Torque converter not engaging?

[Gcelevator]

Hey fellas, with all the 4L80E transmission problems around and a friend doing some transmission swapping it came to my mind that my torque converter is not engaging. As a matter of fact i never felt or sense that drop in RPM's.
Talking to a couple of friends and driving their cars i can geel that drop in RPM after the 4th is engaged, mine does not drop and 4th is engaged at around 45-47 MPH. Where should i start checking? Truck is a M1123 with the GEP turbo engine swap.
I never thought about it before but now worries me.

 

[Dieselmeister]

Could be as simple as a bad wire, or bad or disconnected sensor. First, start by pulling the transmission error codes to see if they point at a specific error. Look at TM 9-2320-280-20-1 section 2-35 and the attached document. In my case it was a bad TPS signal.

 

[REF]

if the trans light comes on with the start switch and stays on with the engine running, you probably don't have an RPM signal from your engine. The N/A engine had a sender where the turbo now sits, The turbo engine has the sender in the left lower side of the timing cover. you will need to extend the connection to reach the new location. look for a 2 pin sure seal connector under the dog house on the drivers side coming out of your harness about the same height as the dash. If there is nothing plugged into it that's where I would start.

 

[Retiredwarhorses]

50% of the time TCC lock up not working is a bad brake switch, the other 50% is not adjusted correctly.

 

[Gcelevator]

if the trans light comes on with the start switch and stays on with the engine running, you probably don't have an RPM signal from your engine. The N/A engine had a sender where the turbo now sits, The turbo engine has the sender in the left lower side of the timing cover. you will need to extend the connection to reach the new location. look for a 2 pin sure seal connector under the dog house on the drivers side coming out of your harness about the same height as the dash. If there is nothing plugged into it that's where I would start.

Thank you. The TC light only comes on while run switch is open but after start the light turns off. The RPM sender is connected to the fron of the engine. I remember splicing those wires when i receiv3d the new wiring harness from steve.

 

[Gcelevator]

50% of the time TCC lock up not working is a bad brake switch, the other 50% is not adjusted correctly.

Thank you steve, i have to look into that. I remember long time ago i was plying with the switches as my stop light never came on however i never heard the torque converter engaging. I will check on this tomorrow.

 

[Gcelevator]

Could be as simple as a bad wire, or bad or disconnected sensor. First, start by pulling the transmission error codes to see if they point at a specific error. Look at TM 9-2320-280-20-1 section 2-35 and the attached document. In my case it was a bad TPS signal.

Thank you. Yes, have to start troubleshooting starting with codes, if any present. Will check and report back.

 

[Mogman]

Thank you. The TC light only comes on while run switch is open but after start the light turns off. The RPM sender is connected to the fron of the engine. I remember splicing those wires when i receiv3d the new wiring harness from steve.

Have you checked for codes? not all codes turn on the light

 

[Gcelevator]

Have you checked for codes? not all codes turn on the light

Hey Mog, yes i just checked for codes and only 12 (1 flash then 2 flashes) indicating 12 volts. Nothing else. I am going to double check on the RPM sensor as i recently replaced the AC lines and saw a conector on the rop of the transmission and i remember i had to extend it for the engine harness but now i am in a limb and don't remember if i did it for the transmission. Will check into it and report back.

 

[Mogman]

Hey Mog, yes i just checked for codes and only 12 (1 flash then 2 flashes) indicating 12 volts. Nothing else. I am going to double check on the RPM sensor as i recently replaced the AC lines and saw a conector on the rop of the transmission and i remember i had to extend it for the engine harness but now i am in a limb and don't remember if i did it for the transmission. Will check into it and report back.

It will flash 12 three times to show it is in diagnostic mode, then if there are no codes it will flash 12 a forth time and then stop, if there are codes it will flash each code three times after the first three 12s then when there are no more codes it will flash 12 one last time then stop.
I have found some do not wait until the full sequence is finished.

 

[Gcelevator]

It will flash 12 three times to show it is in diagnostic mode, then if there are no codes it will flash 12 a forth time and then stop, if there are codes it will flash each code three times after the first three 12s then when there are no more codes it will flash 12 one last time then stop.
I have found some do not wait until the full sequence is finished.

This one just flashed 12 several times more than 5 times until i stopped it myself. Tryied twice, the same outcome. I will check for the RPM wires on the transmission.

 

[Mogman]

Do you know if you have the old style TCM or the newer style PCS TCM?

 

[Gcelevator]

Do you know if you have the old style TCM or the newer style PCS TCM?

I just left my office, as soon as i get home i will double check and snap a picture and post it. Any specific way to know?

 

[Mogman]

The PCS TCM says PCS on it and has a 2100xx part number.

 

[Gcelevator]

The PCS TCM says PCS on it and has a 2100xx part number.
View attachment 917127

Mogman, here are a couple of pictures of the transmission box.

 

[Mogman]

No pics, does your truck have a tach?

 

[Mogman]

This is what the original TCM looks like, it has a small cover that can be removed to get to the PROM.

 

[Mogman]

I don't know how to decipher the information on the TCM housing cover, and the TCM could have been changed at any time.
If you had issues with any of the inputs like the ESS (engine speed sensor) you should have a code and also without that data it would not shift correctly if at all.
The first thing I would do is what RWH suggested and check the brake switch, which should also give a code if bad....
The trans side of the switch should be closed when no brakes are applied and open when the brake is applied.

 

[Gcelevator]

I don't know how to decipher the information on the TCM housing cover, and the TCM could have been changed at any time.
If you had issues with any of the inputs like the ESS (engine speed sensor) you should have a code and also without that data it would not shift correctly if at all.
The first thing I would do is what RWH suggested and check the brake switch, which should also give a code if bad....
The trans side of the switch should be closed when no brakes are applied and open when the brake is applied.

Yes, the bolts on top of the cover are a no go. I put some PB blaster on it and will get back to it in a couple of days.
Meanwhile, i believe my issue is this one, wries 97A and 97B were never connected. Go figure. I will have to splice them and get them in place.
I remember i had to extend the sensor in the front of the engine to connect below the fuel filter however 349 and 359 are connected to the engine speed sensor 359 being the transmission selenoid.

 

[Gcelevator]

No pics, does your truck have a tach?

No tachometer on this truck.