Truck Converter Issue: Locks & Unlocks while cruising

[RWTD]

I have a customer with an '05 Avalanche with a built 427 that we're having issues with the converter locking/unlocking while cruising. (To get this out of the way, the misfire test is completely disabled.) It's an upgraded trans and stall from Art Carr. I need to give some specifics on the trans first: Art Carr set the K-factor to 140k (he said stock is approx. 110k). He also blocked the PWM (pulse width modulation), so to keep it from destroying the converter.

In fact, this isn't the only truck that I have experienced this issue with. I had another customer with an '02 truck with just a converter upgrade (stock trans), and his did the *exact* same thing. I sent an email to HPT about it back then (about 2.5 years ago). Here are their responses below:

Ken's response (seems like the answer):

Its a TCC test from the VCM. It's looking for what pressure the TCC slips at and we don't recommend trying to get rid of it.
It only happens during the 4th shift under very light throttle.


Regards,
Ken Cannata
HP Tuners LLC
[email protected]

-----Original Message-----
From: RWTD
Sent: Monday, August 28, 2006 12:33 AM
To: Ken
Subject: Torque Converter Question


Ken and/or Keith,

Do you have any idea what may cause an aftermarket converter to *slightly* lock/unlock when at cruising speed (I believe it's a Yank 3000)? It's on on/off on/off on/off sensation that is perceptible, tho not much. The rpms may raise/lower by just 100, if even if that. It's a continuous situation that happens between 45 and 55 mph on an '02 Silverado, but once over say about 55 mph it doesn't do it anymore. The TCC controls are factory, save for a change in tire size that resulted in the values being raised slightly for lock/unlock. I've even tried various lock/unlock settings, but have only managed to either lower or raise when this is happening.

Keith's response was:

TCC duty cycle.

Keith Prociuk
HP Tuners LLC
www.hptuners.com

I logged it, and so did the guy's local dealer with their Tech2, and the logs show that the pcm is commanding it to lock and unlock. I set the duty cycle to 100% (Max) and 90% (Min), and it didn't change a thing.

So, my question is, who else has experienced this, and did you find a fix for it? I don't understand why the "test", that Ken stated is the culprit, just can't be disabled?

Thanks for your help in advance. My customer is patient, but I feel bad for him that this is happening, and I want to get it rectified for him.

Sincerely,

James

[Bill@HPTuners]

My only experience with converter lock/unlock was due to the pcm thinking my vehicle was misfiring due to a large cam, I desensitized the misfire tables slightly and all was well from there on.

Something to look at.

[RWTD]

Thanks for your input, Bill. Misfire test is completely disabled, however.

[bartender_77]

Maybe I'm wrong but i always remember that, you never need to turn the misfire test completely off and what needs to be done is, change the misfire detection tables under the diagnostics-misfire tables, the revolution one and cylinder mode one and to higher numbers in the the lower and idle rpm areas so that pcm doesn't look for misfires at lower/cruising rpms, i had issues with cars not locking up after disabling the misfire tables, specially the P0300 code and after raising this numbers in the misfire tables that cured my problems, but maybe I'm wrong, just a thought!

[jimmyblue]

If this is the TCC slip-learning, dithering in and out,
maybe you need to kill the allowed-slip stuff. Is the
TCC_Mode bumping in and out of "Locked" to "--3--"
or is it just a soft flare? Is TCC PWM duty deviating
below (or to) your min limit? Maybe the locked-TCC
line adder or force motor needs bumped to accommodate
the greater motor torque at light load. Do you have the
General Pressure tab populated, on this vehicle?

[Chris@HPTuners]

if he blocked the TCC PWM does it just lock the converter by the enable solenoid? ie. apply full pressure when the enable solenoid is energized?

you should be able to log the TCC enable solenoid status in the scanner. You will also be able to see it if the TCC Mode is changing to Off at any stage.

Also, with converters they will unlock if TPS gets close to 0 so the vehicle brakes will operate effectively. I've seen this kind of race condition before with high stall converters (eg. on my own car):

1. cruising with TCC unlocked
2. TCC locks causing vehicle speed increase, throttle decreases
3. TCC unlocks due to throttle close, vehicle speed drops becuase converter unlocked, so throttle increases
4. throttle open now so TCC locks again, causing vehicle speed increase, throttle dereases, TCC unlocks again etc...

only way i could fix it was to set the lockup speed high enough to avoid these closed throttle unlocks.

[RWTD]

i had issues with cars not locking up after disabling the misfire tables, specially the P0300 code and after raising this numbers in the misfire tables that cured my problems, but maybe I'm wrong, just a thought!

Actually, you're right, it's just a thought. Disabling the misfire test completely doesn't hamper TCC control. However, I do appreciate you chiming in, buddy.

If this is the TCC slip-learning, dithering in and out,
maybe you need to kill the allowed-slip stuff. Is the
TCC_Mode bumping in and out of "Locked" to "--3--"
or is it just a soft flare? Is TCC PWM duty deviating
below (or to) your min limit? Maybe the locked-TCC
line adder or force motor needs bumped to accommodate
the greater motor torque at light load. Do you have the
General Pressure tab populated, on this vehicle?

Jimmy, good questions. I'll log all this again soon. I do know that the dealer logged it with a Tech2 and it does show the TCC commanding lock/unlock.

As for the General Pressure tab, no, it isn't populated, unfortunately. I wonder if there are some settings in there that would help to rectify this.


Chris, thanks so much for your response. I will look into this more for you.

[CashDudeHomie]

I had the same thing on my 2000. It did not only happen at 0% throttle; it happened at light to mid throttle. It always happened from 40-55mph. I could not get it to go away so I set the lock up to 60mph. It happened with the stock converter and the Yank. Has anyone figured this out yet?

[pmj341]

I'm having the same problem with my 07 C6 A6, my converter 3600 Yank, locks and unlocks on command, thus creating high trans temps at cruise.
when commanded with VCM controls to lock the temps drop 15-20 degrees!!
PWM what to do??
thanks

[Rigo_eff1fitty]

Bringing it back from the dead. Having this issue how do desensitized the misfire detection

[DMDay]

Just tuned a 2010 Silverado has this issue in 6th cruise at 65, he thought it was a miss fire , I thought more of lock up coming unlocked. was going to set to 90-100 but it dosnt have that tab, lots more crap than my 4l60. I wasn't logging convertor lock up, any ideas what to log?

[Jason Austin]

Bringing it back from the dead. Having this issue how do desensitized the misfire detection

It's under Engine Diagnostics - Misfire tab. You can disable the misfire detection by maxing out all sub tabs for Revolution Mode, Cylinder Mode and SCD Mode. If you want to desensitize and not disable, try adding 10-20% to the following, Revolution Mode - Normal - add your % to the 1,600 RPM and higher tables.