I have 2 Dakotas, I just bought a 1990 4x4, 3.9- has some strange problems. The man told me before I bought it, got a gremlin, I went ahead so here I am. Runs fine at start it upmost of time, suddnely I get in start it and runs rough and spits black smoke. It has a new computer and air sensor. Unfortunately I hear a occasional clank in the tranny or transfer case when in park or neutral, it stops when in gear and runs pretty good when in gear. Really odd, I also have the check engine light on, the previuos owner saya the problems started when the light came on, I checked the codes and they don't make sense.

I just thought I would see if this sound familiar, its a darn good looking truck, I mean yaaaa,,,

 

It seems to be in your ignition circuit, not sure, but maybe the ecu or ecm or whatever controls the firing at distribution. I had a chevy 305 that stopped when it wanted to and did all the things you say this is doing and it was my ecu in my distributor. I installed a v6 s10 module in the 305 v8 distributor and it ran very well since.

 

you're going to have to post codes to get any help with this. go over to the dakota section and post there, they'll be able to help you out a lot more.

welcome to DF!