TCC lockup and unlock between 45-55MPH

[horsepowerguru427]

As the title says i seem to be having a torque converter lockup and unlock continuously between 45-55 mph but only at cruising (roughly 20% TPS) After reading about TCC PWM and some other people that have the same issues with stall converters i increased the values to 100% max and 70%min as was reccomended to me. It did stop the problem, however now the truck feels mosre sluggish than before. Id like a better or more accurate way than this to fix the problem. the PWM increases was a giant leap from factory and doesnt seem right to me. Not new to vehicles or engine building, but have only been tuning for a couple years and would like some input.

2005 GMC yukon AWD 5.3 LM7
CAI, LT headers, no cats, 3" y pipe to single 3" cat back with delta 50 muff
209/217 .550/.550 LSA 12+1
2500 Stall Converter
4l65E


It runs well but the speed limit in my area is 50-55mph so this puts me right in the area im having problems while driving almost anywhere. Log file is from tonight, yes i know i have a lot of channels and things on there lol Also im posting a screenshot with timing circled as to show what area in the log I am referring to. I Have adjusted timing, VE, MAF, and everything else i can think of to fix the problem but nothing changes it other than TCC PWM.

Long time reader, first time poster....dont chew me up lol

[HATEHPTUNERS]

I'm not sure I understand what the problem is... But.. I'll ignore whatever your vague question is and just move on to what I'm seeing in the log... It shows in your log that your TCC is applying as early as 15MPH. You have not included your tune so we can't see what the lock up tables show... Why is it trying to lock up at 15? Post up your tune... Let's look at it from there.

[Tunercharged]

I have a bunch of transmission coolers running on mine to keep heat down, it’s hot in Florida. I turned off TCC lockup for all gears. Maybe lost 1 mpg, maybe not that much. Unless I will set it up just for highway cruising, I won’t set it up to turn on at all, IMHO.

[SiriusC1024]

I have a bunch of transmission coolers running on mine to keep heat down, it’s hot in Florida. I turned off TCC lockup for all gears. Maybe lost 1 mpg, maybe not that much. Unless I will set it up just for highway cruising, I won’t set it up to turn on at all, IMHO.

Wouldn't that make more heat due to the losses caused by the slip between the rotor and stator of the torque converter? That's where your 1 mpg is going. It's being wasted as heat.

[Alvin]

Post the tune file.

Also there is a brake fuse that can cause them to unlock anytime your not on the gas.

[horsepowerguru427]

sorry guys i thought i had the tune included. my bad!

[horsepowerguru427]

The main problem is I can Feel it trying to lock and then unlock over and over until I get above that speed or TPS. It also causes an RPM surge while this is happening. RPMs only go up and down by about 300-400 but Id rather find a good solution to this problem instead of throwing all this lockup at it which doesnt seem right.Thanks in advance.

[horsepowerguru427]

Alvin, It only does this under light throttle. It does not do it when off the accelerator or TPS past 20%

[Tunercharged]

Wouldn't that make more heat due to the losses caused by the slip between the rotor and stator of the torque converter? That's where your 1 mpg is going. It's being wasted as heat.

Yeah, basically it is just like a regular old torque converter with it programmed that way. I like it.

[Alvin]

sorry guys i thought i had the tune included. my bad!

Your lockup and unlock speeds are too close together. (2mph)

[horsepowerguru427]

Your lockup and unlock speeds are too close together. (2mph)

OH! well i feel super smart now. Didnt adjust it from factory. Thank you for taking a look and the advice!

[HATEHPTUNERS]

I have a bunch of transmission coolers running on mine to keep heat down, it’s hot in Florida. I turned off TCC lockup for all gears. Maybe lost 1 mpg, maybe not that much. Unless I will set it up just for highway cruising, I won’t set it up to turn on at all, IMHO.

