Sorry for a horrible title, but it’s the best I can describe it in the limited characters I am provided for a title.

I am going on the assumption that this is entirely torque converter related since it does it based entirely on speed and happens at typical lock-up speeds (I think)

With O/D off, light cruising throttle (which I assume locks it in 3rd gear) the problem is between 30 and 40 (roughly)

With O/D on, same light cruising throttle the problem is around 43-51mph

Basically I can feel the truck shift 3 times (into 4th) then it will surge forward when I assume the torque converter locks and if this happens in the above speed range and I am trying to accelerate even the smallest bit, it unlocks and my RPMs jump up, then it locks again and so on till I either floor it or drop below speed. Until I give it enough throttle to cause a downshift, the variations in RPMs get larger and larger.

Say I’m rolling at a speed where the engine would be around 1200 locked. If I have my foot into it, the RPMs will bounce between 1200 and 1800, and I do mean bounce, as soon as it gets to one end the tach shoots back to the other and the truck bucks violently. I don’t have the slightest doubt in my mind that this is horrible for every inch of my driveline.

I normally just drive around the speed ranges but lately its gotten really bad, ****** me off to no end because I’ve spent HOURS behind people doing 45-48mph and had to keep clicking the o/d button to keep from bucking while ruining my fuel mileage which already sucks.

It will try to pull itself up a solid hill at 1200rpms and wont downshift till its dropped down to **** near idle, its like it has no idea what gear it actually needs to be in.

The weird part is, about 2 months ago it was fine for at least a solid month. I remember looking over to my buddy and saying “hey did you feel that? That was a proper downshift right when it was supposed to be”

I have no idea what it could be but I think I might replace the APPS

This is one of a several post series but I think they might all be related.

I *think* an APPS problem can cause fuel mileage issues, and if the engine isn’t getting a APPS signal it could cause a dead pedal sort of event like I said in my fueling post and I assume it could easily cause a transmission issue like this.

Any ideas?

 

First, check to see if you have any codes stored. Then, check the throttle valve cable to make sure it's properly adjusted. If it is and the problem still exists, put a pressure gauge on the governor test port on the trans and observe the pressure reading before and during this "bucking". (Obviously, you will need a hose between the trans and the gauge long enough to allow you to route the gauge into the cab while you're driving down the road.) Could possibly be the gov. solenoid and/or gov. transducer.... the pressure test will help determine this.

 

Roger that, thanks

The transmission is heavily built as of a year+ ago

I'll probably go bother him again and see if he wants to mess with it.

 

Could this be the TC locking and unlocking problem? If so, start by cleaning the battery terminals, then the ground connections under the battery box. If this improves the condition it is electrical noise. Many posts on this. Get a noise filter from DTT. Could also be caused by bad batteries.

 

I started watching it even closer this last time out

My engine will be around 1500rpms in 4th, then the T/C will lock and the engine will drop to or below 1300rpms which will cause the T/C to unlock which causes my RPMs to rise again...

It just seems that 1300 is the magic number. Its really getting old because it will stay locked on a hill untill it slows down under 1300 or I give it enough throttle (more than 75%?!) to make it downshift

The roads I have been on lately seem to run about 49mph which means I'm O/D off cruising at 2200rpms which seems to be killing my mileage

i dont know, I hope I can get this sorted out in a big hurry

Its also dawned on me that my ECM, PCM whatever might be bad

There is no reason I should get 9MPG under "normal" city driving conditions. heck I dont think I was getting 10mpg the last time i was on the highway