680 Auto Electricity and Electronics Copyright by Goodheart-Willcox Co., Inc. Note: Injector waveforms can vary slightly. However, the information provided in this text can help you analyze any ECU and injector trace. Refer to known good injector patterns if in doubt. Dual channel scopes will let you superimpose voltage and current traces for comparison. Th is simplifi es analysis since a problem with an injector or its supply wiring will only show up on the faulty circuit and injector. If on and off times from the stacked waveforms do not line up, you might have a sluggish or sticking injector. A sharp vertical rise in current means the injector is shorted. Th e Bosch peak-and-hold injector waveform is similar to the peak-and-hold waveform except that instead of lower- ing the current to hold open the injector, current is rapidly pulsed on and off . See Figure 34-38. Exhaust Gas Analyzer An exhaust gas analyzer is a test instrument that mea- sures the chemical content of the engine’s exhaust gases. Some advanced scan tools can be connected to an exhaust gas analyzer module to read the contents of a vehicle’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 infor- mation to determine the condition of the engine and other systems aff ecting emissions. An exhaust gas analyzer is an excellent diagnostic tool that will indicate excessive emis- sions caused by: • Fuel metering problems. • Engine mechanical problems. • Vacuum leaks. • Ignition system problems. • PCV troubles. • Clogged air fi lter. • Faulty air injection system. • Evaporative emissions control system problems. • Computer control system troubles. • Catalytic converter condition. Types of Exhaust Gas Analyzers Th ere are three diff erent kinds of exhaust gas analyzers: two-gas analyzers, four-gas analyzers, and fi ve-gas analyzers. Th e two-gas exhaust analyzer can measure the amount of hydrocarbons (HC) and carbon monoxide (CO) in a vehicle’s exhaust system. Although this analyzer has been used for a number of years, it cannot accurately ana- lyze the exhaust gases from newer engines. Th erefore, it is being replaced by the four-gas analyzer. Th e four-gas exhaust analyzer measures the quantity of hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO 2 ), and oxygen (O 2 ), in an engine’s exhaust. Most state air quality agencies use the four-gas analyzer. Although carbon dioxide and oxygen are not toxic emissions, they provide useful data about the engine’s oper- ating effi ciency. Late-model engines are so effi cient that a four-gas exhaust analyzer is needed to accurately evaluate the makeup of the exhaust gases. It provides extra informa- tion for diagnosing problems and making adjustments. Th e fi ve-gas exhaust analyzer measures hydrocarbons, carbon monoxide, carbon dioxide, oxygen, and oxides of nitro- gen. It is the most modern and informative type of exhaust gas analyzer. Oxides of nitrogen are a toxic pollutant that should be measured, if possible, as a means of diagnosis. Using an Exhaust Gas Analyzer To use an exhaust gas analyzer, plug its electrical cord into a wall outlet and then power it on. Allow it to warm up as described by the manufacturer. Aft er warm-up, zero and calibrate the analyzer. Exhaust gas analyzer calibration involves zero- ing the meter scales while sampling clean air (no exhaust gases present in room) with the analyzer. Newer analyzers sample a calibration gas (mixture of several gases) to adjust the meter readings for accuracy. Th e gas is automatically metered while the meter scales are calibrated. In most cases, any calibration adjustment is done automatically by the analyzer when commanded by the technician. Older ana- lyzers may have to be manually adjusted. Warning: Never inhale exhaust analyzer calibration gas. The gas contains emission gases that can be harmful to your health. Before testing the vehicle, take it on a thorough road test. Th is allows the vehicle to reach the proper operating temperature. Never test a vehicle with a cold engine, as inaccurate readings will result. To begin the test, install the probe in the vehicle’s tailpipe. If working in an enclosed shop, slide the probe through a hole in the shop’s vent hose, Figure 34-38. Bosch peak-and-hold fuel injector waveform. Time Injector On Time ECU Opens Circuit Pulsed On and Off Inductive Voltage Spike ECU Grounds Circuit ECU Switches to Current Limiting Circuit Voltage