converter will not lock under wot

[camcojb]

it definitely locks, and is fine at anything under 100% tp. But at wot if it down shifts it unlocks and will not lock again.

I can get it to work properly for 1-3 times if I reload a different tcm tune, or usually if I just reload the same tune. But it always goes back to not locking. If I get it locked, and then go wot at a speed that doesn't allow downshifting, then it will remain locked throughout the run. But if it's completely locked in say 5th gear at 50 mph or so and I go wot, it downshifts and will not re-lock at any speed.

I've tried everything I can think of. I've lowered the locking to super low mph's also, but no matter what, if it downshifts it's over. Like I said it will work fine a time or two or three after a flash, just long enough for me to think it's fixed, but then you jump in the truck the next time and no lock. Does it in normal and tow/haul.

Again, this is only at wot, no problems locking at lower tp%. I've reset taps and it's hit or miss as to whether it will work or not. This is on a high power tune with twins, SCIV and 1058 billet converter, LMM with 6 speed.

Final question since I know Mike L will ask, but is there any way to know if the tcc is being commanded in the EFI Live software? I saw a pid but it does not work as far as I can tell. I do not have access to a Tech II. I do not think there's any issues with the trans or converter, they work perfect except for this one glitch. It never fails to lock at normal or spirited driving. It's like once you get above a certain power level there's a table in the tcm that says "hell no, not going to lock it............. " I've heard this is an issue on high powered trucks, but as of yet I have not heard of anyone solving it.



Jody

[vortecfcar]

Jody,

I have a log file sitting in my email box from a customer with an issue I fear is similar to yours. I have a quick question for you just so that we're on the same page.

Have you tried raising your minimum TCC apply?

My thought is that the Alllison has a table that references TCC slip to PWM gain in order to figure out how much pressure it should apply to the converter clutch in order to get a clean, but not harsh lock. If you downshift under WOT you may put the TCC slip axis beyond the factory limits or into a new range where lockup is simply abandoned. My first plan of attack on this truck was going to be to raise minimum lockup pressure to see if we can get the converter to lock quickly before it goes into the dead zone. Second would be to see if there's a way we can aviod converter unlock on certain shifts altoghether.

I still have to look over the logs when I get to my other computer.

Nick

[camcojb]

Jody,

I have a log file sitting in my email box from a customer with an issue I fear is similar to yours. I have a few questions for you just so that we're on the same page.

Have you tried raising your minimum TCC apply?

My thought is that the Alllison has a table that references TCC slip to PWM gain in order to figure out how much pressure it should apply to the converter clutch in order to get a clean, but not harsh lock. If you downshift under WOT you may put the TCC slip axis beyond the factory limits or into a new range where lockup is simply abandoned. My first plan of attack on this truck was going to be to raise minimum lockup pressure to see if we can get the converter to lock quickly before it goes into the dead zone. Second would be to see if there's a way we can aviod converter unlock on certain shifts altoghether.

I still have to look over the logs when I get to my other computer.

Nick

no, raised the maximum which I thought helped, but after 3 wot datalogs it wasn't locking anymore.
What you're thinking would go exactly with what is happening. I'll give it a shot and see what happens. My stock tune was zeroed out on the minimum table everywhere.

The only way I've been able to keep it locked every time at wot is to not let it downshift, which is easy to do. However, that's certainly not an ideal trans tune on the street.

Thanks Nick, I'll post back.

Jody

[jpowel29]

Jody,

Have you tried raising your minimum TCC apply?

Nick

Nick,

I went into the TCC min apply/duty cycle table (which was factory set to zero) and increased it to 45% (and applied some smoothing to avoid knocking my teeth out on the steering wheel). I also went into the TCC max apply/duty cylce table (which was factory set to 65.62%) and increased these to 95%. The data logs only show max duty of 65.62% even after my changes. Max TCC Pressure apply solenoid commanded shows 152psi when max duty cycle is attained.

These changes helped TC Clutch lock up initially but as was posted earlier in this thread, it did not keep it from unlocking. Once it unlocks, it will not re-lock due to the clutch slippage rpms (my educated guess here but it looks to be the case in my data logs). From here the slippage continues, heats the trans fluid, and will eventually throw a P0741 DTC. Does this during normal street driving (up through all 6 gears) and also did the same thing on the dyno (locking out 4th gear). CoPilot does not seem to prevent TCC unlock (even in race mode/TH). Going to try a different CoPilot control box. Trans/converter will be coming out. Going to discuss symptoms/solutions with trans builder and converter manufacturer.

My converter has a mech diode (no stator). This may be adding to the excessive slippage rpms.

[IdahoRob]

Nick,

I went into the TCC min apply/duty cycle table (which was factory set to zero) and increased it to 45% (and applied some smoothing to avoid knocking my teeth out on the steering wheel). I also went into the TCC max apply/duty cylce table (which was factory set to 65.62%) and increased these to 95%. The data logs only show max duty of 65.62% even after my changes. Max TCC Pressure apply solenoid commanded shows 152psi when max duty cycle is attained.

