New to forum so hello. Have a big problem, so i will give you a lot of detail, in hopes that someone can point me in a good direction. mechanically inclined, not so much with troubleshooting. I have 05 dodge cummins automatic 2500. 4 dealerships, 1 tranny shop into it with no resolution.
Known: before issue, my truck would shift into final drivegear at 50mph consistanly. If i coasted down to a slower speed, tach would fall slightly with speed until 45mph, then it would really drop off to an idle, until i used accelerator again.
Issue encountered: while on roadtrip to indy GP from richmond va, noticed tach having 200rpm jumps. Stopped at dealer in WVA, they diagnosed it, indicative of throttle position sensor (apps?), but safe to drive on. Cruise seemed to filter problem out a little. Dealer in INDY changed sensor, called it good. Drove truck, still had issue, they changed a shaft speed sensor, and it was good for about 100 miles, then started acting up again. Drove it home, another dealer... They changed both batteries saying it was a voltage issue, and called it good. 50 yards out of that parking lot I knew they sucked ( I told them what i was experiencing, they never drove to find out obviously and wasted 2 weeks for changing two batteries). Engine speed shifts back n forth while truck speed is anywhere between 48 and 72 mph. above 72... she runs normal, same with below 45. Also in the 48-72 range, if i let off accelerator, tach drops off like it used to at 45mph, but now it does it as soon as i get off it, regardless of speed. Also, the rpm jumps are more than 200rpm, at 70mph, im usually about 2200rpm, Ive had it jump up to redline at that speed when it starts its upshift downshift shinnanigans... not crazy about it jumpping up to redline, and sometimes its a challenge to get it to shift to get rpm to drop. Crazy at 70 on highway like that!!
Other noteworthy stuff: I had ECU reflashed. no change. I had Juice box programmer unplugged, no change. I had highly recommended tranny shop go thru drivetrain. Good recent tranny maint (fluid change/flush, etc from dealer). No issues, nothing in fluid, servos, various other stuff checked. To use his words, The more things he did or looked at, the more he was convinced the transmission components are NOT the issue...and that it was a response to something else he could not find. Some signal or voltage spike...bad sensor signal intermittent, grounding issue, wire chaffing... something like that is suspected.
Going crazy, truck is parked, out a lot of time and $$$, freezin my butt off commuting on MC, and weather aint doin nothing but gettn colder. Buying a used jeep this week to get me by, so i can take time with this issue. I did surf this site a little and saw some similar stuff... but Now I throw this out to the guruland here as my first post. Any leads or ideas would be GREATLY appreciated as Im not sure what to try next

 

Have you checked the truck for codes? If not, use the key trick and report back.

 

WELCOME to DTR!!

My first question is what exactly happens when the engine speed shifts back and forth? Can you feel it surging even though you have a steady pressure on the pedal?

At idle does the tach stay steady at 750ish or does it jump up or drop down?

 

Yes, steady on pedal, or cruise on with a steady input on flat terrain, the tranny is shifting around, I see the load increase and decrease on my attitude display, and yes, the truck does some surging at it goes into "too low a gear selection at that speed" and then back again.
Anything below 45mph, it performs status quo, including at idle. No issues at all.

I found some data to keep me occupied, looking at various grounding points, looking at wires for various chaffing signs or possible grounding points, but im just scratching the surface of that research, i havent started to do that yet. Thanks for the replys so far.

 

Well, I dont have any engine lights, and the dealer told me i have no codes. The tranny shop guy commuted in my truck with some diagnostic equipment, he experienced the problems but as i said, couldnt find the issue. He too, mentioned there were no codes.
That being said... I will look around here and see if i can figure out and perform "the key trick", as i have no idea what that is (Im a gas turbine guy, dont know much about auto mechanical stuff and diesels in terms of electrical and electronics stuff, as i dont really have time to apply any interest I may have for it outside the basics... yet)
Thanks for the lead.

