1st post, be patient. Have 1994 Dodge, Cummins diesel, 157,000 miles. Recently had the evaporator? replaced. Dash removed. Same time had trans. oil/filter replaced. Used the proper oil. Since then, especially in cold weather, the transmission will shift and engine gains 500rpms. Doesn't matter what speed, in or out of overdrive. Had truck back to shop, they're clueless. Probably need to take back to dealer or good trans. mech. Thought I'd try here first. Don't have much knowledge about engines so if there's some help please keep it simple for me. Thanks. P.S. when it shifts and gains 500 it doesn't take long for the engine to drop back to normal rpms. Just keep repeating itself.

 

TPS, is my first guess. Do a search. It stands for throttle position sensor. They have a tendency to get dirt and crud in them, as well as the tps wires picking up interference from other wires along side them.

The fix is to remove the tps, try to clean it by disassembling (it's not supposed to be taken apart but can be done), and/or isolating the wires or separating the 3 wires of the tps away from the rest of the wires they accompany in the harness. Not hard to do but time consuming.

The only other thing I'm thinking is maybe the temp (how cold?) is cold enough to affect the trans temp sensor. Some models are not supposed to go into OD if the fluid temp is less than 120 degrees? I'm not totally clear on that so perhaps others can help. Also check the connections on the trans itself to make nothing is loose. Good luck, Kevin

 

Thanks Kevin, where is the TPS located? Trans. shifts up/down even when it's warmer, say 60-70 degrees outside. Even when the trans. has had ample time to warm it can be bothersome. This morning, 25 degs. outside, had to go 5/6 miles to town. Wasn't much of problem. Didn't stay long and on way home the shifting was terrible. Anyway, thanks again. Don't know when, but I'll let you know how I make out. Tim.

 

TET:

If your transmission is "hunting" (going into overdrive and back out of overdrive when you apply a small amount of throttle) between 3rd and overdrive it is probably the TPS. The TPS is located on the drivers side of the P7100 Injection Pump. It is a small black plastic box that is 1-5/8" square held in by two 10mm bolts and has a connector on the bottom. It is nothing more than a rheostat that is operated by the throttle linkage. The Cummins part number is 3930318 and the cost is about $145. You can determine if it is not functioning properly by measuring the voltages with a digital ohm meter. Do a search for other posts on the details. I believe Infidel posted how to do the measurements. Recently, I replaced mine as it had a dead spot when it was moved. Some on here have drilled a hole in the back of the unit and cleaned it with contact cleaner and others have cut the unit apart, cleaned it and then used RTV to glue it back together.

If this is not the problem, it could be that you torque converter is slipping and you are in the market for a better transmission/torque converter. I would start with TPS and work your way from there.

John (DH)

 

Check your trans fluid put the truck in neutral not park and idleing and check to make sure it is full if you check it in park it you will not get a true reading I had a similar problem when I did my first tranny oil change.

 

Heres a few days worth of reading

https://www.dieseltruckresource.com/...der=descending

Kevin

 

Haven't had sense enough to think about fluid level. Thanks
Kevin, I'll get to work. Tim

 

Well, fluid level is ok. Before I get involved in the TPS part, I read something of interest on a previous reply to a post that caught my eye. It said that TPS can cause hunting and the "shift lever not properly adjusted."

Like I said when I first started to notice this was after my dash was taken apart. When it was re-assembled the indicator for whether the transmission is in Park, N, D, etc. is not precise. For example if I'm in drive the indicator reads between drive and 2nd. Is this what shift lever not adjusted properly mean? Tim.

 

Sounds like the TPS, it eventually happens to every one of them (mine included).