These changes helped TC Clutch lock up initially but as was posted earlier in this thread, it did not keep it from unlocking. Once it unlocks, it will not re-lock due to the clutch slippage rpms (my educated guess here but it looks to be the case in my data logs). From here the slippage continues, heats the trans fluid, and will eventually throw a P0741 DTC. Does this during normal street driving (up through all 6 gears) and also did the same thing on the dyno (locking out 4th gear). CoPilot does not seem to prevent TCC unlock (even in race mode/TH). Going to try a different CoPilot control box. Trans/converter will be coming out. Going to discuss symptoms/solutions with trans builder and converter manufacturer.

My converter has a mech diode (no stator). This may be adding to the excessive slippage rpms.

I'm guessing you have converter issues with this example.

[rcr1978]

Nick,

I went into the TCC min apply/duty cycle table (which was factory set to zero) and increased it to 45% (and applied some smoothing to avoid knocking my teeth out on the steering wheel). I also went into the TCC max apply/duty cylce table (which was factory set to 65.62%) and increased these to 95%. The data logs only show max duty of 65.62% even after my changes. Max TCC Pressure apply solenoid commanded shows 152psi when max duty cycle is attained.

These changes helped TC Clutch lock up initially but as was posted earlier in this thread, it did not keep it from unlocking. Once it unlocks, it will not re-lock due to the clutch slippage rpms (my educated guess here but it looks to be the case in my data logs). From here the slippage continues, heats the trans fluid, and will eventually throw a P0741 DTC. Does this during normal street driving (up through all 6 gears) and also did the same thing on the dyno (locking out 4th gear). CoPilot does not seem to prevent TCC unlock (even in race mode/TH). Going to try a different CoPilot control box. Trans/converter will be coming out. Going to discuss symptoms/solutions with trans builder and converter manufacturer.

My converter has a mech diode (no stator). This may be adding to the excessive slippage rpms.

What pid did you use to log the duty cycle?

[jpowel29]

PID Caption - TCCDC
PID Description - Torque Converter Clutch Duty Cycle

I also log
TCCPCSCP - TCC Pressure Control Solenoid Commaned Pres
TCCSLIP - Transmission Converter Clutch Slip Speed
TP - Throttle Position
TFT - Fluid Temp
TIS/TOS - Trans input/output shaft speed
GEAR
Engine RPM

[jpowel29]

My converter has a mech diode (no stator). This may be adding to the excessive slippage rpms.[/QUOTE]

After re-reading this part of my post I wish to edit the part that makes no sense. My converter does have a stator...it is just missing the sprag. It is a spragless design (not a mech diode either) which I believe could be partially responsible for the excessive slippage and extra heat. It does not help me explain why the lock-up will suddenly dis-engage and then not re-engage however.

[camcojb]

My converter has a mech diode (no stator). This may be adding to the excessive slippage rpms.

After re-reading this part of my post I wish to edit the part that makes no sense. My converter does have a stator...it is just missing the sprag. It is a spragless design (not a mech diode either) which I believe could be partially responsible for the excessive slippage and extra heat. It does not help me explain why the lock-up will suddenly dis-engage and then not re-engage however.

once locked mine will only disengage if it downshifts. Again, goes back to the theory many have that we with the aftermarket looser converters and bigger power are making more slip than the trans wants to see so it won't command the converter to lock.

Solutions seem to be:
1. Find a table that controls the un-lock of the converter at downshift, and change it to not unlock. That would solve the rolling wot issues where the converter is locked and then you go wot to pass for example, it downshifts and unlocks and will not relock until you back off the throttle.

2. For the drags, we need to find out if there is a table that references slip in regards to locking the converter and see if it can be adjusted. It seems like once slip goes past a certain point it will not command lockup.

3. Get a tighter converter.

I have a good friend who is a trans calibrator for GM, and I've sent him an e-mail in regards to this. This may not even be a tuning issue in the trans, it may be a mechanical issue with the slippage that they cannot overcome. I'm interested in what he has to say, and will post back.

Out of curiosity, have any of you guys got your truck to lock in second or third gear on a dragstrip run? I think Rob mentioned his locks in 3rd. I've lowered the 2nd and 3rd gear lockup down to 18 mph, but mine won't lock until 4th on a boosted 4wd launch and run. At least it's locking again in 4th and 5th gear, but getting it to lock in 3rd and maybe 2nd would definitely pick up some et.

Jody

[jpowel29]

I have not logged the slippage before on the strip but I will be doing so from here on to keep up with it.

I will be re-installing my old converter and I will get some data logs on it to see how it behaves. It is a Georend and is likely comparable to a SC 1055.

I agree that there have to be some "hidden" tables/parameters that are over-riding the tuneable parameters we can see in the TCM. It is about the only plausible explanation for the unlocking we are seeing. I maxed out the TCC duty cycle tables and lowered the apply speeds (in 2nd & 3rd gears) that should have locked the converter and kept it locked (even down to zero throttle position at speeds above 25mph).

I will know if the cause is mechanical or hydraulic by next week (should have the trans/converter out this weekend).