Two technicians are discussing how to check fuel injector resistance. Technician A says that you would use a
digital ohmmeter read in tenths of an ohm to measure the resistance across the injector terminals. Technician B
says that the resistance of the injectors should be measured twice-once when the engine and injectors are cold,
and once after the engine has reached normal operating temperature. Who is correct?
A. Technician A
B. Technician B
C. Neither Technician A nor B
D. Both Technicians A and B
The Correct Answer and Explanation is :
Answer: D. Both Technicians A and B
Both Technician A and Technician B provide correct information regarding the checking of fuel injector resistance.
Technician A states that a digital ohmmeter should be used to measure the resistance across the injector terminals. This is accurate because an ohmmeter is the appropriate tool for checking electrical resistance. When measuring the resistance of fuel injectors, it is crucial to use a digital multimeter (DMM) set to the ohm setting, and a resolution of tenths of an ohm is appropriate since it allows for precise measurements. Fuel injectors typically have a resistance ranging from 12 to 16 ohms, and precise measurements can help diagnose issues like short circuits or open circuits.
Technician B emphasizes the importance of measuring the resistance twice: once when the engine and injectors are cold, and again after the engine has reached normal operating temperature. This is also correct. The resistance of a fuel injector can change with temperature. Cold resistance values can differ from those measured when the injector is hot due to the thermal characteristics of the materials used in the injector. By taking measurements at both temperatures, a technician can better assess the injector’s condition. A significant difference in resistance values may indicate a problem with the injector, such as degradation or failure of its components.
In summary, both technicians provide valid information that is critical for accurately diagnosing fuel injectors. Using a digital ohmmeter to measure resistance and considering the effects of temperature on those measurements are essential practices in automotive diagnostics. This dual approach allows for a more thorough evaluation of injector health, ensuring that any issues can be identified and addressed promptly.