Solved TCC locking/unlocking

[elgoathead]

During moderate acceleration it sometimes goes into lockup, then unlocks momentarily before locking back in.

This doesn't usually happen during more spirited acceleration (wait, did I just use the word "spirited" to describe the 4.0 OHV?).

Furthermore, I can make it behave by reducing pressure slightly on the accelerator pedal when initial lockup is achieved.

It's as if it can't handle the load, so it cycles back out.

What's up with this?

Application: 1996 4.0 OHV 4WD

 

[my98nnj]

Yes.

 

[imp]

During moderate acceleration it sometimes goes into lockup, then unlocks momentarily before locking back in.

This doesn't usually happen during more spirited acceleration (wait, did I just use the word "spirited" to describe the 4.0 OHV?).

Furthermore, I can make it behave by reducing pressure slightly on the accelerator pedal when initial lockup is achieved.

It's as if it can't handle the load, so it cycles back out.

What's up with this?

Application: 1996 4.0 OHV 4WD

Positive this is the TCC disengaging, and not 4th. gear dropping down to 3rd.? Check for trouble codes. Suggestive of problem either with TCC solenoid or the TCC itself, lastly, valve body problem. imp

 

[elgoathead]

imp,

Yup, I'm positive it's the TCC unlocking. I keep the OD turned off most of the time; it happens when the OD is on as well, but it occurs before I'm going fast enough for it to shift into OD.

A scan of the ECM reveals no DTCs: the computer thinks everything is hunky-dory.

However, something came to me today; while the engine overall runs quite well, I sometimes sense a lean condition during light/moderate acceleration; it is quite solid an hard acceleration. Could it be that more throttle opening is required to overcome that, being just enough to force an unlock? Perhaps the problem lies not with the tranny at all, but rather it may merely be a symptom of an issue with the engine. If this is true, it must be subtle, because, again, no DTCs are recorded.

Thanks... Mike

 

[elgoathead]

Update

The problem, as it turns out, was not with the transmission at all: it was vacuum leaks.

I swerved into this by accident when I took things apart to replace valve cover gaskets.

The valve cover on the driver side had a rust hole the size of a pencil eraser where a bracket was spot-welded. The pcv valve was open always (it rattled but was unable to close). The egr supply tube nut was not fully seated, allowing gasses to escape and presumably allowing unwanted entry of fresh air. It looks like someone had worked on it and forgot to tighten this nut, and it rusted in that position.

Not only does the tranny work correctly now, but the engine is smoother and more responsive.

Note to self (again): Always look at the simple stuff first.

 

[Turdle]

Thanks for posting your findings. I'll mark this as a "solved". Maybe it will help other folks-