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"factory freak"...
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8,601 Posts
Discussion Starter #1
In a recent thread i mentioned in a recent thread that I was planning to do a TCC PWM solenoid mod to eliminate the PWM function.
Basically all I did was pull the PWM solenoid, remove the outer O-ring, then use a Dremel
Tool to cut a small groove across the end of the solenoid to allow fluid transfer from one
side of the fluid circuit to the other. Its basically the same as the solenoid being "on" all
the time, bypassing pressure regulating ability of the solenoid.




You can see the slot I cut across the the outer three ridges to allow AFL oil to bypass the solenoid valve,
and act on the TCC isolator valve.

As long as you don't cut into the land the O-ring sits in, this mod is reversible by simply re-installing the O-ring.
 

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"factory freak"...
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8,601 Posts
Discussion Starter #2
I have test driven my truck with this mod and it works great.
The lockup now functions with the lockup engaging 100% at about 42 mph.
It unlocks on deceleration, re-locks 100% after you get back on the throttle,
and unlocks under heavy throttle, just like an 80's-early 90's model GM would.

I also installed a Sonnax pinless 1-2 accumulator piston and pinless forward
accumulator piston.
The 1-2 piston was easy, but the forward piston was a bit of a chore with the 4wd
tranny crossmember in close proximity, but with a bit of enginuity it can be done
with the crossmember still in place.
And of course, a new filter and Type F fluid...
My pan hasn't been off for over 20K miles, and the Inside of the pan was spotless.
So clean I didn't even bother wiping it down...
 

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"factory freak"...
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8,601 Posts
Discussion Starter #3
I should also point out that this mod isn't really intended to cure a
P01870 code and/or vave body wear, but just to get rid of the PWM function
In a tranny that's not having problems with this yet, and possibly prevent
these issues from eventually occuring.
 

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the youngest has been
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4,358 Posts
So this just allows the TC to lock up on acceleration pretty much? I may try this. seems simple enough.
no it makes lockup more of an ON/OFF style like the older trucks ran.

the newer trucks run PWM (pulse width modulation) to slip the convertor into lockup. the lockup is so quick and crisp it can be mistaken for another gear change.

you can do something similar with just a tune.
 

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"factory freak"...
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8,601 Posts
Discussion Starter #6
The lockup still works as usual, following the PCM's programming table for the main TCC solenoid
Engagement and release points, just without the PWM slip function.
 

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"factory freak"...
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8,601 Posts
Discussion Starter #7
no it makes lockup more of an ON/OFF style like the older trucks ran.

the newer trucks run PWM (pulse width modulation) to slip the convertor into lockup. the lockup is so quick and crisp it can be mistaken for another gear change.

you can do something similar with just a tune.
Right.
You can alter the PWM duty cycle in the tune to basically eliminate it.
I've even seen people rewire the PWM solenoid to a solid ground instead of
through the PCM controlling it, and using a resistor to fool the PCM, but I'm not
sure a solenoid designed for duty cycle use would be reliable long term with fulltime
current running through it.

I tested this some using a momentary switch to ground the PWM instead of the PCM
doing it. You have to use a resistor on the PWM circuit to prevent it from setting a circuit
fault code, and disabling the TCC system completely.

Now if you do the solenoid mod, all you have to do is just reconnect the solenoid electrical
connector to satisfy the PCM.

Now I'm experimenting with the 3-2 solenoid as well. I've connected my momentary switch
up to ground it on my command, again using a 30K ohm resistor to keep the PCM happy.

So far, I can't tell any difference in 3-2 downshifts with it on or off.
No wonder GM eliminated this solenoid from the 4L60E in 2009...
 

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I should also point out that this mod isn't really intended to cure a P01870 code and/or vave body wear, but just to get rid of the PWM function In a tranny that's not having problems with this yet, and possibly prevent these issues from eventually occuring.
For anyone considering this modification, you may wish to read the following article from MOTOR magazine June 2006, an industry tech mag for mechanics/ dealer shops. I suppose that whether or not there would be a problem, would depend upon the model and year of your own vehicle. Too bad the OP has not stated his own vehicle specs.

http://www.motor.com/article.asp?article_ID=1039

The article says:
Should anyone modify the PWM or ECCC strategy to function as an ON/OFF apply while using a converter with a damper plate designed for PWM or ECCC, a tail end bump on the apply of the clutch would be felt, possibly resulting in a customer complaint. In some cases, a code for Converter Clutch Stuck On may also occur as a result of this modification to ECCC strategy vehicles.
 

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"factory freak"...
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8,601 Posts
Discussion Starter #9
Modifying the PWM solenoid is adifferent approach than the usual
Stake the TCC isolator valve, or replace it with a Teckpac "fixed" position valve.

