In OD RPM up/down

[Joe Mc]

RPMs slightly increases by 100/200 for a second or so, then back to whatever it was. 5-10 seconds later same thing. Seems more prevalent on level to incline. Only happens/notice when in OD.

Last fall same thing and was told trans output speed sensor was most likely dirty, remove and clean. Did that and resolved issue. I also changed trans fluid & filter. A few weeks ago this RPM up/down started again? I plan to clean sensor today or tomorrow and will post before and after pictures along with results.

Biggest question I have is, why so soon is this happening. This has "never ever" happened before. I've owned this truck since 05/01, got it with 75k, at 130k roughly 06/04 trans started slipping on 1-2 shift (whole truck was stock). Had a DTT built, then dropped a few bombs = see signature, that trans lasted till 260k roughly 10/20. Had same shop that built the DTT (TRE Performance, VA Beach, VA) do build = tripleloc converter, flex-plate and similar performance build to handle more than HP & TQ engine makes.

Lastly I've maybe put 8k miles on it since rebuild. Warranty was for 2 years. I don't drive it much anymore maybe every, or every other weekend. Since I last cleaned the sensor I might have put 1k miles on it.

Any idea what is causing this?

Thanks

 

[petersonj]

It sounds like the torque converter is unlocking / locking repeatedly and randomly. Not likely a transmission problem, but rather some kind of electrical interference that is sending false signals to the convertor lockup control circuit.

Your mentioned symptoms have been reported for years on the second generation VP44 trucks. People have added suppressors, capacitors, and other products from vendors to alleviate this problem only to find that the symptom returns.

I would be checking the whole electrical system in regards to clean, tight battery connections (positive and negative) and the many frame and body grounds. Poor connections at these locations can lead to excessive AC voltage present in the charging system.

Have you heard of the W-T ground reference wiring modification and if you have, have you done the mod? This mod has reportedly cleaned up the converter lockup hunting issues for many people.

- John

 

[Joe Mc]

It sounds like the torque converter is unlocking / locking repeatedly and randomly. Not likely a transmission problem, but rather some kind of electrical interference that is sending false signals to the convertor lockup control circuit.

Your mentioned symptoms have been reported for years on the second generation VP44 trucks. People have added suppressors, capacitors, and other products from vendors to alleviate this problem only to find that the symptom returns.

I would be checking the whole electrical system in regards to clean, tight battery connections (positive and negative) and the many frame and body grounds. Poor connections at these locations can lead to excessive AC voltage present in the charging system.

Have you heard of the W-T ground reference wiring modification and if you have, have you done the mod? This mod has reportedly cleaned up the converter lockup hunting issues for many people.

- John

Thanks John
Probably 20 years ago I resolved the hunting situation which only happened around 40-45 depending on grade. Used the DTT filter and later did the wiring mod, just because.

When (described in initial post) first happened my initial thoughts were TQ hunting. I read instructions for DTT filter and checked with volt/ohm meter and it was dead on.

The situation I had last fall and more recently happens at any speed above 40 and still occurred if OD was turned off or not. I could be going 50 or 70.
Thanks for your reply.

 

[Joe Mc]

Update
The sensor wasn't really very dirty. It did have a very little bit of material see picture. I was surprised that such a small amount would cause the situation. I cleaned, reinstalled and went for a test run.

Once on the highway the RPM fluctuations started again. I had to drive about 25 miles to the next exit so I stopped in town 3 times for a few things shutting truck down.

Was fully expecting the same deal as I entered the highway for home...miraculously the RPMs were rock solid all the way back 55, 65, 70. Pretty odd for sure but I'll take it.

Going to order a new sensor today.

 

[petersonj]

You may have resolved the issue or you may have not.

If it is in fact caused by electrical interference, the symptoms will likely come back.

The situation I had last fall and more recently happens at any speed above 40 and still occurred if OD was turned off or not

The symptoms can occur whether or not "Overdrive" is locked out. The symptoms usually go unnoticed in 3rd gear because the transmission spends more time in 4th gear than 3rd gear. The symptoms may also feel different because the gear ratios are different.

Finding the cause of a possible electrical interference is like finding the cause of death wobble. People say "I found the worn part that caused my death wobble", and then 3 months later it happens again.

- John

 

[BigPapa]

The symptoms can occur whether or not "Overdrive" is locked out.

This is correct. The issue is the TCC locking and unlocking, nothing to do with OD. Is it happening with cruise control on and off?

 

[Ozymandias]

Does the rpm swing in real or just the tach showing a swing?

