My TC was doing that exact same thing after my Wheatley tune. It would lock/unlock constantly, it was driving me nuts and i knew it wasn't good for it.

He tried to fix it but couldn't. Nelson's tune fixed it right up.

moral of the story: it could be a tuning issue.

 

Got a tech II hooked up to it today and got a look at what it was doing. TPS, coolant temp, and trans fluid temp inputs were all good and stable. Misfire data was zero on all cylinders. After looking at the P1870 diagnostics the reason why its not setting that code is because its not slipping 150-800 rpms for more then seven seconds. I ran the TCC solenoid test which commands the TCC to engage with max duty cycle on the PWM solenoid and with the rpms held at 1000 rpms in gear with the brakes on it would kick in and kick out, in and out, and then finally it kicked in and locked and killed the engine like it ought to. I tried it multiple times and it did not kick right in and lock and kill the engine, it studdered. Going down the highway at 65 with it cycling like mad the TCC was always commanded on and the duty cycle was 95%. As far as the PCM was concerned the TCC was engaged and should have been staying engaged. The slip speed however would initially start out at 0 rpms and then as it started cycling it would toggle between 50 and 150 rpms and then randomly go back to 0 slip rpms. The only thing it could be is a bad torque converter, the synthetic fluid that is causing it to slip but I wouldn't think it would slip and then not slip like its doing, or its somehow loosing pressure between the TCC solenoid and the converter. I'm not sure if there is a test port for the TCC fluid pressure or not, I doubt it. Its looking like its a bad converter.

Edit: After sitting here thinking about it the converter clutch either works or it doesn't. I had one on an 05 thats designed to have a certain about of slip to make a super soft lockup and the commanded slip speed was say 30 rpms but it was bouncing between 0 and 100 rpms slip and it ended up taking a converter. Once it reached highway speed and went into full lockup it was fine but during the designed slip on initial lockup it it shuddered bad. I think I'll try a transgo SK kit and seperator plate and put some good old Dextron III in it first and see what happens.

 

It is fixed. Dropped the valve body and put a transgo HD2 shift kit in with the PWM eliminator valve. There was some scoring in the valve body bore too, nothing excessive but enough to cause problems. Works like a charm now. TCC lockup feels like a 5th gear shift, not that see the tach drop a little and not feel anything crap. GM says to replace the valve body or you can go this route. Transgo > GM

 

Mine did it bone stock and with a Yank 3000. The only fix I could find was to raise the lockup MPH to 55 and the unlock to 50. If my 8 year old never-rebuilt 4L60E ever goes, I'll check the valve body for damage.

 

I recently did a transgo hd2 on my 00' and now I think I'm having a similar problem. under very light load after it shifts into second its as if the converter is locked and then engine bods down unless I give it alot more throttle. I also did a motor swap and I'm waiting on a tune to see if it is a tuning issue. However, does this sound like something in the trans I could of goofed up on when installing the shift kit? sorry for the vague description thanks for any help,

Clint

 

mine is doing the exact same thing. it did it with the stock converter and now with the yank. if im going up a hill or acelerating it will lock but coasting or letting too much off the gas it unlocks. its driving me crazy and it also does it around town too!!!

 

It can be fixed in the tuning....

 

is this something I should tell wheatley about while he has my computer? I mean what do I tell him? I'm having a hard time putting my problem into words. is it simply the lockup speed being too low or what? thanks,

Clint

 

I'm having a problem too with my PI 3600 Stall at 15% throttle the converter tries to lock and I hear grinding sound and I'm trying to tune it for 2 weeks now and cant make it right. returned the stock setting now the rpm plays when I'm at wot It goes and stops goes again then stops its like something is holding it

 

I think maybe I just read your post on ls1truck? Since I'm working with a mail order tune I feel like I should try and tell wheatley what some solutions are for this problem, it sounds like its hit or miss with the tuning. what causes the lock up to happen so early?. Also do your trucks do it with more throttle as well or just easing into it? Mine seems to do fine wot but putting the trans in 2nd and mashing it from 30mph seems to yeaild the same "locked up" feeling.