I've asked this question long ago and it never really went anywhere. My hope is with all of these new members that someone might hold the key...

Background:
I've owned my truck for a year and a half now. I got it in April (April is a cool month in Ohio - keep that in mind). It is a 1995 Ram 3500 4x4 Diesel Automatic. I am the third owner. I got the truck with 91,000 miles on it. It now has 114,800 miles on it.

Problem:
It started in early summer. Probably around June. When I am driving down the road, at highway speeds, my tach jumps about 200-300 rpms. It's not just a visual jump... I can feel the engine jumping those 300 rpms. Heck, anyone riding in the truck would be able to feel it. It can happen just once on a trip, or it will jump every second for an hour or more on the road. It's very annoying and very concerning.

Last winter, it stopped doing it all together. Not once during the cold months did the tach even attempt to jump. Now why would a problem not show up during the cold months? Anyway, I got through the spring without much trouble as well. But in July/August it came back. And it has been doing it ever since then.


Now, I will be the first to admit that I don't know a lot about my truck. I know some, but this one baffles me.

I think it has something to do with the last gear or overdrive or something. Because the tach does not jump at less than highway speeds. It's hard to explain, but with my truck it accelerates slowly until it hits about 45mph and then something "locks into place" and we gain speed quickly. It's during that last "lock up" that the problems arise. It seems to go in and out of that. Is this just the last gear? Is my last gear slipping? Is it my TPS? Or what?

The same thing happens when I turn Overdrive off (although it didn't used to. This is a relatively new thing). When it does it's last shift or "lock up" the tach will jump.

I've taken it to a dealer and they could not reproduce the problem, so they couldn't do anything for me. And there is no way for me to force it to do it. It's completely random. I try being very light footed and I try flooring it and sometimes it will do it, sometimes it won't.

Any help?

Thanks in advance.

 

My TPS was causing mine to act that way. After I rebuilt the trans it was amplified 10 times over, I assume it was because of the incresed line pressure. I bought a new one but, i've read that they can be cleaned.

 

Yep, sounds like the TPS. You can take it off and spray some cleaner in there to clean the contacts.