I own a 1997 Dodge Ram 1500 4x4 with a 5.9. I was having an issue where my truck would only run on my stock OEM crank sensor. I was buying new sensors because I was losing my sync between the crank and the cam on my scan tool. And the symptoms I had were, truck sometimes stalling at idle, sometimes just an rpm drop, and sometimes it would buck while driving like it was losing fuel pressure. No check engine light. You would think crank sensor but my truck WOULD NOT RUN on aftermarket crank sensors. Well it turns out it's because the PCM was bad. Normally you would think a PCM wouldn't really affect if an aftermarket or OEM crank sensor works on your vehicle but that was my situation. And that's what happened with my truck. I chased the problem for 6 month until I finally figured it out myself today.


I wanted to make this post so if someone had a similar situation, they can easily refer to this through a google search or searching the forums. I now have an aftermarket crank sensor installed with a used PCM from a different 97 5.9 and everything runs perfect. It's was a mind boggler. And I just wanted to share this knowledge to others who may run into this in the future.

 

I have one in our shop doing exactly what you experienced, but, this one has to get warmed up before it acts up.

 

Open loop and closed loop idle. I think the O2 sensor is a good candidate when its warmed up as it is not used when started up. But, you can look at closed loop vs open loop idle operation in the repair book and it list components.