Got a P1693 code when I checked computer diagnostic through cycling the ignition three times. No other codes come up. Tach will sometimes cut off, falling to zero while driving, then coming back on a few minutes later. any ideas? Thanks

 

That is a generic code telling you another one has been set and stored you will need an obdII style reader to get it.

Not knowing what year your truck is look for a bad ESS at the front of the engine above the balancer on a 12 valve or the crank sensor or cam sensor on a 24 valve.

Could also be a wiring/connection on any of them.

 

what truck? On mine it was the crank sensor

 

Oops, forgot to mention that it was a 2001. 24valve

 

If I remember right the early 2001's still had the sensor behind the starter pointed at the crank.
The later 2001's (2001.5) the sensor is on the back side of the front cover just under the VP44 injection pump. Thats where mine is. Kinda of a pain to get to but its not the end of the world.
IF yours is behind the starter you will need to remove the starter to install the new sensor.
I would reccomend replacing the sensor with a Cummins part, and not one from the neighborhood parts house. Hope this helps..

 

Had the same problem. Bad crank sensor. Located behind the starter. Takes a little finesse to get the old one out sometimes. But not a big deal.

 

I second the Cummins part. I went through 2 in a year from the local parts store. 2 years and the cummins is still rockin

 

mine doesn't have a sensor behind the starter,it's under the vp44..........my truck is a early '01 (July 2000) my service manual confirms the location of the cam sensor...........