Tach - 12V Cummins w/ Dakota Digital
 

I have a 55 Chevy truck w/ 12V diesel conversion. I have the engine running with the PCM. I have a Dakota Digital HVX dash and a Digital Gaurd Dawg keyless ignition. It all works great with one exception - I can't get an immediate tach signal that the tachometer or ignition will recognize. The alternator has a "W terminal" and it does drive the tach (and presuamable the ignition) but there is some lag before the tach actually responds unless you rev the engine. I tried tying the tach output from the PCM to the ignition box and the Dakota interface, but it reads nothing. I even tried with the DD diesel tach interface - nothing. The LED indicator on the tach inteface doesn't even flash so I'm either getting nothing into the PCM, or nothing out that the dash or ignition will recognize. Any recommendations on how to confirm the ESS sensor is working? What is the correct spacing between the damper and sensor? Will the ESS sensor voltage swing enough to drive the tach (or tach interface) by itself? Is it normal for an alternator tach out signal be slow to develop (like maybe it takes the alternator field a while to excite and start putting out?)
FYI - this lag time without a tach signal if causing the ignition box to keep the starter engaged too long, and causes the remote start feature to attempt 3 times to start the engine (all while it's already running!!). With all of this going on, I hate to keep on trying different things - it has to be hell on the starter and flexplate!)

The alt probably isn't being energized right off the bat... is your volts gauge reading low at the same time the tach doesn't read?

The stock crank sensor signal is 2 pulses per rev. I run an isspro 3" tach off the factory tach harness connector (92-93). The tach has dip switches that you set for 2 pulse signal. It is a little fluttery though. A higher pulse-per-rev would probably solve that.

Where are you installing the DD diesel tach pickup? Is it close enough to read the flywheel teeth?

Isspro also makes a tach pickup kit you install on the crank damper

https://www.dieselpowerproducts.com/...ensor-kit.aspx