Diagnose My Odd Transmission Issue-2008 Ram 2500 Diesel

Discussion in 'Off-Topic' started by Neepuk, Mar 13, 2017.

  1. Neepuk

    Neepuk Going, Going, Gone

    Location:
    Redstone, Colorado. Population 96
    Name:
    Chris
    A question for the automatic transmission experts...
    I have an 08 Ram with the 6.7 Cummins and a 6 speed automatic trans. The truck has 110,000 miles on it and I'm now experiencing an odd transmission issue. I'll try to be as detailed in my explanation of the symptoms as possible.

    While cruising in "D" at 55 to 63 mph the truck is in 6th gear, if I depress the gas pedal to accelerate moderately the transmission seems to shuttle down and up between 5th and 6th gear for about 10 seconds before settling on a gear.

    In the same scenario if I hammer the throttle it downshifts to 4th and accelerates hard as it should, then continues to shift up through the gears as it should...

    If I switch in to manual mode and select the gears with my thumb the transmission goes in to whatever gear I select and holds perfectly in every gear under the same circumstances stated above that normally cause the shuttling between gears.

    I also get the shuttling issue in one spot on my drive home on a daily basis.... there is one section of road on my way home that is a slightly steeper uphill grade than the rest of my drive. The slightly steeper section is about 2/10th of a mile long. I always go about 61 or 62 MPH steadily on my way home. In this mildly steeper section the transmission will do its funky shuttling to hold speed if I'm using the throttle with my foot, but if I'm in cruise control the transmission will downshift to 5th and hold exact speed until I reach the crest of the hill then shift back to 6th.

    It's a weird deal... I can easily keep the transmission from presenting its problem by adjusting my driving style but I know that it's just not right. I do adjust my driving style to prevent this from happening as I know that this back and forth can cause further damage, and I've only allowed it to happen enough to understand exactly under what circumstances the problem arises.
    The truck is going in tomorrow to a reputable transmission shop for diagnosis, a scan, and a service.

    I'd like to hear if any of the SBR wisdom can hypothetically diagnose this and get an idea if this is likely to be a high dollar fix?
    Thanks!
     
  2. cheez

    cheez Master of the Darkside

    Location:
    Livermore, CA
    Name:
    cheez
    My guess (entirely guess based on what I've read about the transmissions in the Dodge Cummins diesels) is torque convertor clutch isn't locking up fast enough. It sounds like the ECU's calling for a downshift to 5th, that the transmission tries to do it, but the TCC doesn't lock up quickly enough and it fails back to the previous gear.

    I went through something similar at ~100k with my '01 1500; replacing the TCC resolved it (similar kind of bouncing or pogoing between gears) and that was the diagnosis and fix.

    Hopefully someone with actual knowledge will offer better input.
     
    3stripes and Neepuk like this.
  3. RobertHaas

    RobertHaas Gone to Facebook

    Location:
    Salinas
    Name:
    Robert
    Not a a transmission issue. A TPS service/reflash should help.

    TPS=throttle position sensor
     
    3stripes, Tim, cheez and 1 other person like this.
  4. Neepuk

    Neepuk Going, Going, Gone

    Location:
    Redstone, Colorado. Population 96
    Name:
    Chris
    My mind is leaning this way too since there's a difference between how it acts in cruise control vs accelerator pedal. Sure feels like the trans is acting up but I also fully understand how a TPS reading can throw the symptoms to the trans.

    Due for a trans service anyway so I'm looking forward to hearing what he finds in the pan, filter, and on the scan tomorrow.
     
    cheez and LoopDuplicate like this.
  5. RobertHaas

    RobertHaas Gone to Facebook

    Location:
    Salinas
    Name:
    Robert
    The transmission has its own computer

    The Cummins has its own computer

    The truck has it own computer

    They all communicate through the CANBUS

    Find a smart guy like @Tim near you. They will have the ability to plug in and read all three systems in real time. @Tim is grumpy but has the computers and knowledge needed for this type of issue
     
    3stripes, Rex, Tim and 2 others like this.
  6. Neepuk

    Neepuk Going, Going, Gone

    Location:
    Redstone, Colorado. Population 96
    Name:
    Chris
    Sounds like a real possibility as well, also sounds expensive. It seems like it could be that the cruise control is just enough smoother than I am at adjusting the throttle input to be the difference if it's just beginning to fail.
     
  7. LoopDuplicate

    LoopDuplicate Well-Known Member

    Location:
    Hollister Hills
    Name:
    Jeff
    @Tim has a private profile :)
     
  8. cheez

    cheez Master of the Darkside

    Location:
    Livermore, CA
    Name:
    cheez
    Was about $1k on my 1500, probably another $3-500 for the bigger truck, but it sounds like people with actual knowledge have come along. ;)
     
  9. Neepuk

    Neepuk Going, Going, Gone

    Location:
    Redstone, Colorado. Population 96
    Name:
    Chris
    I hear that! Mechanics are a dime a dozen but technicians are as rare as hen's teeth.
    The transmission guy it's going to is an honest and trusted expert around here. I can trust that he will do a great job assessing the current state of the transmission and servicing it. I'll have to start there knowing that it's ready for a service anyway.
     
    cheez likes this.
  10. Andrew

    Andrew This Land is Your Land

    Location:
    San Jose
    Name:
    Andrew
    If it's a transmission problem.
     
