How do you fix this ram????????

[radar doctor]

2005 4x4, auto ,,ho engine,,,long bed,,,130,ooo miles ,,,,trouble,,,,when you set the cruse control ,,,say 70 mph,,,it will drive ok for a while,,,then the rpm's decrease about 300 rpm then go back to the orignal setting,,,giving you a hestation sensation. . This continues up and down. . period, we have had the ecm replaced at a dealers, no help, finally dealer said some of these truck just have this trait. . We think there is a logical explanation and this can be fixed. . Have any of you had thei problem ,,if so what can we do to fix this... Thanks radar doctor... .

 

[MoparDave]

Just a wild guess but is the Tq converter locking and unlocking?

 

[cerberusiam]

That is definitely NOT a trait, its a problem.



The 300 rpm is pretty close to what the TC gives you on lockup, can you tell if it is locking when it goes into OD? You could try a lockup switch to isolate it unless it is a solenoid problem. Would tell you if the solenoid is not working correctly and all the time.



Its possible its a fuel system problem also, LP, FCA, or even CP3. Have they checked lift pump output? Injector flows? Rail pressure when this happens?



Sounds like your dealer is lost and looking for an exit strategy.

 

[Wingate]

Have a boost gauge?... how does it respond when the rpm changes?. . Like MD said, it could be a torque convertor issue. .

What happens if you turn the cruise off and drive it at a steady speed/load? Does it do the same thing or is this a condition that only exists when the cruise is engaged???. If it only happens when the cruise is engaged, I would take a close look at how the cruise is interacting with the throttle. YOu could be getting something like excessive feedback(noise) in the cruise control...

 

[TCDiesel]

The PCM on controls the Cruise on 03 Autos, the switches are part of the mux communications, the vacuum pump controls the servo on the throttle cable,On top of this, the Cruise is speed related Only. So the system gets So Called (confused) About 50 things may cause this problem.