I realize it is a longshot, but since the 1998 Durango is a supported vehicle, I was curious if anyone has experience with how the tach is driven? The manual seems to indicate it is driven by the crank sensor via the CCD bus. I am installing a Gen 3 LS V8, and have used an adjustable ratio tach signal adapter to reduce the GM 24 PPR crank sensor to the 8 PPR the Dodge generates. The GM sensor runs on 12V while the Dodge runs on 5V. The truck runs dual VCMs and the other gauges driven by the CCD bus work OK with the Dodge sensors adapted to the GM engine. This adapter alone did not power the tach, so I also hooked up the 1 PPR cam sensor. Using a dual step up/step down sine to square wave adapter on the crank signal, I got the needle to move, but the reading is too high and the needle is jumpy. Adjusting the input ratio so far has not made a significant difference.

Any info on how this engine drives the tach is welcome.