Tach and no communication issue

[Kasey]

I bought a 1998 Dodge ram 3500 with a 24 valve Cummins manual transmission 4x4 the problem is the ABS light flashes the entire time as soon as you turn the key on the wait to start takes a second to come on about 10 to 30 seconds when it does come on, it only comes on for about 3 seconds and then you hear the pump come on for maybe 2 seconds it is a aftermarket air dog pump it fires right up every time but my RPM gauge falls to zero after 10 seconds it has no loss of power or anything unusual after it falls to zero changed the crank sensor and checked all wiring and it is fine the PCM has been repaired and it will do this every time I can turn it off and turn it back on and it will do the exact same all gauges work but tach, I've checked all fuses and when I hook up a scan tool it will only communicate with the Cummins computer but I see rpm,tps,ect under live data I have bus voltage and I have tried unplugging every module except the engine computer to try and get communication and it will still not communicate when the RPM gauge falls to zero it sets the check engine light for the crank sensor but it has no other codes have any idea? It's a weird one lol

[dripley]

Your 98 has both a crank sensor and cam sensor. I cant remeber which one reads rpm for the gauge to display. Some one will come along that knows better than me. The WTS light stuff is pointing to an ECM problem. The other stuff is above my paygrade.

[Kasey]

Dripley from my understanding the crank is the gauge I have the 5v and ground but I don't have a way of checking the signal I'm hoping it's something simple knowing my luck it isn't and it has to do with the communication problem I'll unplug the abs and the light will go solid I've been all over prodemand and identifix trying to find something..

[dripley]

Do you have any trouble codes?

[Kasey]

8 hours ago, dripley said:

Do you have any trouble codes?

Just for the crank sensor after it quits working other than that no codes