Hey another question those of you with this trans. I find in 4th the torque clutch lock up or so I think, seems to lock & unlock. When it unlocks the engine rises about 200-300 rpms. With gas getting back in the $4/ gallon area I would like to find out how to keep it locked. Seems just the slightest input change from my foot and it disengages. Is this typical with swaps? PO says Sinister programed the engine and it has a Zzp filter and program.

When it is in 4th and locked the engine turns only 1500 rpms at 60. It sounds good at that rpm.

Thanks for your advice.

Steve W
NE Grand Rapids, MI

Ur issue is in the tune. I had this same issue right after my swap was done and also a few months back after swapping PCMs...

All PCMs that control 4T65-E's are set up to allow the torque converter clutch to slip some at all times while it is "locked up". It is not a solid lock-up with NO SLIP like earlier transmissions employed.

The torque converter clutch used with the 4T65-E transmission is designed to be slipped like this and the PCM is always going to try to force it to slip by a small amount no matter what. You DO NOT want to alter the programming to force a 100% lock / no slip condition in one of these transmissions. According to Dave at TripleEdgePerformance, a full-lock with no slip can strip the lining right off the clutch inside the torque converter because it was never designed to hold the amount of torque necessary to maintain a full lock.

It is perfectly normal to see some RPM rise / increased TCC slip if you gently lay into the throttle while the TCC is locked up. But the PCM should increase TCC pressure to bring the slip back down to a low level quickly. Now we are talking about small slip numbers here. Normally with light load, I think the slip is only supposed to be 20-40 rpms or so. With increased load, you may see higher numbers such as 200-300 slip RPM. But you shouldn't see anything much higher with the TCC "engaged". You can view these numbers with a good scan tool, it will be under transmission data called "TCC SLIP RPM".

I remember reading a GM tech article some time ago about this type of TCC lockup strategy. GM said their tests showed that allowing some amount of TCC slip at all times improved engine vibration isolation without hurting fuel economy. They also claimed that employing this type of TCC lockup strategy allowed the TCC to be activated at lower speeds to improve overall fuel economy.

-ryan

------------------
OVERKILL IS UNDERRATED

Custom GM OBD1 & OBD2 Tuning | Engine Conversions & more | www.gmtuners.com

quote Originally posted by Darth Fiero: All PCMs that control 4T65-E's are set up to allow the torque converter clutch to slip some at all times while it is "locked up". It is not a solid lock-up with NO SLIP like earlier transmissions employed. The torque converter clutch used with the 4T65-E transmission is designed to be slipped like this and the PCM is always going to try to force it to slip by a small amount no matter what. You DO NOT want to alter the programming to force a 100% lock / no slip condition in one of these transmissions. According to Dave at TripleEdgePerformance, a full-lock with no slip can strip the lining right off the clutch inside the torque converter because it was never designed to hold the amount of torque necessary to maintain a full lock. It is perfectly normal to see some RPM rise / increased TCC slip if you gently lay into the throttle while the TCC is locked up. But the PCM should increase TCC pressure to bring the slip back down to a low level quickly. Now we are talking about small slip numbers here. Normally with light load, I think the slip is only supposed to be 20-40 rpms or so. With increased load, you may see higher numbers such as 200-300 slip RPM. But you shouldn't see anything much higher with the TCC "engaged". You can view these numbers with a good scan tool, it will be under transmission data called "TCC SLIP RPM". I remember reading a GM tech article some time ago about this type of TCC lockup strategy. GM said their tests showed that allowing some amount of TCC slip at all times improved engine vibration isolation without hurting fuel economy. They also claimed that employing this type of TCC lockup strategy allowed the TCC to be activated at lower speeds to improve overall fuel economy. -ryan

Good stuff.

Thanks for the info.
With just the slightest and I mean slightest change in my foot pressure on the pedal it goes out of lock and stays out. It is hard to get it to lock up. Unfortunately the exhaust is very loud in this car and with the drop in engine rpms, the amount of the clutch lock up makes it a lot quieter.

I'm on my forth transmission rebuild. I'm still afraid to put the hammer down after breaking three input shafts, the last one a. $1000 aermet 100 alloy. The car is running now but it is now doing exactly the same as yours. Sounds like I have a bad tune on it. At least that sound a lot cheaper than the other ones. I'm not happy though after dropping more than $5000 on rebuilds and a performance built transmission I shouldn't be afraid to mash the loud pedal. I can only suspect bad parts or a bad torque management tune.

The TCC shouldn't unlock with the slightest pedal increase UNLESS you are already giving the engine moderate throttle. IE: Going from 10% to 15% throttle opening at 50mph shouldn't cause the TCC to unlock. But if you're already at 40% throttle and give it 50%, it may very well unlock.

The PCM may disengage the TCC if it detects excessive TCC slip RPM. What you may want to do is connect a scan tool and see what the TCC slip RPM is doing. There might be something else going on as well, so make sure the PCM isn't detecting another transmission component slipping.

Torque management is essential to keeping these transmissions alive. Some tuners like to disable or severaly dial back the torque management to inflate the "power gains" their tunes are able to find; but this can spell doom for the transmission, espcially if you are working with a high power application. As good as the 4T65-E HD transmission is, it has some design flaws in critical areas that severely hinders its power handling capability. Dave at TripleEdge has done extensive research into these limitations and found a critical one that has to do with the casting of the case in an area that affects drive sprocket chain alignment. There just does not appear to be enough room in the transmission to "fix" this problem; so I'm convinced using a different transmission (such as the 4T80-E) might be the only way to work around this.

No the trans comes out at just the slightest throttle change in letting up or de accelerating. Not accelerating. You programed the ecm for Jesse.

quote Originally posted by solotwo: No the trans comes out at just the slightest throttle change in letting up or de accelerating. Not accelerating. You programed the ecm for Jesse.

Do you have stock TC? Have you checked your fluid level?

Stock TC, ok just so we are talking about the same thing, what are you referring to? I dont know if it is stock. I would have to get a hold of PO. And he is busy so it is hard to get any info from him. Yes I checked the trans just after I got it and found it was down a quart. I found the leak and took care of that.

[This message has been edited by solotwo (edited 02-04-2013).]

Well good news. I made some adjustments and I managed last night going home to keep it in lock up or whatever. It maintained 1500-1600 RPMS well over 13 miles. So you want to know what did I adjust? I adjusted the "nut behind the wheel". I was tired last night and it was cold so I left my Merrell winter shoes on and drove home. Being tired I let my left leg lean up against the center console. Well it seems that angle is the angle needed to push the "gas pedal" and keep your foot steady. I tried it this morning and managed to go a long time in lock up. Interesting that something like that would make a difference.

quote Originally posted by solotwo: Stock TC, ok just so we are talking about the same thing, what are you referring to? I dont know if it is stock. I would have to get a hold of PO. And he is busy so it is hard to get any info from him. Yes I checked the trans just after I got it and found it was down a quart. I found the leak and took care of that.

Torque Converter.