this is in a 99 s10 blazer 4.3 with 4l60e. from around 30 to 60 the conv. locks for about 5sec. then unlocks for about 3sec. but when over 60mph. it will stay lock up. changed tcc switch inside trans. did not help.. changed tps. did not help. no codes in computer. also checked brake light switch. NEED HELP!!!!

 

On the LSx motors this is a sign of random misfires. They
may be too sparse-occurring to qualify for setting a code
but can still bother the TCC. Is this a fresh problem, did it
follow some engine mods or new torque converter? See any
other drivability degradation (bucking, sputtering etc.)?

 

started right before motor spun rod bearing.. installed new motor cleared all codes after install. motor does ack like it stumbles alittle during aceleration.

 

think "jimmyblue " is correct

 

drove car with snap on scanner hooked up to watch if the computer was telling it to unlock but it showed that it was staying locked up. the only thing that would change is the duty cycle. at 60mph. the duty cycle was showing 57% but when you slow to 55mph. the cycle would drop to 21% and that is when it would start unlocking.

 

changed every thing plugs, wires, cap, rotor,tps,map sen,mass air. only thing not changed is coil and egr.

 

still need help!!!!!1

 

How many miles are on your transmission? I have seen the second gear check ball get stuck in the separator plate. When this happens it can make the trans shift hard and also do some weird stuff when the tcc is applied. You would have to drop the valve body to see if this is the case. But might be something to check. I did a repair similar on a friends 95 Z71 just after the warranty had expired at about 38K and now the truck has almost 190K. I did take the tcc regulator valves in the valve body and pin them with a inner pump slide spring from a 4l60. He thought he was going to have to buy a new trans and it was a very cheap fix. Might be something to consider. Vince

 

If it is not unlocking per se, but only flaring / slipping in the
TCC you might have worn it out, or might be supplying it too
little commanded main line (or, PWM just sucks and ought to
be gotten rid of, take your pick).

On my car 21%, 57% or 100% of not-enough-line was too
little for the small diameter converter clutch to work with.
I worked the line pressure up some but eventually got a
better converter.

Things that corrupt the airflow reading can starve the line
(PCM commands too little based on false-low load).

You might try cleaning the MAF if this vehicle has one, and
think about whether you have added mods which would make
it need tuning for airflow (any "breathing" power mod, basically).

 

I am still with JimmyBlue here

Has it happen for the first time back in 97 in a LT1 Vette we put a stall in The smaller size of the TC set off random missfires. Once we finally got a table to tune it was gone forever

 

but everything is bone stock