sfrolich

I think my transmission computer unit has a bug or something. Has anyone seen the torque converter occasionally NOT lockup when using cruise control? I can make this happen every time on my 4Runner. We ought to see if this happens with all 03’ 4Runners (I have the 5speed v8) because if it is, this is a major fuel mileage problem.

Here’s what to do:
1) Go down a level freeway at any freeway speed, say 60MPH
2) Set the cruise control
3) Note the exact speed and RPM’s down to the 100th; you will need this reading to compare later
4) Now decelerate the 4Runner with the cruise control (not the brakes) until you see the RPM’s drop abruptly about 250 – 500 RPM’s. This is when the torque converter unlocks itself
5) Stop decelerating
6) Using the cruise control, bring the speed back to the same as before.
7) Now see if the RPM’s are higher. Right here mine is since the torque converter is not locked.
8) Now put the transmission into 4th gear and then back to 5th. Now the RPM’s ought to be where they originally were.

Please let me know either way if you go through the 8 steps. I’m bringing it into the shop in a couple of weeks and I’d like to know if this is a problem across 4Runners or just mine.

The weird thing is that I had this very same problem in my 98 5.9L JGC.

Thanks,
Scott

richardyc

I hope this is an isolated case, but if not, prepare to hear "If they all do that, so it must be normal."

BT17R

Interesting glitch, and great writeup. I hope the dealer understands something as arcane as this. Your best bet will be to drive another fresh one off the lot for comparison. I'd like to help with the diagnosis, but I almost never drive on a freeway. I'll check next time I do. Good luck.

Good Times

since i'll be driving up to san jose tomorrow for the weekend (from LA), i'll give it a try.

but i'm thinking that would be the case right? figure if you slow down enough it'd end up going down a gear (say 4th) and then if you accelerate it'll stay in that gear unless there is a significant change in speed. not sure if this makes sense but i can see why it would happen... i'm thinking if you go fast enough it'll go up a gear eventually (my thinking). prob has to calculate and see if you stabilize at the current speed before it changes gear!?

not sure, now i'm confusing myself i'll try it tomorrow none the less... i'll report back when I come back on monday

sfrolich

Well that isn't exactly what's happening here. My 4Runner stays in 5th gear but disengages the torque converter. All you need to do is decelerate 5 MPH. If you going from LA to San Jose on I5, try it at 75MPH. Use the cruise control to go down to 70MPH. While you are slowing to 70MPH, you ought to see the RPM's do a quick drop of 100-200 RPM's when the converter unlocks.

Now when you hit the shifter to 4th, the RPM's will rise letting you know that it isn't in 4th already. Then put it back into 5th and the converter will lock. Remember to do this on a flat highway.

From freeway speeds, I don't think the tranny will drop down to 4th gear until 45MPH or less so that's defenitely not what I'm seeing.

Let me know if anyone needs more clarificaiton on how to reproduce this problem. Can you tell I work in the computer field??

Scott

Good Times

scott:

okay that makes more sense now i'll definitely try that out tomorrow and give ya back a feed back asap then!

computer field? nah what gave it away?!?!

lance

khaug

Scott, I just got back from an 18-mile midnight jaunt on I-96 to see if mine behaves like you report yours does (that's $2.09 worth of Mobil's finest premium at current prices here - I'll send you the bill :-) ).

Mine doesn't do what you report. Instead, when I've coasted down from 70 mph (2000 rpm exactly) to 65, seen the ~200 rpm sudden drop, then reengaged the cruise control, the truck will accelerate back to 70 with the converter still unlocked. When it reaches 70, it will briefly hold at 2200 rpm, then drop back to 2000 when the converter locks back up. I repeated this several times with the same result. I'd call this normal and expected behavior.

However, what my truck does do, is occasionally fail to return to converter lockup while towing my 4,000 # trailer at highway speeds in 5th. While towing, it's common for the torque converter to unlock when the truck encounters gentle grades. Usually it will re-lock when I've crested the rise. On occasion, though, it will remain unlocked even when descending a gentle grade. This forces me to resort to your ploy of manually shifting the tranny to 4th for a moment, then back to 5th. The converter will then always lock up.

The other thing I've observed is that the converter occasionally will apparently only partially lock up after unlocking, leaving me running at 2100 rpm and 70 mph in 5th. This one REALLY spooks me, as it implies slippage of the lockup clutch, which can't be a good thing. Again, this is cured by momentarily shifting to 4th.

I've not complained to my dealer about these anomalies, as I have no confidence in the service staff's ability to deal effectively with something this subtle. If you do complain, please post back and let us know how you make out. BTW, my truck is an early (10/02) build model with 16K miles at present.

Good luck.

sfrolich

Well it sounds like there might be some kind of problem here. That is scary about a "partial-lockup" of the converter.

I'm not towing anything and I can even make it happen on a slight downgrade every single time.

I'll bring it to the shop in the next couple of weeks and give and update.

If anyone else wants to try that and report back that would be great.

Thanks,
Scott

TechWrench

Very interesting post, I will have to try this on my '03 V6. But I have one question. You said in your post that you noted the RPM dropped several hundred when the converter unlocks. That sounds just opposite of what one would expect. Because of the slight slippage in the torque converter when it is not locked, the RPMs at a set road speed should decrease when the converter is locked, and then increase when it unlocks. It almost sounds like the converter is not locked in the first place, and when you decelerate slightly, it then locks up and the RPMs drop because of the direct connection through the converter.