  11. ghostbuster

    ghostbuster Well-Known Member

    Name:
    Pete
    Because it only acts up on 5-6 shift doubt it is a tps problem. Check for computer reflashes for this concern. If the transmission computer uses a clutch volume index parameter I would clear them all and perform a relearn before going any further with diagnosis.

    Also try lightly applying the brake to get the trans to shift out of lockup without shifting to a lower gear then let off brake to get TCC lock up to occur while holding the accelerator at a steady state. May need a scanner to ensure everything is happening properly to get accurate results. If you feel the shudder when the TCC reengages then the TCC on the torque converter is failing, assuming the signal to the lock up solenoid is good.
     
    3stripes, Tim, cheez and 1 other person like this.
  12. Neepuk

    Neepuk Going, Going, Gone

    Location:
    Redstone, Colorado. Population 96
    Name:
    Chris
    Even IF my problem is not a transmission issue the text you quoted is true.

    I didn't not say that the issue will be gone and the truck will be repaired if it's not a trans issue. The current state of the trans will be accurately assessed and it will be serviced. The issue will either be identified and approved by me to get repaired OR the transmission will be ruled out as being problematic.
     
  13. Neepuk

    Neepuk Going, Going, Gone

    Location:
    Redstone, Colorado. Population 96
    Name:
    Chris
    Thanks! I totally forgot about the light use of the brake to check torque converter lock up.

    Does TC lock up only happen in 6th gear in this transmission? Or does that happen in any lower gears too?
     
  14. buellistic

    buellistic Well-Known Member

    Location:
    Riding the Sierras
    Name:
    Dan
    Whenever I have a problem with my car.truck.bike.
    I go to a mechanical forum about my said problem.
    And read about everybody else's problems and misery to find the fix..
    Then go online and buy the part.
    Problem solved!
     
    3stripes likes this.
  15. RobertHaas

    RobertHaas Gone to Facebook

    Location:
    Salinas
    Name:
    Robert

    Brake application with the throttle open will result in the CPU shutting down the injection circuit.

    The reason I suggested the TPS is you rarely if ever will roll along with steady throttle right in the shift point. Also the fact that it is eliminated with the cruise control being engaged. The sensitivity and sample rate from the TPS to the ecu is what it sounds like to me.
     
  16. ghostbuster

    ghostbuster Well-Known Member

    Name:
    Pete
    Code set criteria for TCC trouble codes states that lock up can occur in gears 2-6 IF conditions are correct BUT a condition has to be present for longer than 10 seconds to set a trouble code.

    The fact that it happens only in the 5-6 range and no check engine light it not enough IMO to rule out a TCC/transmission problem. Testing is required.......and it is a Chrysler transmission :)
     
    Tim likes this.
  17. ghostbuster

    ghostbuster Well-Known Member

    Name:
    Pete
    I'm no Cummins expert but I presume the decel fuel cut functions like all other manufacturers. Closed throttle indicated, brake switch input, above a certain Rpm and mph are inputs needed to go into fuel cut mode. Quick verification is cruise at problem speed, apply light brake pedal and lightly roll on throttle. If rpm picks up a few hundred rpm or more (rpm rise has to be above the rpm drop when TCC lock up occurs) then you are not in fuel cut. If you keep the throttle applied when you step on the brakes during TCC testing there should be no decel fuel cut.
     
    Tim, Neepuk and RobertHaas like this.
  18. ghostbuster

    ghostbuster Well-Known Member

    Name:
    Pete
    You can easily rule out tps by monitoring the signal when the condition occurs with a labscope or high sampling rate graphing multimeter or possibly a quality scanner with high sampling rate graphing capability monitoring just the TPS PID. No dropouts means no problems with TPS.

    I should add easy for well equipped mechanic, not so easy for a neepuck.
     
    Tim likes this.
  19. Neepuk

    Neepuk Going, Going, Gone

    Location:
    Redstone, Colorado. Population 96
    Name:
    Chris
    I'm going to go try this in the exact location where I generally have the issue. It's going in to the shop tomorrow regardless, but my curiosity has the best of me now.
     
  20. Motech

    Motech Mr. Logorrhoea

    Location:
    Santa Cruz
    Name:
    Steve
    This is nothing new under the sun. Likely not TCC related, just hunting for correct gear in the grey zones like all 4 and 5 speed EAT truck apps before it.

    With Cummins, as Haas pointed, the proprietary engine control module used remote from PCM complicates the load calculations, especially with a diesel, and this is why TPS inputs are more critical.

    Reflash may cure it. Switching to "tow" or "OD OFF" mode should eliminate most of it too.
     
    cheez and RobertHaas like this.
Loading...

New Posts