Hello all... Long time reader, first post... and man do I need some help!

I have a 1995 Dodge 2500 4x4 12V Cummins w/ Auto 47RH....

The tranny had been having OD issues of going in/out of OD when close to "that" speed (55-65) it would go in/out of "lock-up" if you tried holding at say 60 mph foot driving and you could not use CC at all; however, it would always stay in 4th (OD) when using the TC lock-up switch.... Then last week after doing some pump tuning (torque plate/afc adjustment) I took it on a test drive and no OD, even with the lock-up switch flipped...

So I tested the TPS signal @ 0.4V... tried adjusting it w/ no luck... tried cleaning it and then I got 4.96V from the orange/white signal wire at idle... figured the TPS was gone... so I order a new TPS this w/e and got it today... installed it and still getting 4.96V from the org/wht signal wire at the TPS... I checked wiring on the TPS all the way to the computer and it was OK... ran new wires just in case and still 4.96V... Checked the Temp Sensor and it seems ok.... checked wiring on TC lock-up switch and it is ok... just replaced the throttle linkage (adjusted it right).... The only thing I'm not sure of is the "OD Off" switch on the dash... it is "well worn" (can't really feel anything when it is pushed, but I never used that much so I can't remember if it clicked when pushed or not)... anybody have any ideas or seen this before??

The 4.96V at idle has me stumped... its at that voltage even without the truck running... I figured that it was just a wiring issue, but that all checked out..??

The tranny & TC lock-up switch work perfectly in gears 1-3 but it will not shift into OD... No fluid leaks, tranny was rebuilt with the all the good stuff about 20k miles ago...

 

what about a noise filter on the tps line?

 

I can try that tomorrow maybe... I have a couple of capacitors that are about the right size... I just didn't think that there could be enough noise to produce that kind of voltage... worth a try though since I already have all the wires located at the PCM... should the capacitor be ran between the ground and signal wires at the PCM?

 

not a capacitor, You need an actual noise filter with the correct setup for this application! Its not really about the voltage, it's more so if you put an oscilliscope on the line, you'll see that the noise (voltage or not) created by the charging system and so on can cause irratic shift and TC problems.

DTT sells a noise filter as do many other vendors! There's probably a post regarding building your own but I've never done any research in that area!

 

if ur OD off switch is bad or unhooked u'll have no overdrive took me a while to figure it out, i was panickin

 

do ou think the od switch bing bad on a 47re would do this as well? sorry not trying to jack the thread but have a similar issue

 

I will look into the filter today, probably put it on a scope before I buy something.... I will also check out the "OD Off" switch this evening....

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Well I got home from work and wanted to check out a few things before trying the filter...

So I took the new TPS off and checked to see if resistance was changing when the sensor was being turned, it changed perfectly (~2.5kOhms at idle position/~.6kOhms at WOT position); however, still a constant 4.96V when key on, engine off/idle position with no change in voltage as sensor was turned...

While at work today I made one of the POT OD controllers... so I figured I'd give it a try even though it looks like there is no issue with the sensor... I hooked it up and could not get the voltage to dial in like it should...it would go from .2 to 4.0+ Volts very quickly... when the engine was running anytime I dialed the POT in over 0.25V my Tach would quit working and the Check Engine light would come on... So I decided to take it out on a test drive set at 0.25V... drove it and it shifted into OD but not like I would want it to.... also while in OD, I checked to make sure the "OD Off" switch was working correctly and it was....

If there wasn't issues using the POT (voltage not right, tach not working properly) I would mount it on the dash and be done, but even with the POT there is something not right.... I'm going to check out the wiring for the tach, CPS, etc here in a bit...

I'll be working on this until its fixed... so any help is appreciated...

 

I'm glad you got some progress! I know how annoying these problems can be! I'll get any wiring diagrams or any information I can! Just let me know what you need!

 

A wiring diagram for the TPS, CPS, and Trans Temp Sensor would be awesome... Is there anything else that is looked at by the PCM for OD?? Check back in later... Back to the garage... Thanks a lot...

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Well I've elimnated basically everything other than the PCM itself... I get 4.96V on the Org/Wht signal wire even with no sensor plugged in.... I'm pretty sure that the Org/Wht signal wire runs directly from the TPS to the PCM... right?? So if it is showing 4.96V without being plugged into the TPS then the only possible explanation is a short inside the PCM right??

Has anyone heard of anything like this?

 

Ground ground ground ground
check the pcm ground, clean the ring terminal and the painted surface where it sits!