I need help!! Crank Sensor or something else?
 

I have a 1996 Dodge Ram 1500, 5.9L gas, 2wd with just over 200 k. I purchased the truck a little over a year ago from my father in law knowing the truck has a issue. I thought it was bound to be a simple fix. Boy, was I wrong! My truck will absolutely run fine for about 3 days at a time. On or about the 3rd-4th day it will start shifting bad, shimmying, bucking and shut off like someone just turned they key. The truck will periodically throw a P1391 every once in a while, but not all the time. The problem seemed to start not longer after the transmission had been removed, rebuilt and re-installed. The fuel pump assembly has been replaced(a year or 2 ago), multiple cranks shaft sensors (over the past 2 years), replaced the "Pick Up" coil under the distributor cap, distributor cap, rotor, fuel line, fuel filter, battery and coil. Same issue persists. Sometime's it will not start for 5 minutes up to about 2 weeks, then bust off and purr like nothing ever happened. The truck does not seem to have spark in these no start conditions. Fuel seems to be pumping great. I have taken to multiple mechanics in my area. They all say the same thing, that there is nothing wrong with the truck. The truck performs fine when they attempt to diagnose problems and end up telling me that they cant find anything wrong and for me to come pick it up. The last time I drove it to work and back I smelled something getting hot, but was unable to drive it the next day due to acting up when I pulled out of the driveway. I have read that these models will not keep a parts house crank sensor and they need a mopar sensor to run right. I can not find a mopar sensor for the automatic model, only the standard transmission models. Is Delphi the oem crank sensor for automatic versions of this model? I have tested the crank sensor in the truck and it have the correct voltage to it? Any ideas? Please help! Could a faulty ignition switch do this? Also, what if the timing chain had slack? I am not sure timing would allow the truck to run perfectly and all of a sudden not?

What brand crank sensors are you using? The lack of spark indicates that the problem lies somewhere in the ignition system...... Next time it fails to start, verify you have power to the coil when you first turn the key on, (only lasts about three seconds...) if that's ok, put a test light across the terminals on the coil connector, (with it unplugged, much easier,) and see if the PCM is actually triggering the coil. (may be a bad PCM....)

If my memory serves me correctly, I tested power to and from the coil and it was good during the last no start situation. As for the brand of crank sensor I have been using, I believe they have been Borg-Werner or Delphi. I will have to dig up a box or receipt to be sure. I appreciate any further insight.

PCM breaks the ground circuit to fire the coil. If it isn't pulsing, then that isn't happening. Either the PCM isn't getting the clue that is should be doing so, or, it thinks it is.... but that part is non-functional.

Also when it does run, going down the road, occasionally it seems like it will shut of for a split second multiple times. It is barely noticeable. Feels like when you are on the interstate and there are cracks in the pavement, almost like a barely noticeable surge. I want to say this happens when the trouble is about to start. Hopefully I will be able to give it another look over today, weather permitting. Would a failing ASD have these symptoms? Also wondering about a ignition switch? If it is something that could be replaced, I wish it would just go out for good. Troubleshooting a intermittent issue is for the birds.

Just to be sure I am on the same page as you. The crankshaft sensor should send a signal to the PCM and in return the PCM send a firing signal to the coil correct?

You are correct sir! :D

Given the intermittent nature of your issue though.... I think that one is gonna be fun to find and fix.

I can confirmed that I have been replacing the crank sensor with the Borg-Warner brand ($76.00). I found a Delphi ($115.00) here locally at NAPA and will be able to pick one up tomorrow. If this fixes my problem, it will be well worth the price difference. I have drove the truck short distances a few times today and it has been running fine so far. I know from my experience to not get my hopes up, but it runs better and more power than my late model Silverdo. Not looking forward to the sensor swap out!

As an FYI, I got a CPS from the stealership for $80... they're Delphi (I believe).

I had a similar issue. It was the crank sensor. Stay clear of Borg warner! Put one in and less than a year it craped out. You should be able to get a Delphi for around $60 on rockauto if i recall.