To test for a tach signal or injector pulse, to which measurement setting do you set the DMM?

To test for a tach signal or injector pulse, the appropriate measurement setting for the Digital Multimeter (DMM) is AC Volts/Hz. This setting is designed to capture the alternating current signals associated with the operation of ignition systems and fuel injectors, which typically produce pulses rather than steady DC voltages.

When measuring a tach signal, which indicates the engine's RPM, the output is often a square wave or similar pulse, generated by the ignition system or cam/crank sensors. The DMM set to AC Volts/Hz can read these fluctuating signals, providing information on the frequency and amplitude of the signal, which correlates directly to engine RPM.

In contrast, the DC Volts setting would be used to measure steady state voltage levels, which may not accurately reflect the rapid changes in voltage associated with pulses from the tach signal or injector. The Ohms setting is relevant for measuring resistance in circuits, and the Continuity setting is primarily used to check if a complete circuit path exists, neither of which would provide the necessary data for tach or injector pulse measurements.