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Torque convertor staying locked up causing stalling?

SnowDrift

SnowDrift

Ultra Conservative. ULTRA!
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Location
Central Ohio map dot
2005 Tahoe - 5.3 with +308,000 on the odometer

Two times in the past week or so, when slowing down to stop the engine acts as if wants to die. The first time it happened as I pulled up to a stop light in town and it just stalled. I put in park, started it up and drove away. I continued with the remainder of the trip which involved a couple errand stops over the course of about 90 minutes or so.

The second time it happened, I had just pulled off the road into a parking lot and idling up a hill, it acted as if it wanted to do it again, so I added a little throttle to the top of the hill, coasted down the other side to a parking spot and without a little throttle, I think it would have died out. Before it stalled, I put in neutral and it was fine. I put in reverse and backed up a bit and it was fine. I put into park and shut off with the key. A couple hours later, I started it up and made the 20 minute drive home without issue.

Ideas?
 
Your instincts sound plausible. Ya need a scanner that can read the call for lockup and see if the Komputer is calling for the tc lockup. There is other possibilities
But starting with the same device and watching what happens live is where it begins.

Smell that ATF.

308 on the ticker- that is due for a rebuild any day now.
 
Scanner will only tell you if it commanded lock up or not. if its sticking then you wont catch it unless you watch your TCC slip speed. start it up and watch the slip speed in drive with you foot on the brake. Then make sure its doing the same thing when you stop. If the slip rpms are really low when it wants to stall its a good indication is sticking on. You could also disable the TCC and see if the fixes the issue.
 
ATF smells like a landfill full of dirty diapers - perfect! Schaeffer's smells awful right out of the jug. I'll see if I can round up a scanner to borrow. Thanks for the tips, guys.

Is the disabling of the TCC something I can do through the scanner?
 
SnowDrift said:
ATF smells like a landfill full of dirty diapers - perfect! Schaeffer's smells awful right out of the jug. I'll see if I can round up a scanner to borrow. Thanks for the tips, guys.

Is the disabling of the TCC something I can do through the scanner?
Click to expand...

I believe most scanners will give you an option to disable the TCC
 
Had that happen on a fresh rebuilt 700R4.
Rebuilder mailed me over a new internal harness ans IIRC a switch.
About 20 below, outside, He mailed over a hundred dollar bill so got that changed out, reported back it was a success, he mailed over nuther hundred. 🤷‍♂️😹😹😹
 
Sounds like the EGR is sticking open. More throttle allows the engine to run with unexpected high EGR vs. run badly at idle.

You have done the pop the transmission into Neutral when it's acting up to help eliminate or confirm the sticking TCC theory. This "Unloads" the engine even if the TCC is working properly. So a badly running engine, due to any number of reasons, may run better unloaded.

A sticking TCC should be pushing you through the brakes when stopping. Is it? With space to stop add some throttle to see if it's pushing you when acting up. You should know what it does normally with some throttle aka power braking while rolling or a brakestand.
 
WarWagon said:
A sticking TCC should be pushing you through the brakes when stopping. Is it? With space to stop add some throttle to see if it's pushing you when acting up. You should know what it does normally with some throttle aka power braking while rolling or a brakestand.
Click to expand...
No. Applying the brakes stops the vehicle. Both times this happened was when I was coasting to a stop and was already nearly stopped - probably under 10 mph when I noticed the idle seemed a little low.
 
SnowDrift said:
No. Applying the brakes stops the vehicle.
Click to expand...
Normally without the engine "loading up" and making you stomp the brakes harder? If so I suggest you start with engine not running well.

Low fuel pressure and my favorite is a sticking EGR for a PIA to troubleshoot because to avoid warranty claims (and nuisance) with slow primitive ECM's there is a timer where the engine must stay running for any codes to trip. EGR stuck is a difficult code to set if it frees up and closes. Took me awhile on a 4.3L CA Emissions with an electronic EGR valve to find it as non-CA had vacuum valves. Had to order a valve off a 1994 to get the proper EGR valve in Colorado at the time. I pulled it off the engine as a WAG and found it was still hung up open at the time. A tap and it snapped shut.
 
WarWagon said:
Sounds like the EGR is sticking open. More throttle allows the engine to run with unexpected high EGR vs. run badly at idle.

You have done the pop the transmission into Neutral when it's acting up to help eliminate or confirm the sticking TCC theory. This "Unloads" the engine even if the TCC is working properly. So a badly running engine, due to any number of reasons, may run better unloaded.

A sticking TCC should be pushing you through the brakes when stopping. Is it? With space to stop add some throttle to see if it's pushing you when acting up. You should know what it does normally with some throttle aka power braking while rolling or a brakestand.
Click to expand...
It wont push though the brakes. I've have several sticking TCC over the years come into the shop. It will bog down the engine coming to a stop then stall. That causes the TCC to unlock and it will restart and drive with no issues until it goes into lock up again. A sticking EGR could be the case, but if it was stuck open it will cause a rough idle all the time and normally a position sensor code because it knows the position and if its not closed it sets a code. GM had a TON of TCC issues. We replace at least one or two 6l90/6l80s a month due to the TCC clutch coming apart and wiping out the transmission.
 
Best way I can describe a stuck TCC is that it's similar to trying to stop , while driving a stick , without pushing in the clutch .
 
Your torque converter cannot lock up in 1st unless there is a SERIOUS problem inside the transmission. GM learned after the 700r4 to make it so fluid pressure is not available to the tcc circuit in 1st gear. So unless you've completely lost say your stator bushing, I just don't see how your converter could be locked at super slow speeds. The last 4l60e I built lost the lockup solenoid and had it stick on, but even with that the truck never tried to stall out because in 1st it would unlock. Sounds to me like you're having other issues.
 
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