Hello, new to posting on this website, but have done tons of research with you guys and you’ve already helped me out a few times. However, i’m experiencing a problem I haven’t really been able to find, my truck runs beautiful, idles beautiful, but somehow only for about 20 miles. It develops a light hesitation/jerking exactly at 20 miles every time. This problem is temperature related as it does run normal again after cooling down.
After the hesitation starts, it doesn't cut any fuel/spark, I’m able to limp it home if I please. We’ve replaced lots of things we’ve thought could be the problem (fuel pump, TPS, Crank shaft sensor, ignition coil-cap-and rotor, purge valve, idle air control valve, also the battery). I also blew up the front main seal on it pulling 60 bales of alfalfa, so we found trans fluid was soaking the crank sensor, still wasn’t the problem😑. We’ve thrown the parts we haven’t normally replaced in a maintenance at it because of the sentimental value we have in the truck, we figured it might need it anyways.
I have a remanufactured PCM on the way but I just thought I’d get any additional insight before that comes in. My father and I have done A LOT of work on this truck including rebuilding the trans, full paint-job, and lots more, we love the truck.🤣🤣 Thanks in advance.

 

Disconnect the front O2 sensors (if you have more than one....) and go for a drive. See if the problem goes away.

Welcome to DF!

 

Thank you!
Completely forgot to mention that, I figured the O2 sensors would really affect the truck if it had cats, could I be wrong on this assumption? Love the loud noises…🤣

 

Also forgot to mention, everytime I force the problem to occur (just by test driving after every newly installed part) the PCM is very hot, hotter than the radiator, enough to burn our fingers, and i’m talking about a 30 minute drive. Still idles perfectly, but the rpm’s seem to stick, anywhere between 1250-1750. after about 15 minutes of idle with that, the sticking then goes away…. this has had EVERYBODY confused. I’ve only ever had one CEL pop up, but I am unable to read the stored codes because the OBD2 doesn't work, so key-on, key-off method gave me the Evap purge valve, which was very full of charcoal. Temp and oil pressure gauges are also shot, something has always just screamed out PCM to me.

 

For the front O2 sensors, cats don't matter. For the rear O2 sensors, that measure cat efficiency, they do matter.

The PCM getting too hot to touch though, that is concerning.....

 

Definitely, so I figured the truck has 250k miles already, and I’m willing to bet it’s the original PCM, so I figured I could use a backup anyways. I might as well order some new O2’s hearing that news though!

 

We were considering the ASD relay is being tripped by the PCM to protect something from overheating. We also found the trans cooler lines were up against the manifold, but haven’t been there long enough to effect the lines themselves…. So many ideas.😭

 

NTK or Denso O2 sensors ONLY please. These trucks don't play nice with Bosch.

 

Happy Thanksgiving!

Thank you for the help for the time being-I will update you after the PCM comes in on the 2nd, along with the source I got it from, if all is well with it. I still use the truck for dump runs as it’s right down the street, i’m only able to really test it when there isn’t a ton of construction waste in the back of it🤣. Right now the PCM is my main concern as it’s hotter than hot, if the problem remains I will be going after the o2’s/ASD relay, there really isn’t any more parts🤦🏽‍♂️ My 99 Dakota with a 3.9 is just not as fun🤣

 

Update: Sorry for the late reply, way too busy with work. I actually got the PCM early, dropped it in the night of to make sure all was well and it still started… Flashmasters from Ebay was very helpful, the PCM worked fantastic, however I still have the same issues. We were able to get to the cooler lines and move them over, but we somehow previously cross threaded the fitting, stripping the threads, and we had to replace it with a parts trans I “conveniently” had laying around… around 15 miles into the test drive, all the trans fluid dropped out. I was about 6 miles from home without 1st, 2nd, and OD, no big deal, we’re familiar with the transmissions. As I was pulling into my neighborhood, the original problem then came in 🤦🏽‍♂️. PCM was good the entire time, although I completely forgot to check for temperature of the new PCM after this drive, I also ended up switching the ASD, with the starter relay ruling that out as well. Would you happen to have anymore information about the O2’s, as far as the truck being catless? Or anything else I could possibly check into? Would be pretty easy if I could just read the O2 readings, but this is the only vehicle my cheap scanner won’t work with🤣 The truck ran beautiful for that 15 miles though🙃