Quirky Tranny Shiftdown

[Nemo]

Guys,
I have read all of the forums concerning the TPS sensor, Throttle cable adjustments and I have turned my FSM into a big bunch of black pages, et cetera. All were very informative but has not relieved my issue.

I have done the acceleration tests provided in the FSM, from you guys online and I don't have a problem with erratic shifting, or not holding gears when they are manually selected.

How I do reproduce this issue is no matter what speed I am going the moment I touch (reiterate just touch - not enough to truely brake) the brake pedal the transmission will no longer "Kickdown" to a lower speed to accelerate. The only thing that seems to resolve my acceleration after that is if I come completly to a halt, and then hit the accelerator again or move the gear selector to 2nd and back to D.

I have checked all fuses and fusible links in great length. To verify this craziness, I have also allowed the truck to come to a slower speed, ie 10mph from 30mph, 50mph to 20mph, 20mph to below 5mph and as long as I don't hit the brakes, I am fine with the kickdown.

I just got through testing in 4 low, ie CDL engaged and ABS off and the problem doesn't happen? ABS speed sensor?

Thanks for your input.

 

[cam75w/ls1]

Sounds like the valves in your valve body may be sticking. Was the service intervals on the trans abused any? Does it work really good cold and then seems like the problem appears when it warms up?

 

[Nemo]

thanks for your reply, but if you read my last section on my first post the tranny shifts perfectly until I touch the brake pedal. Doesn't even need to be actual braking, but just touching the brake pedal, ie enough to make the rear lights come on. I have never had a bad service history with this truck. It is def. taken care of. I have been told I may be a little anal with it. The mileage is 183k so stuff will break, so I am not in denial, but confused to a valve being a problem if everything works until I touch the brake pedal.

 

[cam75w/ls1]

I do know the torque converter is wired to the brake light switch on the Gm's and Fords. I'll look tomorrow at work and see how the trans is wired on yours and see if I can see anything...

 

[Nemo]

Not sure about the converter. In the FSM it does state that the brake stop switch? is somehow connected to telling the engine to cut the fuel supply at some level. I will write the details in the AM exactly to what it is referring to. Thanks again.

 

[Nemo]

OK. So here is the Stop Light Switch Malfuction circuit description.

This signal is used to detect when the brakes have been applied. The STP signal voltage is the same as the voltage supplied to the stop lights. The STP signal is used mainly to control the fuel cut-off engine speed. (The fuel cut-off engine speed is reduced slightly when the vehicle is braking.)

Do you guys think this would be enough to keep the engine from kicking back in if faulty.

I guess I need to go pull the switch and see how it performs then?

 

[Bear80]

Do you know if your valve body was upgraded to accommodate the S/C?

 

[Nemo]

If you are referring to the Valve/s within the tranny then no it wasn't and I am not aware of needing to?

 

[Nemo]

Well I finally got out to troubleshoot the Stop Light Switch. Connects into the Brake pedal under the dash. Pulled the wiring harness to it and test drove. Problem goes away. I will be looking for a new switch and installing it to see if I have a wiring problem or if it is the switch itself. I guess I good do the ohm meter, but I am lazy.

 

[cam75w/ls1]

I didn't get the chance to look at the wiring diagrams today at work. I was busy fixing all the other techs mistakes. Just wanted to let you know I hadn't forgot you. Try again tomorrow......

 

[Nemo]

Just wanted to update everyone. My transmission problem is fixed as well as my TPS is solved. It was a bad wire from the ECU to the TPS. It was the IDL wire (Green / White) and must have been toasted somewhere between. The only other thing I have to work on is getting my Cruise Control ECU hooked back in which is a Splice from the Green / White to the IDL of the TPS. Not even sure how much I care being here in the beautiful rockies. CC doesn't do much anyways ... Well I probably should see Christo and Team to get them to clean up my wiring. Have you seen one of them solder. Work of art. Mine... Blobs of metal, but functioning at least.