This is a sudden problem that started a couple weeks ago, everything worked perfectly until then. I was settling into cruise at 62 mph and the converter started unlocking, then locking, then unlocking, back and forth, in quick succession, this went on for 9 seconds or so and then went away.

To make sure it was not a misfire related thing, I used Edit and set all the misfire thresholds to the max, (3672 or whatever that max number is that GM used in the tables, just going from memory). Nothing unusal happened again until yesterday when the converter unlocked and locked one time for no reason at part throttle, 50 mph. Then the same thing happened today.

The car has 96,500 miles, SY3500 converter has about 75,000 miles on it, the trans is an FLP Level 4 with about 48,000 miles on it. Some weekend drag racing (We'll call it 150 passes on the converter and a few dozen on the transmission but not at all in the past 3 years and even then being only a 12.3x second car it's not like the drivetrain was straining it much.) Fluid is GM changed every 20,000 miles. It's due for a change this fall so I have not opened the pan almost 2 years to look inside.

At this point I'm trying to decide what to do with it. Which parameter is it in Autotap that you watch to see if lockup is being commanded? I looked through them but it did not jump out at me.

I was planning on keeping the car one more year. Which direction I take mostly depends on what is wrong with it. If any of the trans guys here have any ideas for me that would be very much appreciated. There's a local trans shop that does good work but I'm hesistant to take it there at this point, when I can't duplicate the symptoms for him. I have the stock converter sitting on a shelf in the basement if I need it but I'm not sure if it's converter or transmission or tuning.

I've checked the fluid level and I've checked that switch near the brake pedal, it seems to be properly adjusted.

 

You are smart for not taking it in until you can duplicate the symptoms. Something changed recently right? What has been done to the vehicle recently? Anything you can tell me is important, leave nothing out.

Based on what you stated we can rule out Misfires. And also I would say the converter is doing what it is being commanded to do. It could be mechanical but I don't think so at this point.

One important clue here is the comments about light throttle affecting the condition. If you can, go in and change the Release or Unlock tables to something like ... greater than 18% TPS. In other words we want the converter to stay locked up until you provide a significant throttle input. Then go drive it. That could tell us if the problem can be manipulated by the software.

I prefer to see initial converter lock up control enable tables to be set up something like this... No 3rd gear lock up... 4th gear lock up only above 55 mph, and TPS % set somewhere around 11% - 13%. This will allow the converter to lock up only at very light or slight throttle. That can be considered a base line for tuning it in... very dependant on converter and gear ratio vs tire size.

Try that and get back to us.

All the while pay very, very close attention to the Throttle Position Sensor! It could be defective and could easily create these symptoms... Lock up is very dependant on TPS!

Hope that helps.

g

 

Thanks very much for the detailed response. That gives me some things to do and check. Nothing at all has changed in the car in the way of mods or tuning for three years (except as I said I reset the misfire threshold after this started) The only thing I would add is another symptom. Was returning the favor of revving on a vette at a stop sign and I shifted from neutral to first and then hit the gas to leave the stop sign and first wasn't there or rather it had not yet engaged and so the rpms shot up, i backed off the accelerator, first engaged and I took off. I'm sure that didn't help the tranny any but this happened days after the first unlock lock bout. First time that happened but this trans (going back to the day it was installed) takes a full second and a half between the time you move the selector to the time it gets into gear...like going from park to reverse.

I'm going to examine those tables now.

 

This is how the normal mode TCC table reads (through 25%) vs TPS, it's all stock..

2nd apply is 255 across the board
3rd apply is 30, 30, 33, 40, 50
4th apply is 45, 45, 45, 48, 49
2nd release is 255 across the board
3rd release is 28, 28, 28, 28, 32
4th release is 41, 41,41,41,45

What are these numbers, mph?

So, exactly what do I change? I think I'll be changing third and fourth release to 255 through 18%? No wait, that doesn't sound right...?

Then on deleting 3rd gear lockup and 4th below 55, I change 3rd apply so something really high, like 100 or 254 or something all the way across (?) then 4th apply (looks like its set to lock at 45 which I kind of like for road mileage and road manners but i'm perfectly willing to change to fix this) I change the ones that are 45-49 now to 55, yes?

Then I do all this again in the cruise mode table?
I'm barely a hack so I just want to confirm before I screw something up.

 

Gilbert I think you are using a different tuning software than edit but does this sound right?

1) To disable 3rd gear lockup, set 3rd gear apply and release columns to 255 across the board. (essentially what they have done in second gear)

2) In Edit the tps table columns are 0%, 6, 12, 18, 25, 31.....To enable lockup only over 55 and tps in the low range near what you've suggested, set 4th gear apply to 55 for tps through 12, then to 255 beyond 12 (disabling all but light throttle lockup)

3) Set 4th gear release for tps 12 and under to what? 47? 51? Then above 12% it would be what, the same as 12% and under ? This particular row is the one I have the most confusion over, I guess what I'm afraid of is programming it wrong and it doesn't unlock when it needs to.

