So I got this 98 12v 4x4 dually for good deal that needed a ton of stuff. So far I've done ball joints, wheel bearings. trac bar, tie rods, pitman arm, shocks, stabilizer shock, brakes, new tires,alignment.
steering box is tight but it still wanders all over the road.The only thing left to do is bushings, would those cause this?

Today, had trouble getting overdrive...123 shift fine. Once it got to the end of 3rd the tac goes crazy and won't go into overdrive. After pedaling it i could get it to go in. Lock up works fine.

Had this problem last week and took it to trans shop...they said trans is in perfect condition.

Of course it wouldn't do it for them.

 

Check the TPS voltage?

If not that, get a shop that will plug in a scanner and go for a ride with you. Shouldn't be too awful to find the problem. Fixing it might be another story.

 

The scanner did not get any codes. I'm going to check tps tomorrow. does the tac get a signal from tps? Or could the tps make the computer go crazy and mess with the tac and trans?

thanks.

 

Mess with the tran, yes. I don't think the TPS will affect the tachometer at all.

 

I had the same problem. Put trans temp sensor in and it would fix it for about a month. Put a tps in today, did not replace the trans temp sensor and seems to fix it. Guess I'll see in a month.

 

i fought your same problem seemed like forever. went down the same path with troubleshooting. i ended up removing tps and installed a potentiometer and dialed in my own voltage and havent had a problem since. if there is a downfall to this its the tc stays locked in once it goes in. also the tc will not unlock during decel until under 50mph in my case then it unlocks. i tried everything from drilling holes in the tps to clean it to putting foil around wires of the tps to shield them. i even elongated holes in tps to adjust voltage. all this would work for a little while but i was always getting back to having same problem. i could not see the point in spending over a 100 bucks for a new tps just to have the same problem later. the potentiometer route is under 20 bucks. anyone else with an opinion on this, feel free.

 

Take a look here.

Dodge diesel maintenance tips

 

That's a good link...thanks.

I checked the tps and everything was fine. I ended up taking my truck to a guy who specializes in Cummins. I told him the problems I was having with the shifting and the tac going crazy...he laughed and said crank position sensor. Turns out that the crank position sensor was just out of adjustment. No problems so far.

I also had him advance the timing to 16 deg, fixed the kdp, #5 fuel plate, and turbo waste gate block off. After he was done with it I did 4" turbo back exhaust and gauges (exhaust temp, tranny temp, and boost).

Thanks for all the input!

 

good to hear jb, just remember the tp sensor can do the exact same thing to the trans. some people install a diode(filter) some replace the tp. some clean the tp. some install a potentiometer on the dash to make their own adjustable tp, this may give better results for the RH trans guys. im not sure how that affect RE trans. i think tp infuences governor pressure on RE where the RH shifts hydarulically untill o/d or lock-up. i have never messed with this so im not too sure.