Bypassing the solenoid still allows AFL pressure to act on the isolator valve as
It normally would, just without being bled down by the PWM solenoid.
So it probably doesn't nail converter apply pressure to excessively high levels
like staking it does.

As for the "tail bump" from the soft clutch damper, I haven't noticed it being a problem
on my truck.
But I have bypassed my main TCC lockup solenoid to full manual control temporarilly,
to see how it reacts to full lockup at lower vehicle speeds. Applying it as low as early 2nd gear
Isn't bad, but applying it in 1st does create a rather annoying "tail end bump" on the shift to 2nd gear.
2-3 and 3-4 aren't objectionable, in fact, it feels pretty nice to me having it locked while driving around
town...
It can produce a 200-400 rpm drop when locked even under fairly light throttle.
And there could be noticeable fuel economy gains to be had by locking it when the torque converter
is in its least efficient rpm range.
As for the "converter stuck on" code, its normally only set if the PCM detects a voltage drop on the main
TCC solenoid ground circuit when its not being commanded on by the PCM.

The PCM is looking for batt. voltage on this circuit when its not being commanded on, and a voltage drop
when its commanded on...
Again, I used a 30K ohm resistor to satisfy the PCM's circuit voltage expectaions while I have it bypassed
to manual control.
And just about any resistance rating resistor will work, as long as the resistance is at least as high as the
solenoid in question. Say, 30 ohms minimum. Lower than the solenoids resistance, and there's a chance
of burning out the circuit driver in the PCM.
 

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"factory freak"...
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8,601 Posts
Discussion Starter #11
Well you can test it for yourself with temporary wiring alterations at the PCM.
That's what I did before I pulled the pan for more permanent mods.
Who knows, just wiring PWM for full time current might hold up long-term.

Having a few extra PCM wires/pins is handy for this, as it allows you to test
things without having to cut up your wiring, especially before you decide you
like the mod or not.
 

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"factory freak"...
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8,601 Posts
Discussion Starter #12
Another update.
Still driving with the 3-2 solenoid disabled. Still can't tell any difference.
Monitoring MPG with my Torqe app, I've been observing changes in fuel
economy from early torque converter clutch engagement, and it looks quite
promising.
At a steady 35-36 mph on a slight uphill grade, I've seen gains
Of 4 mpg in most cases, and level ground gains of 2-3 mpg at speeds as low
as 25 mph.
So it looks like early TCC engagement could deliver significant economy
improvements with in-town and lower speed back road driving.
 

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the youngest has been
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4,358 Posts
Another update.
Still driving with the 3-2 solenoid disabled. Still can't tell any difference.
Monitoring MPG with my Torqe app, I've been observing changes in fuel
economy from early torque converter clutch engagement, and it looks quite
promising.
At a steady 35-36 mph on a slight uphill grade, I've seen gains
Of 4 mpg in most cases, and level ground gains of 2-3 mpg at speeds as low
as 25 mph.
So it looks like early TCC engagement could deliver significant economy
improvements with in-town and lower speed back road driving.
Transmission tuning is where I see the most mpg gains when I do my tunes. I have played with early lockup and saw good results. I personally dont care for it in my truck.
 

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"factory freak"...
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8,601 Posts
Discussion Starter #17
Transmission tuning is where I see the most mpg gains when I do my tunes. I have played with early lockup and saw good results. I personally dont care for it in my truck.
The lockup "feel" is definetly a personal preference.
I kinda like it, others just don't.

Exhaust drone can be another issue experienced on some
vehicles in lockup. My truck doesn't have a problem with it,
but my 86 Corvette had a heavy drone in lockup that made
It quite unpleasant.
 

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"factory freak"...
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8,601 Posts
Discussion Starter #18
Can't say I'd notice the difference between a stock and built trans on a 2.2. Only reason I'd be interested is for consistent RPM and better MPG.
I'd say 2.2l trucks could see considerable economy gains too
considering their high stall speed coverters.
 

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Headbanger Boogie
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1,789 Posts
Can't say I'd notice the difference between a stock and built trans on a 2.2. Only reason I'd be interested is for consistent RPM and better MPG.
Have you ever even had a build one to even form this opinion? Because if you did have any you would know the difference. I guarantee it would beat a 5 speed s10 easily with the same mods and that's even with a stock converter.



The lockup "feel" is definetly a personal preference.
I kinda like it, others just don't.

I love having full lock up. Maybe I should give this a try.
 

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"factory freak"...
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8,601 Posts
Discussion Starter #20
Like I said, all you have to is pull the PWM and TCC wires at the PCM
then connect them to a grounded momentary switch for testing, then
connect a couple resistors between a swtched battery source and the
terminals in the PCM to fool it into thinking those solenoids are still
connected to it to see if you like it or not.
 
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