 

[Joe Mc]

This is correct. The issue is the TCC locking and unlocking, nothing to do with OD. Is it happening with cruise control on and off?

Happened with cruise on "and" although I had to brake (disengaging cruise, but not physically turning cruise off = cruise light still on) to slow down for single lane for a few miles, as I steadied speed fluctuation continued. Understand this fluctuation, a bit hard to explain, is like driving along and the tach (and audibly the engine RPMs) will increase maybe 100-200 for a few seconds then go back for a period maybe 5-10 seconds, sometimes it would remain normal for longer 20-30 seconds before the increase.

What happened after cleaning sensor yesterday = continued to fluctuate for 1st drive 25 or so miles then stopping in town a few times (shutting down each time) - then after getting on highway back to home no more fluctuation - seemed very odd for sure. Previous time, last summer/fall, this fluctuation 1st occurred and I cleaned the sensor, the fluctuation was gone immediately.
I might take for a ride later today or tomorrow to see if it happens. Will report back.

Do you think adding a new ground strap, say from bolt an unused bolt hole on block or head to screw holding PCM to body would be an idea? I'm thinking that couldn't hurt?
Thanks

 

[Joe Mc]

Does the rpm swing in real or just the tach showing a swing?

It is real = can hear and feel engine fluctuations.
Thanks

 

[Joe Mc]

Took truck out today for a 70 mile +/- round trip, 55 or so were highway at 65 mph. There were no RPM fluctuations cruise on or off. At the ½ point I fueled up. Get in start truck and fuel gauge is below E, just like when everything is off, all other gauges are fine. It was at 1 notch above E when I pulled in for fuel. I turned the truck off and on a few times and no change. I'm like "now what"! Headed home, drove fine, gauge still on E. Pull in to driveway, let it cool down before shutting off, gauge still on E. Went through armrest storage cleaning out some old papers and stuff, bout 5 minutes or so. Decided to turn key on (no acc) and gauge went to F?

Never thought I'd even think this but, I've about had it with the electrical anomalies in this old truck. I totally suck at electrical trouble shooting. Over the years I've looked at the wiring diagrams in the Dodge FSM I have and for the life of me they make no sense, just can't understand them. I can take almost anything mechanical apart and rebuild/repair it, but when it comes to auto electric diagrams I see Greek.

Any ideas. I'm sure everyone will say check all grounds and I would if I could figure out where "all of them" are. Frustrated and wish there was an auto electric place around where I live.

Thanks

 

[petersonj]

Since you have unwittingly admitted that you have looked at the FSM, there is a section that shows where all grounds are located. Just sayin...,

It could be that the ancient fuel sending unit in the fuel tank is expiring.

- John

 

[Joe Mc]

Since you have unwittingly admitted that you have looked at the FSM, there is a section that shows where all grounds are located. Just sayin...,

It could be that the ancient fuel sending unit in the fuel tank is expiring.

- John

I did look at wiring diagrams in FSM but also said it looks like Greek to me. Perhaps I missed something? Can you guide me to where it shows all grounds? As for fuel sending unit I did replace it sometime ago, forget when? At least it isn't the original.

 

[Topzide]

@Joe Mc, The grounds should be listed like - G156 - G = ground and 156 is connection point. W = wire color of white, W/BL = white wire with blue trace and also the number is connection point. Hope this helps with some of the "Greek" that you're running into! I pick up a Power Probe III and it really helps with wiring issues. Good luck.

 

[Joe Mc]

@Joe Mc, The grounds should be listed like - G156 - G = ground and 156 is connection point. W = wire color of white, W/BL = white wire with blue trace and also the number is connection point. Hope this helps with some of the "Greek" that you're running into! I pick up a Power Probe III and it really helps with wiring issues. Good luck.

Thanks. I'll take a look in the FSM. So, the "connection point" tells you where on the body/frame the ground is attached? I do have a test light and also a Fluke volt/ohm/amp meter. Just a whole lot confused with auto electric

 

[Topzide]

In theory, yes. not sure how the numbering translate to location on the truck. Might be a grid system if a paper diagram. The USB manual gives me a 3D type of view where the connection is located. Sounds like you have the equipment needed for your truck. Good hunting!

 

[BigPapa]

This is described as “2001 and Earlier Ground Locations”

 

[Joe Mc]

This is described as “2001 and Earlier Ground Locations”

Awesome! Thanks. Hope this helps me (extremely limited auto electric abilities) figure things out. Printed and will keep in FSM. As I'm working outside all I need now is a day that its not raining, too cold and I can take a brake from working on the house. Probably not anytime this week.

Thanks all that replied.