4th Gen - torque converter/cruise control issue

[riverwolf]

I first noticed the issue several years ago, but recently did road trips to Atlanta and back and then to the NC Smokys...enough hilly terrain to confirm the behavior.

On my June '03 build, the torque converter will unlock while going downhill...makes sense to some degree since the wheels/transmission need to turn faster than the engine for the given load. Problem is, if running on cruise control, it'll never relock when the road levels out or starts uphill again. Driving manually, there's no problem...TC stays locked uphill and either relocks after the downhill section or never unlocks at all while the throttle is being feathered.

I'm pretty sure I've seen this discussed in the past, but can't find anything using Search. Has anyone observed this on later years? I'm hoping maybe Toyota fixed the bug in whichever control unit software won't allow the TC to relock while under cruise control.

How much extra wear on the transmission is there from running unlocked at 70mph in hilly/mountain terrain? Am I being too OC trying to keep the TC locked by not using cruise when this starts happening?

-Brent

 

[JP4RNR]

How do you test the lock-up feature? On the older transmissions lockup would occur at a certain speed and if your RPM's did not fluctuate when you took your foot off the accelerator and then put your foot back on then you knew lockup was engaged.

On newer transmissions when you take your foot off the accel. pedal the lockup I heard disengages if you are coasting

 

[riverwolf]

How do you test the lock-up feature? On the older transmissions lockup would occur at a certain speed and if your RPM's did not fluctuate when you took your foot off the accelerator and then put your foot back on then you knew lockup was engaged.

On newer transmissions when you take your foot off the accel. pedal the lockup I heard disengages if you are coasting

Torque converter lockup is automatic. Based on a number of parameters, the computer decides when/if to engage the lockup.

Observing lock/unlock status is easy if you set the cruise and make a mental note of the tachometer reading. For instance, if I set cruise at 70 mph, my locked RPMs will be about a needle's width above 2000. After a while of being on cruise, I'll check RPMs and find them up around 2300...indicating the TC has unlocked. I can cancel cruise and resume and return to the locked status of just over 2000. Lather, rinse, repeat.

In the situations I've been observing, the TC has no trouble staying locked with cruise on going uphill, it's the downhill side that caused it to unlock as the wheels/transmission are now spinning faster than the engine needs in order to maintain set speed. That in itself isn't an issue, but the fact that it won't relock under cruise control is the problem. I think there's a bug in the software, at least on 2k3 models, that won't relock the TC once the parameters have stabilized. I'm trying to determine if this bug has been fixed in later models.

-Brent

 

[Methodical]

interesting. I too observe my transmission status a bit too much and haven't seen this phenomenon. I have a 2004 V6.

 

[RickyCRX]

This annoys me to NO end on my '03 V8 4Runner. So much so that I almost never use my cruise control. Running with the TCC unlocked causes excessive heat to build up in the transmission and will degrade the fluid (even though I run Amsoil synthetic). It also burns more fuel since you're turning a higher RPM.

If anybody has an answer to this, I would greatly appreciate it. If you have a newer V8 4Runner, please try setting your cruise control at 70mph on level ground... Your tach should be right around 2,000rpm or so.. After a good downhill run and the terrain levels back out, check to see that your tach is still at 2,000 rpm or so. If it's 200 rpm higher, then it is not locking back up.

I'd be really gracious to anybody that comes up with a solution to this problem (design flaw).