 11. Summarize how to use a scope to test computer system sensors. 12. With the engine cranking, a magnetic sensor should commonly produce _____ volts peak-to-peak. (A) 0.5 (B) 5 (C) 1.5 (D) 15 13. How do you scope test a knock sensor? 14. Which section of a secondary ignition scope pattern will indicate problems with the ignition coil or coil pack? 15. Which section of a secondary ignition scope pattern will pinpoint problems with the spark plugs, the plug wires, the distributor rotor, and the distributor cap?