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Discussion Starter · #1 ·
I want to understand how our GM ECM works to provide torque limiting. On my '04 I5 5-speed RWD I assume that the computer uses the ABS transmission speed sensor output compared against throttle pedal position and then provides a "safe" throttle position result to the throttle body. This must be to limit the load on the clutch, trans, & rear end.
One really great example of this was pulling my 1,500 lb. boat & trailer out of Saddlebag Lake. This is a pretty steep unpaved boat ramp at 10,068 FT elevation. After stalling the engine several times I ended up just holding the engine at 4-5,000 rpm and slipping the clutch all the way up the ramp. I doubt that it was actually making more than 50 or 60 HP & actually spinning a tire was impossible. Even at this altitude the engine should make at least 160 HP.
Another example is Sonora Pass on HWY 108 where traffic, tight turns, steep climb, and 9,600 FT. altitude have me in 1st gear at full throttle going 10-15 MPH and praying I don't have to stop for any reason. I know that plenty of power is available but the computer won't give it to me. At similar altitude but at higher vehicle speeds and in 3rd or 4th gear it seems to make really great power but get slowed down and in 1st or 2nd gear everything changes.
So next week and prior to the April 30th trout season opener my throttle body and ECM are going to James at Supermodulation for porting & tuning. I may still end up in 1st gear but I hope that there will be no more need for full throttle! I will post a result by mid-may. Does anyone know for sure how the system works?
 

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I think we're talking about traction control?
In that case you're pretty much right. The ABS detects wheel slip, tells the PCM, and the PCM in turn cuts the throttle.

It kinda sounds like something else might be wrong though. What happens if you turn TC off?
 

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Discussion Starter · #3 ·
With my Traction Control on the truck will not make enough power to move so it is never used. When new the dealer said they all worked like that. Because these trucks have no throttle cable there is no direct connection between your foot & the throttle plate. Any driver command to adjust the throttle position is processed by the PCM and as a result it is a program that is in actual control. Say GM decided that 100HP or half of the throttle plate opening was all that a manual trans truck would ever need in first gear, then that's what you would get. I'm sure these trucks never actually get to WOT in 1st gear with a stock tune & TB.
My question is what are the actual parameters that control throttle position plus cam and ignition timing. What the driver wants is not really what he gets. I'm hoping that this weeks Supermodulation modifications to the Throttle Body and PCM will put me in more direct control.
Big brother is alive, well, & thriving inside our vehicles.
 

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Alright, this is not gospel per say, but only what I've learned, researched and read about the TC Control, so take it for what you will, hopefully it helps you understand it as I have.

Torque limiting/traction control is important for several aspects of the truck to maintain longevity and life of the drive train and to some degree, even your tires and even during inclimate weather conditions:

1. It limits the amount of power/torque to the drivetrain in certain situations, whereas in the case as with a manual transmission, it allows full torque available to the engine and RPM control over the drivetrain at all times. With a "jackrabbit" start from idle, this can be quite a shock to the transmission with a powerful engine and cause premature wear if done consistently and often.

2. As it's name implies, with limiting the drivetrain's power at idle/stop, this allows for more traction, less tire spin and more "hook" when starting out, also prolonging the life of the tires. The loss of rear-end control due to high RPMs/tire spin, to the point of "peeling out tires" will happen without this.

3. On slippery or iced over roads, the TC control in conjunction with the brake system can help maintain control of a vehicle in certain situations to prevent sliding or total loss of control.

Bottom line is this, traction control is useful and great if you want a reliable, safe, commuting vehicle as it will save on wear and tear on your vehicle in the long run. However, if you want the full performance and power available of your vehicle, you'll want to turn the TC off or simply have someone like Supermodulation have it programmed out of your PCM. Regardless, if you do so while still under warranty, it could also void it, so do take that into consideration as well.

Hope this helps, good luck!

Big brother is alive, well, & thriving inside our vehicles.
Actually, it's more like GM is trying to cover it's "assets" and improve it's safety ratings from sue happy lawyers, sadly such is things these days...
 

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With my Traction Control on the truck will not make enough power to move so it is never used. When new the dealer said they all worked like that. Because these trucks have no throttle cable there is no direct connection between your foot & the throttle plate. Any driver command to adjust the throttle position is processed by the PCM and as a result it is a program that is in actual control. Say GM decided that 100HP or half of the throttle plate opening was all that a manual trans truck would ever need in first gear, then that's what you would get. I'm sure these trucks never actually get to WOT in 1st gear with a stock tune & TB.
My question is what are the actual parameters that control throttle position plus cam and ignition timing. What the driver wants is not really what he gets. I'm hoping that this weeks Supermodulation modifications to the Throttle Body and PCM will put me in more direct control.
Big brother is alive, well, & thriving inside our vehicles.
To the bolded...all of them :)
You're concerned with the ETC limits table, I think, which limits throttle according to RPM and requested torque. By design you should get WOT about 1-2 seconds after you ask for it. However, there is a big jump in available throttle over 200 requested lb-ft (30% vs 100%).
Is it possible you have a floor mat or something else which is impeding you from fully matting the throttle?
In any case, a tune will fix that issue.
 

