Buckshotram

The tach will be working then it will go out then come back on. It did this a week ago for about 45seconds now it goes back to zero then back to working off and on all day. Also when ever the tach quits the charge/battery guage will drop. Any ideas on what is going on its like I have a short.

jrs_dodge_diesel

Nope, your CPS (cam or crankshaft position sensor) is going dead. That sensor is where the tach gets its signal, it also tells the ECM that the engine is running. The ECM also controls the A/C clutch and the alternator output. When the ECM sees the loss of signal from the CPS it think the engine has been turned off and turns off the A/C clutch (if it was on) and the alternator.

Buckshotram

is that someting that I can change?

jrs_dodge_diesel

Yep, Sepending on where its located might make it more difficult. One spot for it was right at the harmonic balancer on the front of the engine. There other place for it was mounted in the drivers side in the block behind the starter. I believe that once you get to it and find it that all thats needed to remove is 1 or 2 bolts and an electrical connector.

Buckshotram

Is this the sensor on the harmonic ballancer that I removed doing the kdp and set back up to with a feeler guage i think .049-.051` is it.

J BODY

That would be the one buck.

Buckshotram

Thank you for your help.

infidel

12 valves don't have a crankshaft position sensor (CPS).
The sensor that is giving you trouble is the engine speed sensor (ESS) located at the harmonic balancer.

Buckshotram

Any body know how much one is? Advanceautoparts.com has a crankshaft position sensor that is $50 for automatic. Would I be bettor off with a factory or cummins replacement?