 

Sounds like the converter is unlocking. I'm willing to bet you drive with a "light" foot. Engine load comes light and the tranny goes into coast mode, TC unlocks. Then the speed falls and you give a little pedal, load goes up and TC locks up again. I had a silverado with the same issue. Nobody had a fix and I never found one. The reason it wont do it over 70 is that the load is too high. Under 40 and the load is too light. The computer wants to unlock the TC so you can coast down hills at 0 throttle. If the TC remaained locked, you woud have some engine braking.
That's my guess. Good luck finding the solution. That's a very tecnical issue that won't be in the books. Try finding VERY reputable tranny shops and describe the lock / unlock problem. Try Bob at Southbend.

 

"CaptainKelly": I hear what your saying... goin out into "im not sure here but" territory... but... I was under impression that the tow/haul button simply locks in the T/C. If that is the case, and i select that feature... It is locking in then, and i still have the problem regardless. Thats my assumption, is my understanding of it correct?

"Shorts": i figured out how to do the "keytrick" (godbless youtube for some useful info sometimes). Now if only i left wifey the key to get in truk and do it and report back. I will repost the result tomorrow on that.

 

It's possible the transmission control module is acting up. Make sure they flash that, and ONLY that. ECM is for the engine only!!

 

[QUOTE=adventureduc;3145676]"CaptainKelly": I hear what your saying... goin out into "im not sure here but" territory... but... I was under impression that the tow/haul button simply locks in the T/C. If that is the case, and i select that feature... It is locking in then, and i still have the problem regardless. Thats my assumption, is my understanding of it correct?

Tow / Haul is an alternate "shift schedule" that makes the TC lock up harder and increases shift points to keep the load closer to peak torque. TC lockup pressure is higher to prevent flaring and slipping clutchplates. Higher pressure within the tranny clutches too. Old school Tow / Haul was an OD lockout. Now with all the benifits of computers, we have torque management, defueling, transmissions that match torque to engine load and speed. Way awesome... when it works. Automatics are like two steps away from Merlin to me. And with electronic control, it's harder to diagnose. Before all you had was band adjustment and kickdown adjustment. Now... magic.

 

I did have a code... p0633 ??

 

Skim key code

The truck is saying it doesn't recognize the chip in the key you are trying to start it with.

Any trouble starting the truck? Pull the key out and lock the door with the key, not the fob. Unlock again with the key and try to restart. If you have no luck there, hopefully you have another key to try.

Do you have a programmer or alarm on the truck?

 

Sounds like your TC (Torque converter) is slipping. When you get to around 45-50mph the TC should lockup and not lockup until you go under 40mph. That should be when you notice the coast mode.

Your issue is either a slipping TC or you have an issue with your Governor transducer or governor solenoid. You may also have an issue with the TV motor.

 

i had dealer program two keys... they work fine..just popping that code i guess. no issues with keys of any sort.

yes i have an edge juicebox with attitude. i have already disconnected and ran truck, same issues, so im pretty sure its not an issue.

so i guess i get a reasonable day weatherwise, i will check various wires and grounding spots, look for damaged wire etc. tranny shop tells me my tranny and tc r fine (second opinions never hurt) but thinks its a signal issue from somewhere else, so, thanks for the tc ideas... not sure what i personally will do with that..after i check wiring stuff. thanks for the direction, check back with findings/ results in a few days.

 

BUMP Bro.

 

2armor...(nice stats on your rig, youve been upgrading since i remember...) i godda 12 gauge, and a fawty... and if i raid your stuff... a fiddy too! nice stats... now get off the left coast, and helps yo bro fix his chit!!! I got more advice than the president has bad ideas, and looking for wiring issues and grounds etc is driving me . At least if you were helping...i could hold the hammer and do this to you cuz this cold driveway research is making me . (ok...enuf with the emoticons...had to vent... this is frustrating!!!) think im gonna try "06ram2500" advice (as this loses me nothing) and reflash the transmission control module. probably cheap and i can rule it out (mostly)