M923A2 Tachometer Question:

[Defcon-1]

I have a problem with my Tach, both the RPM indication *and* the Hobbs Meter don't work. Looking in the TM I see that there is a "Tachometer Pulse Sensor" that is right behind the gauge. Does that drive both functions of "RPM" and "Engine Hours"? I'm trying to best troubleshoot the parts before ordering anything, just want to make sure I go for the best component first.

In the TM, looks like in the system there is only:
- Tachometer Drive Cable
- Tachometer Pulse Sensor
- Electrical Connection(s)
- Tachometer Gauge

Once I get access to the pulse sensor, I should be able to eliminate the electrical portion being the issue by checking with a meter on the connector. I could also disconnect the Drive Cable from the sensor and run the engine to see if that's working, to eliminate the cable from being the issue. Just not sure how the Pulse Sensor comes into play with both the RPM and Engine Hours functions. If it does both, I'm leaning toward changing the sensor first. If it only does one, (for example, RPM indication only), I know my Tach Gauge is most likely the problem. I just can't find much information on the Pulse Sensor. Any ideas Gents?

Ty kindly,

 

[M35A2-AZ]

The Pulse Sensor is used for the diagnostic plug under the dash on the right side. You can remove it if you want.

 

[Jbulach]

Check the drive cable before you replace anything.

 

[Defcon-1]

Check the drive cable before you replace anything.

You think I should fuss with it where it attaches to the front of the engine? Or just disconnect it from the Tach end to see if it's actually rotating?

 

[Jbulach]

I haven’t messed with them on these trucks, but on other equipment the ends tend to break off, usually on the engine side. However, I would start at the tack end if possible to see if it’s turning.

 

[Defcon-1]

I haven’t messed with them on these trucks, but on other equipment the ends tend to break off, usually on the engine side. However, I would start at the tack end if possible to see if it’s turning.

Sounds good, will report back with findings, ty!