Lockout torque converter circuit

Tiny
PORKCHOP68
  • MEMBER
  • CHEVROLET TRUCK
I have a 93 chevy 3500, 7.4L. 4L80E trans. The problem is @ about 2500 R.P.M. Or between 60 & 65 M.P.H. The torque converter disenguages, In @ out. From 98% to 0%.
Have changed numerous sensors. Ask everybody I can. Nobody knows. I`m a truck & equipment mechanic and it`s aggrivating not to figure this out. With help from trans. Buddy.I found the signal ground from the computer to the converter clutch solinoid and @speed when the problem occurs by adding a ground to this circuit, it stops & does fine.
Have just about pulled my hair out. Sure accept any
suggestions. This is my service truck, and i`m still running it. But would rather fix it.
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Sunday, November 18th, 2007 AT 9:32 PM

3 Replies

Tiny
TOBYU
  • MEMBER
By adding ground to the circuit you are probably engaging the TCC so you don't get the in and out.
The system is more than likely. Most are. Designed to have voltage to the TCC solenoid all the time and the ground is switched to make things happen.
Have you replaced the VSS speed sensor? I also think the 93 will only engage the TCC if engine temp is above 140 degrees. So make make sure your gauge goes up on the dash and more importantly check or replace the engine coolant temp sensor that only tells the ECM what temp the coolant is.

If could also be a bad ECM. If it kicks in and out. Then the ecm is telling it too lock. But not keeping it locked.
It would be nice to know if the ECM is calling for lock up all the time. Even when the TCC unlock and it kicks out.
You could tap a test light into the pin at the wire on the ECM that engages the TCC. You can try your ground wire that you know engages it.
Go to that pin on the ecm and see if your test light stays on. Or on and off with the in and out.
This will tell if it is internal ECM or if the ECM is doing the right thing. But the signal is getting lost down the wire somewhere. Could be loose connection at tranny connector or frayed wire.

There also might be a signal wire form ECM to TCC that is not that same ground that you would need to check.
Get a TCC wiring diagram.
Good luck.
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Monday, November 19th, 2007 AT 12:39 AM
Tiny
PORKCHOP68
  • MEMBER
Have checked and swapped ECM same thing. Have changed speedo sensor, TPS, Brake light switch etc.
Haven t temp. Sensor, the guage works but there are two sensors, one on either side. I would think signal to TCC is ok because if it is not connected it won t shift into overdrive. Hope I haven t left anything out, but if you think of anything else, my ears are open. I really appreciate the input I ll give it a try. Nobody seems to have heard of this before but I know it can t be the only one, and can t see it being un fixable. It was made by a man, it can fixed by one. THANKS, Porkchop.
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Monday, November 19th, 2007 AT 7:46 PM
Tiny
PORKCHOP68
  • MEMBER
I replaced temp. Switch, no change. Guage sensor is ok. Do you know if this is a switch or a sensor. And if it is a switch is it normally open or closed? Thanks for your help!
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Friday, November 23rd, 2007 AT 2:07 PM

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