tach pulsating
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From: Pennsylvania
tach pulsating
My tach just started pulsating when I apply the brake pedal. idles at 800 in drive in neutral with brake on it idles pulsates between 800 to 850 2001 Dodge Ram ( auto) all stock but exhaust
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Joined: Nov 2003
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From: League City, TX
What you guys are describing sounds a lot like the "bouncy tach needle". If the needle is simply bouncing a little, but there is no audible change in the sound of the engine, and it is running smooth, then you have nothing to worry about.
The CPS (cam or crankshaft position sensor) senses the RPM's. The output of that goes to the ECM, which in turn feeds the tach. Essentially, its an analog signal that gets converted to a digital signal (in the ECM) and then changed to whatever the actual guage requires. Also the sensor itself is a magnetic sensor, attached to the crank (or cam) shaft is a magnet that creates a pulse in the sensor as it swings around.
A lot of 24V engines have the bouncy needle, including mine. Just the nature of the 24V.
The CPS (cam or crankshaft position sensor) senses the RPM's. The output of that goes to the ECM, which in turn feeds the tach. Essentially, its an analog signal that gets converted to a digital signal (in the ECM) and then changed to whatever the actual guage requires. Also the sensor itself is a magnetic sensor, attached to the crank (or cam) shaft is a magnet that creates a pulse in the sensor as it swings around.
A lot of 24V engines have the bouncy needle, including mine. Just the nature of the 24V.
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