Got another head scratcher that hopefully some fresh eyes can help with.

Truck is a 2WD 2001 4.7 Dakota and over the last few months has begun to act very strange.

While idling, in Park,Neutral,or Drive, the RPMs surge briefly before dying. The swings can be pretty substantial but once it dips below aprox. 400 RPMs the truck will just die. It will always start back up immediately and the only way I've been able to combat this is by revving the engine and holding it.

The truck also power surges? while driving. I've experienced it at speeds from 30 mph up to 75 mph. It feels like a sharp complete loss of power and will happen sharply while maintaining driving speed, not accelerating.

And the last symptom is the truck will die unexpectedly while driving. Is usually happens when sitting at a red light or coasting but I have experienced it with the truck in reverse. Sometimes the truck just shuts off and I don't even realize it until I try to move the steering wheel, other times the RPMs will fluctuate about 300 RPMS moments before it happens. Radio stays on and so does everything else in the interior. It will start on the first try every time after doing this.

So the part that makes this hard for me to diagnose is the Check Engine Light has never came on and no codes are present when hooked up to a scanner. The problem is intermittent but happens about once every couple days.


Here is what I have done so far.

Drained transmission and replaced both filters
Removed and cleaned the throttle body
Air filter
PCV Valve
Idle Air Controller has been swapped with 2 different used OEM sensors. (Both sensors were cleaned)

Replaced the following sensors with new aftermarket sensors.
Camshaft Position Sensor TWICE
Crankshaft Position Sensor
Throttle Position Sensor

Any suggestions would be greatly appreciated.

 

What does a manual sweep of the TPS show for readings? Is there a dead zone at idle or around 40%/cruising throttle position?

 

Try unplugging the O² sensors upstream and down of converter. I had a similar problem last year. Typically it would run fine but it would bog down sometimes when idling or just maintaining speed. I'd have to goose it to prevent stall. Unplug o2 sensors and hasn't happened since. My converter was removed by a previous owner so I don't really have to worry about it getting trashed by fuel. I will probably still replace the sensors eventually but I'm not pressed about it. I did a lot of research trying to figure out my issue and I read that if the pcm isn't getting a reading from the o2 sensors then it will revert to factory fuel trim settings. I've heard that eventually it could go into a fail safe mode but mine hasn't show any signs yet. That's why I will probably replace the sensors when I get around to it. You could probably just pull the o2 sensor fuses in the fuse box under the hood fyi. I just explained the route I took. I dealt with this problem for probably 9 months and it was very frustrating. Once I figured it out it was a new truck to me.

 

Yep 02 can cause all kinds of issues ESPECIALLY after market non OEM.
Same with many other non OEM sensors .
Fuel trim can be impacted too.

 

UPDATE:

So as of right now the truck is running fine on my daily commute to work. I haven't had the time to take it on a proper long drive yet to see if the problems are really gone, my daily drive is about 20 minutes one way. Over the last weekend I replaced the PCV Valve just because its cheap and hasn't been done in a while. I disconnected one of the downstream o2 sensors just to look at it and it looked pretty burned up but have not actually replaced any o2 sensors yet. I replaced the crankshaft position sensor. Also I made sure to disconnect the battery during all this to reset the PCM again. Everything was done on Saturday and seemed to stop the lurching/hunting while driving but the truck stalled twice right before I put it in the garage after a 45 minute test drive. So on Sunday I Seafoamed the intake after getting the truck properly warmed up. After letting it sit for about 20 minutes I ran the **** out of it with a moderate cloud of white smoke behind me the entire way. Only strange thing I noted was that the truck seemed to shutter at 3000 RPMs once at the end of the street. After doing that everything seems to be fine. I've been driving for over 1 week now with no issues. It seems to idle better now as well.

Attached are pictures of the old and new crankshaft position sensors. Are markings like this normal? The old sensor was less than 4 years old. The picture of the new sensor was taken before installation or use.

 

Looks like the sensor might be a bit too close to the flexplate.....