You must NOT run your GM 4L60E or 4L80E transmission this way! You are going to melt the unit from the inside out.. What you DON'T know here is what is going to destroy your transmission. When a torque converter is commanded to lock up not only does the converter clutch internally apply, but a much larger percentage of fluid is then allowed to flow through the cooling system thereby controlling internal transmission temperatures. When you do not allow it to go into lock up you are essentially just recycling the hot fluid inside the unit. Think about a thermostat that sticks closed... Your motors going to over-heat. Now, think about a thermostat that has had multiple small holes drilled around it's perimeter so that even if it sticks closed you will get some fluid moving to the radiator.. That is what you are doing when you do not allow it to lock up! Yes, it will be moving some fluid, but NO it will not be moving enough to keep the trans temps under control. Those with trans fluid temperature gauges can verify that if you drive for 20+ minutes on the freeway in over-drive, with TCC lock up turned off, your transmission temperatures will SOAR.. There is a time and place for lock up and 90% of most vehicles need it to work as engineered. Racers-not so much. This is a BIG issue we end having to resolve on LS swapped vehicles. Many people don't know that older GM vehicles, and non GM vehicles, do not have a 12V+ wire coming off the brake pedal switch that must run to the PCM to allow lock up. When that wire is not put in place, or otherwise 12V+ provided to that one wire on the PCM the trans then over-heats and melts and the owner has no clue why. Most guys that come to my shop with smoked trannies in an LS swapped vehicle are because of this simple mistake. If you don't drive on the freeway-it's not that big a deal.. But if you are in over-drive, on the freeway, you absolutely must have it enabled, or make the necessary internal modifications to the transmission so that it can get the extra trans fluid capacity to the cooler that it needs to keep from melting.

[Tunercharged]

You must NOT run your GM transmission this way! You are going to melt the unit from the inside out.. What you DON'T know here is what is going to destroy your transmission. When a torque converter is commanded to lock up not only does the converter clutch internally apply, but a much larger percentage of fluid is then allowed to flow through the cooling system thereby controlling internal transmission temperatures. When you do not allow it to go into lock up you are essentially just recycling the hot fluid inside the unit. Think about a thermostat that sticks closed... Your motors going to over-heat. Now, think about a thermostat that has had multiple small holes drilled around it's perimeter so that even if it sticks closed you will get some fluid moving to the radiator.. That is what you are doing when you do not allow it to lock up! Yes, it will be moving some fluid, but NO it will not be moving enough to keep the trans temps under control. Those with trans fluid temperature gauges can verify that if you drive for 20+ minutes on the freeway in over-drive, with TCC lock up turned off, your transmission temperatures will SOAR.. There is a time and place for lock up and 90% of most vehicles need it to work as engineered. Racers-not so much. This is a BIG issue we end having to resolve on LS swapped vehicles. Many people don't know that older GM vehicles, and non GM vehicles, do not have a 12V+ wire coming off the brake pedal switch that must run to the PCM to allow lock up. When that wire is not put in place, or otherwise 12V+ provided to that one wire on the PCM the trans then over-heats and melts and the owner has no clue why. Most guys that come to my shop with smoked trannies in an LS swapped vehicle are because of this simple mistake. If you don't drive on the freeway-it's not that big a deal.. But if you are in over-drive, on the freeway, you absolutely must have it enabled, or make the necessary internal modifications to the transmission so that it can get the extra trans fluid capacity to the cooler that it needs to keep from melting.

That’s a lot of information I am not sure how to digest. I didn’t realize that that TCC in disengaged position would block the circulation of tranny fluid through the transmission coolers and actually I have not experienced this in practice. The diagrams of the 6L90 trans body fluid flow do not show any difference in flow to cooler circuit locked or unlocked as far as I can tell. I maintain a 150 rpm slip on converter at highway speeds pulling a trailer and have tranny temperatures of around 180 degrees max if it is a 105 degree day. Been driving like this for about 23k miles and it’s been working well. I’m using Amsoil in the tranny. This is the stock converter I’m using now, plans for higher stall converter later when time allows.I don’t know, is there something I can check to make sure I’m not creating a destructive situation?

[HATEHPTUNERS]

I was specifically referencing the 4 speed units-both 4L60E, and 4L80E. I've never experienced this problem with 6 speeds before. About the only thing we change on the 6 speeds in regards to TCC lock-up is to delay them so that they do not lock up on the 1-2 shift as they do with the factory programming. Never had one that did not lock up, nor over-heat from not locking up. We DO remove/replace the thermostatic valve on those so equipped so that there is constant full time fluid flow to the external cooler(s) and therefor delete the valve entirely and replace with a valve that we machine in-house.

I edited my post above for clarity.