what can cause a converter to periodically unlock while cruising

[BOTTLEDZ28]

I have a 98 Tahoe with a 4L60E with 177K on it. Every once in a while, the converter will just unlock while cruising. It will go back into lock up eventually but its been happening everyday now. It used to only do it when it was raining out but not every time it rained. I thought I fixed it with a plug and wire change but it came back. Its not the brake switch.

 

[RDF1]

It could be a missfire causing it, but usually the MIL will flash at you. Atleast i think it does on the older trucks. i know the 99+ GMT800s do.
If you have ruled out the brake switch, id think it could be a solenoid acting up or a connection issue?

 

[RichLo]

The TCC solenoid unlock will unlock under fairly light load to save it from damage. Going up a hill will make it unlock or going into a heavy headwind.

 

[RDF1]

Do you have a way to scan the live data?
Wonder if it could be a bad TPS?

It should only unlock if the TPS/MPH/Gear algorithm is met or the Brake pedal is depressed.

 

[BOTTLEDZ28]

Do you have a way to scan the live data?
Wonder if it could be a bad TPS?

It should only unlock if the TPS/MPH/Gear algorithm is met or the Brake pedal is depressed.

I have had the truck scanned and have ruled out a faulty TPS. I have also ruled out the brake switch.

I can take off from a dead stop and steadily cruise up to about 55mph an count the upshifts. The can then feel the converter lock while watching the tach drop a few hundred RPMs. About 3-5 seconds later, the converter will unlock and stay like that for a while. It does go back into lockup at some point down the road and seems to stay there for the duration of my 10 mile trip to work and back.

I have watched the trans temp and it does not get hot to a concerning degree.

This has been doing this for a couple years now but it only used to do it when it was raining out. I figured maybe there was water getting into the trans connector or possibly even the taillight harness and triggering the brake light but I ruled that out. Someone suggested that it may be a misfire. I only pick up about 8 misfire counts on cylinder 3 over a 30 mile trip. That, to me, is normal considering the truck has 177K on it.

I can only think of it being something in the pan like the solenoid. I just didnt want to drop the pan and throw parts at it without getting some feedback here first.

 

[BOTTLEDZ28]

Not sure if this is of any help but the truck does have a 0411 PCM in it. It had a mail order Lextech tune in it which I recently discovered was a terrible tune for my particular application. I have 33" tires and 4.56 gears and the shifting part of the tune was terrible. I have been slowly making it better with a friend of mine tuning on the laptop but this converter issue has me stumped. I do not remember if it did it prior to swapping PCMs and I really do not want to put the black box back in just to see if it still unlocks.

 

[RDF1]

What is he tuning it with?

Sent from my SAMSUNG-SM-G870A using Tapatalk

 

[RDF1]

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Here is something ive been using for years. It is awesome to say the least!!

Put all your info in and the trans shifts like magic and the TCC lock and unlock is perfect.

http://home.windstream.net/philliphsmith/BC_Trans.zip


Its setup for HPT but transpose for EFI Live.

 

[BOTTLEDZ28]

im using efi live

 

[Supercharged111]

Sounds like a misfire to me, my truck does it too. After it unlocks, it needs to see the misfire count stay under a certain threshold for a certain amount of time before it decides it will lock the TCC again. Drives me nuts. Always happens at light load cruise, moderate load it won't do it. It will also misfire at WOT in 2nd and flash the MIL, but no MIL for the light load misfire.