[DFW1LE]

Having read through this eLSD thread, it appears to me, that these issues are not exclusive to ZL1s. I am not a drag racer, nor ZL1 owner, but would expect the same from 1LEs. I am not even fully broken in yet, but do have a feeling the car could launch better from a stop with its M6.

[crazydmc]

Originally Posted by DFW1LE

Having read through this eLSD thread, it appears to me, that these issues are not exclusive to ZL1s. I am not a drag racer, nor ZL1 owner, but would expect the same from 1LEs. I am not even fully broken in yet, but do have a feeling the car could launch better from a stop with its M6.

I didn't read the entire thread but it seems everyone thinks eLSD should have something to do with managing wheel spin. the eLSD (electronic limited slip differential) is managing the slip % between the left and right rear tire only. if one wheel starts to spin over a certain % then the diff will lock more to get power to the other wheel. on a track this is probably a good feature. for launching or drag racing you should want 0% difference (100% locked) -- but this has nothing to do with whether or not you are lighting up your tires on launch or not.

obviously if you have traction control on, power is cut drastically when you are trying a fast launch... the traction control logic is great for keeping someone safe on the road, but will not get you the best launch possible... up to the driver with traction control off (with an M6)

[travislambert]

Originally Posted by crazydmc

I didn't read the entire thread but it seems everyone thinks eLSD should have something to do with managing wheel spin. the eLSD (electronic limited slip differential) is managing the slip % between the left and right rear tire only. if one wheel starts to spin over a certain % then the diff will lock more to get power to the other wheel. on a track this is probably a good feature. for launching or drag racing you should want 0% difference (100% locked) -- but this has nothing to do with whether or not you are lighting up your tires on launch or not.

obviously if you have traction control on, power is cut drastically when you are trying a fast launch... the traction control logic is great for keeping someone safe on the road, but will not get you the best launch possible... up to the driver with traction control off (with an M6)

I agree it's not an issue with the eLSD.

The thread is misnamed and jumps around a bit. Take a look at the attachment in post #97 to get up to speed.

[crazydmc]

Originally Posted by travislambert

I agree it's not an issue with the eLSD.

The thread is misnamed and jumps around a bit. Take a look at the attachment in post #97 to get up to speed.

thanks, interesting write up..... I agree the slip % calcs (resulting in bogus spikes) at such slow speed should probably be suppressed or managed better by the car... these spikes appear to be causing the driveablility issue.

[GarnetRedJuan]

Lines of code to fix this:

int speedBuffer = 5, timeBuffer = 15 ; // 5 mph , 15 secs arbitrary
if(wheelspeed <= speedBuffer || timeFromLaunch <= timeBuffer)
{
//do nothing
}
else
{
//execute logic
}

[travislambert]

Here's my logic.

(Of course, the 5 MPH and 15 MPH are arbitrary constants which may require testing to fine-tune.)

float tractionManagementFactor = 0.0;

if (ptmMode == RACE){
	// - This covers the dragstrip launch -
	// Give the driver the 650HP they paid for and wish them good luck
} else if (rearWheelSpeed <= 5 MPH) {
	// - This covers any speed calculation error and a little spin on gentle starts -
	// The rear wheels are barely moving, they'll survive ;-)
} else if (rearWheelSpeed <= 15 MPH) {
	// Phase in the traction management spark timing adjustment between 5 and 15 MPH
	tractionManagementFactor = (rearWheelSpeed - 5 MPH) / 10 MPH;
} else {
	// At 15 MPH of rear wheel speed and above, the car will behave exactly as it does today 
	tractionManagementFactor = 1.0;
}

...

[cwebster]

Originally Posted by travislambert

Do you guys ever watch the wheel slip percentage on the eLSD display?

I have the manual transmission, which I've always felt like it's more difficult to take off than any of the manual transmission cars I've owned. Sometimes the engine just seems to have a mind of its own and suddenly cuts out as I release the clutch.

Just for fun I was watching the eLSD display, and I noticed the eLSD wheel slip % spikes and turns red at the same time the engine feels like it's cutting out. It seems likely there is a bug in their wheel slip % calculation that causes the ECM to suddenly pull power unnecessarily. To be clear, this happens even when I barely take off and there is ZERO slip. In fact, the more you slip the clutch to take off, the more wheel slip the eLSD display shows.

This also may be related to why the launch control sucks so bad on the manuals. People usually slip the clutch to take off hard and also avoid bogging or spinning. If the car thinks the wheels are spinning when they're not and pulls power, that would cause the car to behave similar to when the car pulls power due to torque management.

Does anyone know exactly how this wheel slip % is calculated? It certainly doesn't align with the traction control wheel slip indicator in any way.

