My short question is: why would the TCC lockup NOT function and NOT throw any codes and/or make the OD light start blinking?

What follows below is long, sorry, but wanted to be thorough.

The truck is a 1992 F250 4x4 7.3 Diesel with an E4OD. This truck belongs to a friend of mine and we've been trying to diagnose the source of a blinking OD light and code 62 (TC slippage). I'm fairly familiar with this trans and realize that the slippage can be due to the solenoid, the valve in the pump, or the clutch mechanism in the TC itself (or some other clutch pack in the trans slipping, but I don't think that's happening). So over the weekend I set out to carefully diagnose the problem using an online shop manual I found. Here's what I did:

1. I first replaced the solenoid wiring harness (it was ratty looking, but appeared in tact). After replacing this I cleared the codes and took it on a trip on the highway. Sure enough, after a few miles, the OD light started blinking so I took it back home and got the code 62 again.

2. Line pressure test (all levels fairly close to spec)

3. Stall speed test (all close to spec in all ranges)

4. Electrical tests (TCC solenoid was fine, the fluid temp sensor was fine, everything checked out)

5. Grounded out the TCC solenoid wire with trans in gear, engine did NOT stall, but slowed down a bit. This signaled clearly to me that the TCC solenoid is working, but the clutch either isn't getting enough fluid or is burned out so it's not engaging.

6. Lastly, I wanted to see when/if the TCM was signaling the TCC lockup, so I hooked up a continuity tester between the TCC lockup wire (purple/white) and ground, cleared the codes, and took it back on the highway. I expected to hear the continuity BEEP when I got up to highway speed, followed by the OD light flashing again. To my surprise, I never heard the beep and the OD light never came back on. The truck runs great and shifts fine, and the OD will turn off via the button as it's supposed to.

I've now driven it for several highway miles and the OD light still has not come back on, but I can tell that the TCC lockup is NOT happening. The PCM gives no codes, all I get it the "system OK" code.

It seems like if there is something preventing the TCC from locking up, it would throw a code, right?

I should also mention that the VSS is new and the TPS has been checked and is within spec.

If you've made it this far in my post, thank you for reading all of that, and thanks in advance for any insight you can offer.

 

My SWAG, based on years of experience with this, is that the torque converter clutch apply piston has a crack and is bleeding pressure. The conclusive test was grounding the wire with the trans in gear and it slowed the engine, but did not stall it. That means that there is enough capacity on the clutch to add load to the engine, but not enough to stall it. That test alone would be enough for me to replace the torque converter.

As to why it isn't setting a code now, I don't know,

 

Mark, thanks for your reply. I think you're right about the TCC.

I just drove it around again and noticed that the coolant temp gauge appears to be malfunctioning. It always shows cold. This is a new symptom. I'll bet that explains the no lockup attempt and no blinking OD light. The TCM probably won't try locking up the TC until the engine is heated up. What do you think?

I'm going to replace the temp sending unit and report back.

 

Yep, it was the coolant temp sensor that kept the TCC lockup signal from happening. Interesting to know that the TCM uses the same sensor as the gauge (or at least it appears that way).

So everything's basically the same, the OD light comes on again, no TCC lockup.

Mark- what do you think the chances are of this being related to the valve in the pump or the seal on the pump stator? If I recall correctly, if that stator teflon seal is bad, fluid will leak around it and the TCC won't apply correctly. I guess I'll know when we pull the tranny and have a look.

 

Ye, if that seal is bad the converter won't lock. The seal is more robust than the converter. My bet is on the converter, but it could be the seal.

 

Well, I had reason to believe that the seal was not correctly installed. I knew, because, well, I helped install it, and we did not have assembly lube with us at the time, but tried using oil to keep the seal scrunched in while we pushed the converter in.

And my suspicions were correct. I got the tranny out today and that seal is GONE. It must have gotten caught up when we put the converter in, then pushed out of place. Doh! Hopefully putting a new seal in there will do the trick. Just left wondering where the bits of the old one might have gone.

Chalk this one up to plain old boneheadedness.