Chapter 34 Advanced Diagnostics 661 Copyright by Goodheart-Willcox Co., Inc. Caution: Do not apply too much heat to an electronic module. Excessive heat can damage components. Only match the engine operating temperature of about 200°F (93°C). Use a digital thermometer to monitor the temperature when heating the unit. Finding Moisture-Related Problems Symptoms that occur only when it is raining or snow- ing may be caused by moisture coming in contact with electronic components and wiring. To check if engine performance is aff ected or trouble codes are set because of moisture, spray engine components with a spray bottle fi lled with water. Using a Dynamometer A dynamometer, oft en referred to as a dyno, is used to measure an engine’s power output and performance. By loading the engine, the dynamometer can check engine acceleration, maximum power output, and on-the-road performance characteristics. Figure 34-7 shows a chassis dynamometer. If you are having trouble fi nding a driveability prob- lem, you might perform diagnostic tests while operating the vehicle on a dynamometer. Th is will let you simulate any condition that causes the problem. For example, you could connect a fi ve-gas exhaust analyzer to the tailpipe and operate the vehicle under load on the dynamometer, Figure 34-8. You can also shift the vehicle through each gear, accelerate to the speed at which the problem occurs, walk around the vehicle to listen for abnormal noises, or connect listening devices—all while simulating driving conditions. Figure 34-6. When intermittent engine problems appear to be caused by heat, cold, or a period of engine operation, suspect the electronic control circuits in the ECM. A—Freeze spraying directly onto the ECM may solve the engine performance problem. If it does, replace the ECM. B—If the engine stops running when air from the heat gun is directed onto the ECM, you have found the problem source. Do not overheat the ECM, however, or you could damage it. A B Freeze Spray ECM Heat Gun ECM Figure 34-7. A chassis dynamometer measures engine power output under road conditions. It can also load the engine while other tests are performed. (Sun Electric Corporation) Dyno Rollers for Car's Drive Wheels Figure 34-8. A five-gas analyzer is often used to check the con- tent of engine exhaust gases. This will give added information for finding the source of a performance problem when operat- ing a vehicle on a dynamometer.