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Discussion Starter #1
My truck is a '08 Mega Cab 4x4 with 6.7 & 6 speed auto, 35,000 miles.

On the freeway at speed, when you are feathering the throttle, just to maintain speed, it feels like the transmission is jumping in & out of gear. If you lift your foot or depress the throttle, the symptom goes away. This happens when you first start out or with the trans at operating tempature.

I plan to take the truck to the dealer tomorrow. Any ideas what might be the problem? Thanks in advance for your expertise....-Rich
 

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I'll take a stab in the dark and guess it's missing for some reason. Maybe some bad fuel, bad TPS, who knows. Hopefully you get some answers tomorrow.
 

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u joints goin out?
 

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Discussion Starter #6
TC not locked up?
If the TC unlocks at speed will it cause the truck to jolt & clunk? Maybe this is where the service tech should start to look.

u joints goin out?
I crawled under the truck & all seem tight with the drive lines

I'll take a stab in the dark and guess it's missing for some reason. Maybe some bad fuel, bad TPS, who knows. Hopefully you get some answers tomorrow.
No, the engine is smooth & this started about a month ago.

BTW My appointment is next Monday, my mistake....-Rich
 

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Best thing is to have the dealer check it out with a scan tool. They can record the various trans data channels while driving, and then view the recording (or upload it to the STAR Center [Chrysler tech support] for review).

They'll want to see whether the torque converter clutch (TCC) is locking and unlocking, and whether it's actually changing back and forth between two gears. If it's slipping (or not in the proper gear when commanded) then it should set one or more fault codes. If the controller is commanding it to lock and unlock (or shift back and forth) then the question is why? Are the inputs (throttle angle, output speed, trans temp, etc.) reasonable or is one of them going flaky? The scan tool readings will let them see all this.
 

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Are you running a tuner? If so try a less aggressive turbo tune. Found aggressive turbo tuning causing the same issue on mine. Not sure what its doing but you could see it on my monitor.

If not disregard this.
 

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Discussion Starter #9
Are you running a tuner? If so try a less aggressive turbo tune. Found aggressive turbo tuning causing the same issue on mine. Not sure what its doing but you could see it on my monitor.

If not disregard this.
No tuner. The truck is BONE STOCK. In the 3 1/2 yrs I had it I've towed a 35 foot fifth wheel trailer a total of 130 miles.
 

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Thats wild its the exact description of what mine was doing. The vgt mech was jumping. Almost making the eb come on but not quite. Felt it in the transmission like it was coming in and out of gear. I don't see that happening on a stock truck though. Could be in the turbo/egr system somewhere lord knows there is enough crud that builds up in there. Or the transmission could just be a toasted cookie. You're gonna need to get that one monitored problem like that could be coming from anywhere.

Just as a fun question have you ever changed the fuel filter.
 

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i could do the same with my '08, it's a slush box designed for heavy towing and streetability. i think more for the heavy towing. are you running the EB? that may help to slow so you don't have to feather the throttle so much. I've changed my driving habits to allow for more space.
 

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VGT turbo needs cleaned, is my guess. How many miles? Oh I see about 35K doing the math, but it could be since it's bone stock. Regular intervals are about 60K for cleaning in the manual, but you could be sooted up since you don't use it very hard, or often.
 

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Discussion Starter #14
UPDATE:
The truck has been at the dealer for over a week now. The service writer told me the transmission is losing line pressure & the torque converter is unlocking/locking at freeway speed. The mechanic cannot tell which condition is causing which symptom. The dealer called a Chrysler service manager. Chrysler told him all automatic transmissions do that. My service writer said, "NO they don't & NOT like this one is doing." So here I sit waiting for a Chrysler rep to show up & take the truck out for a spin...-Rich
 

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UPDATE:
The truck has been at the dealer for over a week now. The service writer told me the transmission is losing line pressure & the torque converter is unlocking/locking at freeway speed. The mechanic cannot tell which condition is causing which symptom. The dealer called a Chrysler service manager. Chrysler told him all automatic transmissions do that. My service writer said, "NO they don't & NOT like this one is doing." So here I sit waiting for a Chrysler rep to show up & take the truck out for a spin...-Rich
Your tech needs to confirm whether the trans is being commanded (by the TCM) to behave like it is (or not).

What does he mean it's "losing line pressure"? He needs to monitor it (with a scan tool) and compare the actual line pressure reading (from the LP sensor) to the Desired Line Pressure value (from the TCM). If the Actual LP (ALP)matches the Desired LP (DLP), then the line pressure is OK, no matter WHAT the absolute numbers are. Line pressure will vary, based on torque level and other factors. So you can't say, for example, that 50 psi line pressure is "low", unless it's lower than the Desired LP at that moment. And if the ALP is lower than DLP, the next question is: Is the LP sensor reading correctly? He can use a special tool to tap in a hard gauge (along with the LP sensor) and verify whether the sensor reading matches the hard gauge.

He can also monitor the torque converter clutch (TCC) state to see if the TCM is commanding it to lock and unlock.
 

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Discussion Starter #16
UPDATE:
The dealer called this morning. After reading the computer readouts, Chrysler said to,
1-Clean the turbo & EGR systems. (This was done last March). 2-Replace the throttle position sensor.

I don't understand how the turbo & egr is linked to the transmission & torque converter. I do understand the throttle position sensor & transmission link.
 

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UPDATE:
The dealer called this morning. After reading the computer readouts, Chrysler said to,
1-Clean the turbo & EGR systems. (This was done last March). 2-Replace the throttle position sensor.

I don't understand how the turbo & egr is linked to the transmission & torque converter. I do understand the throttle position sensor & transmission link.
This sounds (from my viewpoint) like shoot-from-the-hip, seat-of-the-pants "troubleshooting." Obviously, I don't know what they've checked so far, but for example, you can check the TPS readings on a scan tool, and see if it's responding correctly. Have they done that? Or are they just "guessing" it might be a bad TPS? To me, it's more sensible to check it before you replace it. But again, I don't know what they've done so I can't really pass judgement on them.....
 
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