Another Torque Converter no-lockup problem

A bit of back ground.
1989 AW4 4.0

I have had problems with the coolant temps rising to 235+ at speed and tracked it down to the torque converter not locking. The tranny shifts though all gears just fine while driving. Manual shifting works too.

I have been on a couple of trips after the swap where the coolant temp did not rise.

Last year I swap an AW4 in for the old BA/10.
It was a straight swap out of my 1990 donor. Swapped the Engine bay wire harness, TCU and TPS.

Put light on C14 to ground. No light.
Put switch with power to C14. TC lockes when power applied. (TC works)

I have read many threads on the TC lockup and tested the TSP and TCU.

The TPS Look OK.
Pins A - D 4.6 volts
Pins B - D 3.9 -> 0.4 volts smooth transition

TCU
This look questionable to me but....

Key on Motor off
Pin Volts
C3 5.8
C8 0.8 Shifter in 1-2
C9 0.0 Shifter in D
C10 11.04 Brake off
10.96 Brake on
D1 5.5
D2 4.7 throttle closed
1.1 WOT
D3 0.8
D16 12.6

Key off
D14 11.4

Resistance - unplugged
C14 13.9
C15 13.9
C16 13.7

Resistance across brake switch
brake on inf.
brake off 0

C10 to brake switch 1219 ohms (set at 2000)

Resister by TCU between C10 Lt. Blue/Yellow to yellow ECU
1205 ohms

I have hit the limit of my electronics abilities with this one.
To me it seem that the voltage on C10 is causing the TCU to think the brake is on and not lock the converter. Any ideas why it has the voltage with brake off?

The volts on C9, C10 are off the values given at (http://www.transonline.com/transdigest/magazines/1997-10/Shift Pointers/index.html). Unless you think those are related I'll skip that for now.

It's a little pricey but have you tried amsoil tranny fluid and antifreeze? You'd be shocked at how much cooler it runs. 2000 xj stock ran 15-17 degrees cooler after replacing these two fluids, used an infrared thermometer.

dkmum1 said:

It's a little pricey but have you tried amsoil tranny fluid and antifreeze? You'd be shocked at how much cooler it runs. 2000 xj stock ran 15-17 degrees cooler after replacing these two fluids, used an infrared thermometer.

Click to expand...

With the slippage in the TC it would not make enough difference. When I force the TC to lock I did not have the heat problems. I need to solve the no lockup issue.

Yes, C10 staying high will prevent the t/c from locking up. When you did the tranny swap, did you install/wire the extra switch at the brake pedal? If you had cruise control, the switch might have already been there. It's white and located high up near the top of the brake pedal arm. That switch has also been known to gunk up and stop working. It can be popped apart and cleaned.

Looks like this:

Yep brake switch in installed.

But I did find the problem. It was related to the brake switch. There is another connector that I missed. The old harness had a 3 pin and the new harness had a 6 pin. I had connected the three wires before but no difference. I think that was due to a gummed up brake switch.

Now that I had the brake switch in and cleaned up I rigged a connection on all three wires again. Bingo!

I'll leave the TC lock indicator light in place to I can enjoy it....

To bad the FSM version that I have does not list all the connectors. That would make life too easy.

To all:
Thanks for the help. All the threads on colling and TC issues I researched were invaluable.

Wisdom comes from experience. Experience comes from mistakes.
Wisdom can give you a headache!!!