Possessed Torque Converter--Random TCC "Unlocking"

[Faust]

First of all, the Search button has been a dear friend of mine for the last 2 months that I have been an Explorer owner. I thank the author of the "3,000 rpm tach fix," and also those who contributed to the "EGR 558" and other EGR code fixes.

That being said, I still cannot find any information on a similar TTC problem as I have.

The truck is a 1994 XLT 4x4 auto with 158,000. It has been well maintained with only one owner. The trans has been flushed at 100,000 and it runs fairly well (still get a random 558 even though everything has been replaced).

THE PROBLEM:
I can run the truck and it will give me shifts 1-4 without slip or hesitation. USUALLY I get the torque converter 500ish rpm drop at 55 mph. This can be dismissed with more throttle or a tap of the brakes, then it will resume, like a normal truck. BUT after some time (cannot get an exact time) the converter will unlock making me drive at 2,500-3,000 and will not ever go back. I can then pull over, put it in park, turn it off, immediately start it back up (no cool-down) pull back on the road and have my 2,000 rpm cruising locked up truck for another, eh, 5 miles, then it comes back out again. The fluid is clean and topped off. No other CEL codes except 558.

Any thoughts? Is the torque converter just shot?

 

[MrShorty]

Here's what I think I would do:

1) Get a wiring diagram so you can see where to put the voltmeter.
2) Put your voltmeter on the TCC solenoid so you are measuring the voltage drop across the solenoid.
3) For practice, run the output state test (see my notes on pulling EEC-IV codes) so you can see the voltmeter switch states from on (12 V drop across solenoid) and off (0 V drop across solenoid).
4) Test drive. When the TCC unlocks, see if the computer has changed states to match the TCC, or if the PCM is still commanding lockup but the transmission is not obeying.

If the transmission is responding to the PCM's command, then you can continue looking at sensors/wiring/etc. to see what is causing the PCM to stop commanding lockup. If the transmission is not responding as commanded by the PCM, then the problem is likely something hydraulic/mechanical inside the transmission.

 

[Faust]

SOLVED: Random TCC unlock

Howdy,

My 1994 XLT 4x4 auto PCM was commanding the TCC to unlock after driving 10-15 minutes. I found this out through Mr. Shorty instructing me to back probe the PCM signal wire for the clutch. The voltage dropped so it was a sensor problem NOT a trans problem. I only got a CEL ONCE with a 186 code, and that wasnt until driving the truck for 40 miles straight.

After reading on Napafix how to best test the MAF I did so with my buddy's Verus data computer/scanner. Napafix offered more insight than my crappy Chilton's book. At idle, the MAF should have 1 volt. Then, when you punch it hard and quick it should smoothly graph up greater than 3 volts. I tried this with my DVOM, but it was not easy to see the jagged jumps that my (bad) MAF was producing and my idle voltage (according to the Verus) was .6-.9 then at the punch only 2.3 V.

So, a $70 trip to O'Really?s and ten minutes made the truck shift 115% better and made me a happy camper. On my 600 mile trip this weekend I got 17.6 MPG with mixed driving.

Hope this might help someone else. No/Random TCC + 186 = MAF for me.

PS. Thank you Mr. Shorty for your patience.

 

[MrShorty]

Glad you got it figured out.

 

[Turdle]

I merged your posts into one thread, in hopes it will help others with the same issue.