Engine/Transmission (1994 - 1998) Tachometer problems

[skip1996]

I hope this is a easy one. My low mileage '96 w/307k miles has a spastic tach. It jumps all over the place. Is this a sensor problem? Or? Skip

 

[GAmes]

Double check the spacing from the damper, it should be .050 + or - .001. Check the connector for corrosion, clean as necessary. Also check all the wire harness for a hole that might be rubbed through the insulation. Lastly, it could be the engine speed sensor has finally died. More than likely yours takes this connector http://www.genosgarage.com/product/sensor-3924432/electrical-sensors-2 but it might be this one. http://www.genosgarage.com/product/sensor-3923129/electrical-sensors-2

 

[Missouri Mule]

Could be the Tach gauge. If the tach gets down to zero the engine should die ( I think) if the engine speed sensor is acting up. If it is the guage it will keep running.

My tach is all over the place on my Moose (Freightliner). But hasn't set the check engine light on and the engine isn't revving.

 

[Missouri Mule]

As per 96 factory service manual.
The tach module in the instrument cluster operates the tach.
The powertrain control module (pcm) supplies the signal for the tach on circuit G21. Circuit G21 connects to cavity C31 of the PCM.
G21 is grey/light blue wire.(runs fron tach to pcm).

Engine speed sensor = 5 volt supply violet/white, crank position sensor signal (ess)grey/black, sensor ground black/light blue.
Engine speed sensor connections to PCM, ground a4,signal a8, power a17.

Hope this helps.