TechWrench

All, While researching transmission info for another thread, I came across the following site with info on the Electronic controls for the transmission.

http://www.autoshop101.com/forms/h16.pdf

On page 14 of this, it explains reasons why the Electronic Control Unit (ECU) will cancel converter lock-up. One of the reasons is if the Vehicle speed drops about 6 mph or more below the set speed while the cruise control is operating.

I think this is what sfrolich is experiencing. As I said in my earlier post, if the rpms increase but the road speed doesn't, this indicates that you no longer have lock-up through the converter.

PistonSlap

Sounds like a neat trick to impress your friends, but I don't think it is a glitch. You are using the accelerate/decelerate function of cruise control out of the normal operating use. It is designed to adjust your speed slightly and not a sudden drop of speed. You should also not use the resume feature for sudden accelerations to get back to the speed that you were previously at. This is why you last speed cancels when you drop below 20mph.

My guess is that by using this gimmick method, you are not getting the lockup clutch to engage. This would account for the rpm change to maintain the same speed. Unless you can duplicate this by using cruise control and the pedal properly, I would say that there nothing wrong.

sfrolich

Sorry for not positing sooner.

In regards to TechWrench about the RPM drop being reverse. What I was trying to say is while having the cruise control decelerate the car, it will drop suddenly when the computer decides to unlock the TC. You would expect it to drop since the engine is putting no load on the transmission. If the TC stayed locked there would be this nice linear RPM drop.

Now once this unlock has occurred, no matter what you do it will never lock the converter again; period. I sat there and waited minutes to see if it would but it doesn’t. Keep in mind this is while being at freeway speeds and having the transmission stay in one gear the whole time (5th). Here is a simpler method to try and reproduce this.

1) Engage cruise control at 65MPH on a flat road (note exact RPM speed)
2) Decelerate using the cruise control for 5 seconds then wait 10 seconds
3) Using the gas pedal, slowly increase speed to 65MPH (note exact RPM speed)

In my case #3 RPM will be higher than #1. The only way to re-engage the TC is to shift into 4th then to 5th or turn off the cruise control.

Thanks for everyone’s input,
Scott

tom4416

You should never tow in 5th gear - read the owners manual and talk to Toyota. You are lugging the engine as well as overheating the transmission. Toyota recommends always towing in 4 on the 5spd and 3 on the 4. On a trip to Florida towing about 2200lbs, I stayed in 3rd and got 16.2MPG and the truck never had to downshift for hills. When I tried towing in 4th w/overdrive, the mileage went down and the transmission was hunting on hills and the engine was even further out of its powerband. Several Toyota techs have really stressed this issue to me so I think maybe it is legitimate, IMHO.

jjcobra99

The original post makes perfect sense, and I understand what you're saying...except when the TC unlocks, the RPM will rise, not fall. I think TechWrench nailed it though.

BTW, I too have towed in 5th. I know what the owner's manual says, but I just can't can't see towing down the freeway for extended periods of time at 75+MPH. In the mountains, I went down to 4th and 3rd. I don't see where it will hurt it as long as there's not TOO much of a load on it. If I was towing near max capacity, I could understand not using 5th. I was probably only pulling about 2000lbs though, and it did fine. No problems at all.

TechWrench

sfrolich, The site I mentioned in my earlier post with the information on the electronic control system for the transmission made it very clear that the ECU would disengage lock-up if the road speed dropped more that six mph from the 'set' point. I think the set point is the key here. I have not as yet been able to try any of this on my SR5, but I might suggest one further experiment to you. After you have set the cruise at lets say 65, and then used the decel function to reduce speed to 57, the lock-up should disengage. At that point, why not try hitting the set button again. I would be interested to see if the lock-up would then reengage at the new set point. What I am guessing here is that because you have first used the decel function to reduce the road speed below the six mph limit, the lock-up is disengaged and the cruise control 'brain' is now holding the speed at this temporary setting. And when you use the gas pedal to return to the original set point speed, the cruise control 'brain' still wants to hold the 57 mph speed. I would bet that if you released the gas pedal, the speed would return to 57 because it was the last command it had. So even though you 'forced' the speed up to the 'set' point of 65, the cruise wants to go back to 57 and therefore the command to disengage lock-up isn't removed. I don't remember if you mentioned what happened if you used the accel function to return to the original original set point instead of using the gas pedal. I wonder if that would allow lock-up to reengage?

sfrolich

All good points. I'll give it a try the next time I drive.

Thanks,
Scott

sfrolich

Actually this is impossible to do. Pushing up on the CC lever is eiher accelerate/resume and down is decelerate/set depending if the CC is engaged or not. So decelerating using CC is actually setting a new speed. Hope that makes sence. Go look at the CC lever and you'll know what I mean.

Scott

TechWrench

You are right. Because of my driving habits, I seldom find the need to use the cruise. So after I made that post, I checked my SR5 and realized I was confusing its CC with my old Accord. Sorry about that. I am taking a long day trip this weekend, and will have plenty of time to play with the CC. I will try to duplicate what you are seeing, and think on it some more. Will get back then.