KANTANKRUS Posted May 31, 2021 Share Posted May 31, 2021 Clueless, thats why I am asking. How does a tachometer read the RPMs of a motor? Do our trucks have a cable to attach too something? (If so) What? My 87, 4x4, AX15, 4.0 liter, does not have a tachometer within its instrument cluster. Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 31, 2021 Share Posted May 31, 2021 From my understanding from the FSM, the tach reads pulses sent from the coil from when it fires. Link to comment Share on other sites More sharing options...
KANTANKRUS Posted May 31, 2021 Author Share Posted May 31, 2021 59 minutes ago, eaglescout526 said: From my understanding from the FSM, the tach reads pulses sent from the coil from when it fires. What is the FSM? Link to comment Share on other sites More sharing options...
eaglescout526 Posted May 31, 2021 Share Posted May 31, 2021 Factory Service Manual. Link to comment Share on other sites More sharing options...
scaleless Posted May 31, 2021 Share Posted May 31, 2021 9 minutes ago, RestoringNV said: What is the FSM? Factory service manual. The ICM generates a PWM signal which is filtered to a constant voltage by the tachometer. The signal gets to the guage cluster regardless of if it has a tach or not. The tach is pulled towards zero by a permanent magnet, and the voltage from the ICM energizes an electromagnet that pulls the needle away from zero. The balance between the permanent magnet and the electromagnet is what controls the needle position. Link to comment Share on other sites More sharing options...
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