1990 dakota, 3.9 auto 4x4 longbed. every damned morning when i go to leave for work at 5am the friggen truck refuses to start. the only way i can get it to start is if i turn the headlights on and off quickly while cranking and most of the time itll fire up, however if it idles a bit to warm up, it will randomly turn off. it does this when cold, in the morning when i go to work and again in the afternoon when i leave work, as well as any other time it sits and cools off. it has fuel all the time, it just loses spark. when its warm it fires right up. it stalls out when driving down the road as well, going along at speed and it will just cut out, sometimes itll come right back on, othertimes i have to crank it and hope for the best. ive replaced the cap, rotor, plugs, wires, ignition coil, tps sensor, and today the whole damned computer. map sensor seems to be working as it runs like crap and dies out when i unplug it, iac motor is working as it does change the idle speed, crank sensor?? i cant find the crank sensor anywhere on the truck, it says on here its on the pass side of the motor when the belhousing meets the motor but i cant see in there enough to tell. im sick and tired of screwing with this truck, its cold as hell at 5am and i just want the damned thing to start and get me to work!! its a 1990, so it dosnt have the stupid wire splice problem all the later models do. im out of ideas and tired of throwing parts at it. only sensor i can think is the crank sensor, but why would it be a cold/warm thing??? HELP!!!

 

just spent 40 mins looking all over where the motor meets the bellhousing. i see no wire connector or crank sensor anywhere. all i see is the main large connector for the transmission wiring. i cannot find any sensor or (according to all the pictures of the damned thing) any sensor held in with 2 bolts with a 3 wire plug. only thing i found was a melted spot on the o2 sensor wiring so i unplugged the sensor. before i changed the computer the maint required light was on. noticed earlier that it was no longer on. would the 02 sensor wiring somehow cause lost spark? im at a loss. this truck is pissing me off. im ready to light it on fire and watch it burn.

 

How on earth did you ever figure out how to start it this way? LOL

When I needed a new o2 sensor in mine, My truck would sometimes putt putt around when I put it in 1st gear and tried to go.. It did it every once in a while (maybe 1-3 times a day), as soon as I got the one I needed put in, it doesn't do it anymore. I don't think the actual oxygen sensor it's self has anything to do with the spark, but it does have a lot to do with the fuel. Did you replace both o2 sensors?

 

Found this concerning your '90 model 3.9. If it's a TBI, there is no crank pos. sensor

 

It always died when I turned the lights on lol. I'm going to replace the hall effect sensor today.