 

Yeah ok. Must be trade secrets.

I think I found the problem. Definitely found A problem. Noticed a surge that wasn't there before while I let it idle in the driveway while I was getting the mail. The PCV vacuum hoses were melted/worn completely through in 3 spots, resulting in a nice vacuum leak, letting unmetered air into the throttlebody. It's a wonder that it still ran. Replaced all of them and a fitting. Definitely more power and smoother idle...maybe too, my intermittant unlocking problem was related. I'm hopeful.

 

Well the vaccume leak could cause many isssues , including engine missfire so with any luck you have solved the issue

 

Put some in town miles on it today and no lock/unlock troubles yet but, while at a stop light, first gear did not engage, had no creep when I let my foot off the brake (as if it was in neutral). When traffic started moving I pushed the accelerator, revs went up a little and first finally grabbed. Not sure what to think. It doesn't slip (that I can tell) in first once you are moving. Thats twice that that has happened. Something still isn't right. But all the shifts feel good and firm.

 

You need to get it on a scanner and watch the data stream and see just what the PCM is comanding as far as shifts etc.

 

I wonder if your transmissions oil filter is full of lockup clutch material. I have seen this cause a neutral condition. Might be something to address.

 

I couldn't stand the suspense any more, so, I pulled the pan. Everything looks great. Fluid still looked new (has 18k miles since last change), nothing in the bottom of the pan but the usual film of material on the magnet. Nothing observable in the filter but fluid. I'll button it back up tomorrow.

 

Take and crack that filter open. The element inside it is kind of like a sock. Look inside it for signs of the lockup clutch.

 

Vince, what do you think? There is a black sliver on one side, I can't tell what it is but it's shiney. Otherwise this filter is pretty clean.

 

Looks ok. Sorry but I thought it was worth a shot. I have one at the shop right now that is pretty nasty. I will have to get some pic's of what I expected to see. I guess when it seems to neutral you will have to look to see what the solenoid data is doing. Maybe even put a pressure gauge on it but it appears as if the filter idea was a waste of time. Sorry

 

I had this happen..fixed it right up, car wouldn't shift right, thought I lost a couple gears

 

Hey, this was no problem whatsoever, was due for a fluid and filter change in 2 months anyway. I appreciate the help! I'm glad actually to find nothing that was noteworthy.

I'd like to see those pics of the nasty one if you get a chance to post them.

 

Yes it sounds like you may have some command issue I would as I said look at the data stream

 

Yes, thanks. I hear what you are saying about reading the datastream but it's just difficult, capturing it by yourself, knowing when to log and what to log etc..

Had another lock, unlock, lock episode today and again it was in the first 3-5 minutes of driving, this time at about 50 mph. This time it was just one rotation of lockup, unlock, then relock. Even though its in the first few minutes, since it's so hot outside, the trans oil temp and engine temp are hot enough that it's in the lock enable temp zone.

Now that it has happened twice, both times in the afternoon on the way home from work, I have a good idea when to log in autotap to try to get some good info. But I'm not sure what to log. I have an older version so the more parameters I set for logging, the less the frequency is, and the less likely it is that I'll catch the thing I need to see. So, what would be relevant to see in the log?

If I select everything under trans...it looks like this...

Del Trq Eng - Tran Input
Adaptable Shift
Trans Oil Temp
Trans input speed
trans output speed
TCC PWM Duty Cycle
32 DS Solenoid PWM
Trans Force Moter PWM
TCC Slip speed
Current Gear
Trans Force Motor Pres
Shift delay
Gear Box
Trans Tem
TCC apply time
Speed ratio

What is necessary out of that list...

If I add TPS
Engine speed
Maf airflow (?)

What else do I need to log?

 

Is there any chance that there's some kind of air bubble in the fluid stream that's causing this or no? I'm half tempted to disconnect the B&M trans cooler and reconnect to just the radiator cooler to see if that helps. I have had that cooler on the whole time without problem, dating back to the original install of the converter 7 years ago. I changed the rubber lines 4 years ago just as preventitive type maintenance. It's hot as hell out right now so I don't want to disconnect it if there's no chance that's the problem.

 

Read your DTC's. Are there any pending codes? Some errors need more than one occurance to trip the SES light.

FWIW, I'll disagree with Gilberts's advice on locking. locking in third gear should not be an issue and ther's no reason why you can't lock at speeds lower than 55 mph. It makes driving a high stall much more tolerable. I would lock in third and raised my 3-4 upshift to keep the car from being a dog in town.

I do concur with the advice of letting the car unlock when you get into the throttle, although I used a bit higher threshold %.