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Discussion Starter · #6 ·
Don't confuse Traction Control and Torque Limiting because they have very different functions. When the Traction Control is turned on the PCM is directed to detect and minimize drive wheel slippage to assist the driver in maintaining control. This would be an active control function that seeks to match output power to the actual amount of available traction. The Torque Limiting function is different because its function is simply to reduce peak torque loading on the drive line. Although I have no idea how much Torque Limiting GM has programmed into these vehicles, I suspect that the highest level of Torque Limiting is with a manual transmission in 1st or reverse and only at low speeds. I also doubt there is any Torque Limiting at all in 3rd, 4th, or 5 gear. I also suspect that there may even be programming differences between 2wd, 4wd, manual trans, and automatics.
I repeat again, these are my assumptions and I am seeking detail on what GM has given us. The Truth is out there! Somewhere.
 

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Don't confuse Traction Control and Torque Limiting because they have very different functions. When the Traction Control is turned on the PCM is directed to detect and minimize drive wheel slippage to assist the driver in maintaining control. This would be an active control function that seeks to match output power to the actual amount of available traction. The Torque Limiting function is different because its function is simply to reduce peak torque loading on the drive line. Although I have no idea how much Torque Limiting GM has programmed into these vehicles, I suspect that the highest level of Torque Limiting is with a manual transmission in 1st or reverse and only at low speeds. I also doubt there is any Torque Limiting at all in 3rd, 4th, or 5 gear. I also suspect that there may even be programming differences between 2wd, 4wd, manual trans, and automatics.
I repeat again, these are my assumptions and I am seeking detail on what GM has given us. The Truth is out there! Somewhere.
Fair enough, but I think torque limiting doesn't really exist to the extent of your problem.
There is torque limiting setup in the calibration, but it's effectively disabled (set at 6000 lb-ft, yes thousand).

There is also torque management that reduces torque during a shift, but -obviously- you don't have that.

There is no programmed difference between 2wd and 4wd.

The above is what I've seen while tuning with HPTuners, which is not to say that I'm not missing something.
 

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Discussion Starter · #8 ·
Well my PCM & TB came back from James @ Supermodulation yesterday afternoon & was promptly installed. The startup was quick, painless (no codes), and it has only gotten better each of the 70 miles driven. Any hint of torque limiting is gone and both 1st & 2nd gears respond totally different than before. By the time I got home from work today I even found myself just not using 1st gear at all. That might not work with an I-4 but now in my I-5 5-spd 2wd 3.42:1 with a full tank, chubby driver, & 200# of stuff behind the seats 1st gear will only be needed when towing, loaded heavy, or starting on a steep grade. It has now become a granny gear.
I cannot be sure how much of the huge improvement is attributable to deleting the torque limiting, the 89 octane reprogramming, or the ported throttle body but the combined result is similar to when I converted my old '81 Suburban from a 350 to a 463.
It was lightly raining on my way home today & I was driving in my "Easy Rider Commute Mode" but on a tight 270 degree steep uphill turn in 2nd at about 2,000 I ended up dirt tracking the second half of the turn. I was really surprised it would do that at so little throttle. I have a G80 and it was totally controllable but next month I will need to order from Tire Rack again. Its always something but then I haven't made a payment in 8 years & the truck is now way more useful than when new.
I never did learn the details about how the GM torque limiting concept works but can say it will not be missed on this truck.
 

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It limits the fuel and timing on the 1st to 2nd shift, so you don't break parts
 

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Discussion Starter · #10 ·
Well I now have made three fishing trips up into the Sierras towing the boat to altitudes near 7,000'. Soon the higher 10,000' passes will be cleared & open for a true test but the preliminary result is great. The Supermodulation tune (including torque limiting removal) & throttle body mods plus the valve job have totally changed everything. Throttle response, power, and even engine breaking are all greatly improved. Power is at least equal to most 5.7L 1/2T pick-ups I have ever driven.
One guy in a new $60K Ford 1/2T EcoBoost with two Kayaks in back was really unhappy when I got tired of waiting and just blew by in my '04 Canyon towing a 16 1/2' boat up a grade at about 5,000'. When we finally reached the boat ramp after about another 15 miles all you could smell was Ford brakes from his effort to keep up. That was last week but it still makes me laugh. :wavey:
 
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