1992-1993 TCC lockup mod 4L80E

[WarWagon]

The oddball year that the PCM (ECM) computer controls the transmission only.

The "brown wire" Heath mod does not apply to all years and there is really no reason to go outside the cab to mod or tap PCM wires.

To do this mod pull the glovebox to access the computer. Look on the right/passenger side connector for a tan wire with a black stripe. (F&%$ going under the truck to look at or cut the transmission wires. 1994 on up may have to do this and there are other guides for newer years that do not go under the truck.)

Cut this wire.

Get a two position switch, SPDT. Select1, Center, Select2.
Connect:
ECM side to a side of 3 way switch.
Ground to another side of the 3 way switch.
Transmission side to the center pole of the 3 way switch. Transmission is of course the wire you cut not going into the ECM connector but the body side.

You will throw a TCC open/short code. No Service Engine soon light will come on.

Optional:
To eliminate this code use a resistor or relay with a surge diode from a positive voltage source tapped into the ECM side wire. This keeps a voltage to the ECM pin, but, will limit current when the ECM grounds the pin. The ECM will not see an open circuit and no code.

So relay coil and diode stripe side to positive voltage. Relay coil and diode to ECM pin.

Reference:

http://www.jegs.com/InstallationInstructions/100/151/151-1030390.pdf

 

[JiFaire]

iirc, you splice into Pin C11 of the PCM

 

[midniteplowboyy]

I used an old school floor mounted dimmer switch, just an option if you wanna use your foot or running out of room on your dash for switches and gauges.

I'll check the pin number, if I remember tonight at work.

I agree WW, makes no sense at all to go under the truck, to much work.

 

[handcannon]

I recently did this mod to my 94 OBD-1 truck. I removed the glove box and did the wire work under the dash instead of under the truck.

I did do something a bit different though. I used a DPDT switch. One pole was for the TCC lockup mod, the other was for colored LEDs

to let me know at a glance which mode I was in (it's a memory thing). I ran 12v to the center tab, a green LED on the tab that matched

to the stock TCC position and a red LED to the lockup position. I put the switch/LEDs in one of the three removeable plates below the

heater/AC control panel.

Don

 

[chessie 6.5]

I did mine behind glove box. (94). However, I did check wire color at trans plug as my colors didn't seem right. Used a switch with center off to disconnect lockup if desired for some reason. I installed switch into one of the blank switch spots on right side of dash panel.

 

[WarWagon]

The LED idea is awesome.

Results after towing into a headwind and up and down some good grades:
Before:
Trans temp 250+ Gauge quits at 250.
No speed gain on some hills.
No real compression braking - engine drops lots of RPM when TCC unlocks.

After:
Trans temp below 250, around 210 - 225.
Would gain speed on some hills.
Did not have to shift to 3rd and let up on throttle to lock the converter and sneak up on power attempting to stay under the point it gets unlocked by the computer.
Could use the engine for compression braking into 2nd.

Flick switch and Tach drops RPM. :agreed:

 

[TxZX6R]

Will this at all damage my tranny in my 94 2500? I pull a trash trailer 16' long with a 6'1" tall cage and itsl ike 5' wide. Average weight pulled is like 4400lbs with lots of stop and go's. Also, this just kicks it in and out of overdrive as needed right?

 

[BigArt]

Here's a quick drawing of TCC mod I made for my '95. As well as hi idle mod. Not sure it will help. Good luck.

Art

 

[boss4457]

i am confused on how to install this switch can i do it with a regular 2 pole switch. What will happen if i dont cut the wire but just ground the wire out when the switch is on will that work?

 

[WarWagon]

I wrote this over 8 years ago. No Zombie thread points: just an update. I have since burned up 3 transmission Torque Converter Clutches and 3 Overrun Clutches. IMO the only relevant weak points of a 4L80E. This said I do not recommend this mod on a stock transmission because the OEM Torque Converter Clutch isn't strong enough to hold the diesel torque at low MPH. The overrun clutches are small and really can't hold with the TCC locked for compression braking. They "surge" during compression braking as they are slipping and quickly burn up.

I also found the oil coolers were messed up putting hot oil through the air to oil cooler first then heating it back up in the radiator oil to coolant trans cooler. Radiator first then air to oil cooler gets me cooler running trans temps.

I use a triple disk Yank converter to lockup down to 35 MPH and do not compression brake in manual 3rd. Can't compresion brake as the overrun clutches are and have been toast for a long time.

The Mod itself "opens" the TCC wire from the ECM and grounds the trans wire to lock the TCC. ECM's rather see an open than a short because shorts generally trigger limp mode. You are welcome to tap the wire and ground it to see how the ECM handles it.