I agree that the eLSD appears to be uber-sensitive and may be contributing to miscalcuations in the traction and/or stability control subsystems. However, I believe the primary cause of poor launches is the "Manual Transmission Protection" feature (bug) described in GM Doc ID 4733151. This control cannot be turned off at all. It is hard-coded into the ECM firmware. Although the same routines appear to be used to "reduce engine power" under certain conditions of various drive modes (HP Supplement pg 27), neither disabling the nannies by holding down the SC button or even pulling the ABS fuses to completely disable TC/SC will turn off this feature. Believe me I have tried...

Originally Posted by travislambert

I thought I'd post the summary I sent GM on June 25th in case anyone is interested.

Beyond the acknowledgement of the email, I haven't received anything. I'll keep you guys posted.

I like how you wrote-up the issue like a software bug report - very thorough.

I didn't get to the track yesterday due to weather (again) but I went ahead and took my M6 out for a drive with the eLSD display in the DIC to see if I could duplicate your findings. I started out in drive mode "Track" with handling mode "Race" to minimize any drive/handling mode interference.

First off, I found it odd that I got 1% to 5% spikes while idling and revving the motor in the driveway - in neutral or 1st gear w/clutch in.

Even timid driving in a straight line with no high-power launches seemed to bump the slip %, sometimes as much as 20% at higher RPMs. At no time during this portion of the test did I detect any actual wheel slip at all.

Spirited driving in Race mode with high-power launches and hard acceleration made the indicator go wild. As expected, I observed high slip values just as I sensed the slightest wheel slip, whether left or right or both. There did not appear to be any interference from the eLSD to control this slip by clamping down on the half-shafts. Neither could I correlate any engine timing retardation to the eLSD readings. I detected no engine power loss during this portion of the test - only momentary loss of acceleration when wheels spun. I kept the launch RPM below 3500, working the clutch to try some zero-spin and some slight spin starts.

Spirited driving in "Sport 1" mode with high-power launches and hard acceleration behaved similarly with high spikes in eLSD slip readings, except that there was far less actual wheel spin. This is what I expect of the eLSD - to intercede only enough to keep the wheels planted. Sport 1 mode is the lowest (least intrusive) handling mode that still employs Stabilitrak which activates the eLSD to control wheel slip.

I did not try the lower drive/handling modes because they more aggressively reduce engine power by retarding the timing. Although I did not record this testing and it is admittedly unscientific, I'm convinced that the primary cause of nose-dive launches and poor 60 ft times & 1/4 mile ET's is the "Manual Transmission Protection" feature. Its main purpose is to protect GM from warranty claims IMO.

As a road track racer the 6th Gen ZL1 M6 reigns supreme. No other car in this price range offers more bang for the buck - especially for those of us who crave the challenge of managing the gearbox. As a drag strip racer, this car requires an ECM tune to be competitive. Competitive or not, I'm still going to have fun with it.

--Cal

[bmlocal175]

So as a buyer in the future and someone who will never track or drag this car, should I be concerned with this problem with the M6? Will it bother me with drives on the weekend or a trip around town?

[cwebster]

Originally Posted by bmlocal175

So as a buyer in the future and someone who will never track or drag this car, should I be concerned with this problem with the M6? Will it bother me with drives on the weekend or a trip around town?

No. This is not a driveability issue. It's a performance issue. If you pull up next to a Viper or Ferrari at a stop light and decide to show-off, you might embarrass yourself but that's about it.

[travislambert]

Originally Posted by cwebster

No. This is not a driveability issue...

I'm sorry, but I don't agree with this. I have caught this car in the act with a laptop pulling 20+ degrees of spark timing going less than 2 MPH just trying to take off gently. That can make the car difficult to drive.

The daily driveability issue is the real reason why I started this thread, and numerous life-long manual drivers have stated that this car is the most challenging manual transmission car they've ever driven (myself included).

I'm pretty sure it all boils down to the fact that GM uses a percentage of wheel slip. At low speeds a little bit of error or actual slip will cause high spikes in the "Wheel Slip %" (because the car is barely moving and as a percentage, the slip is significant.) The car sees a value like "400%" wheel slip, panics, and pulls timing even though the car is barely moving. This is of course, with the nannies on.

The dragstrip launch issue, may or may not be related, but I'm guessing it falls short for the same reason. When using launch control the car is managing wheel slip to try to keep the car's rear wheel speed within 5%-15% of the front wheel speed. At low speeds, using a percentage bites them in the butt because it doesn't give the car any wiggle room to take off. When you first drop the clutch the rear tires are going to slip a little. If the front isn't moving yet, well that's infinitely more slip than is allowed.... and there goes your timing.

I think this is why the double-clutching method of launching has a chance to work. Once you drop the clutch the car lunges forward, the computer pulls timing, but by pressing in the clutch again the computer puts the timing back immediately instead of phasing it in slowly. When you re-engage the clutch, you're already moving so the Wheel Slip % calculations are more accurate, and you've effectively avoided the delay in the computer phasing the timing back in.

Without launch control enabled and the other nannies off, the car feels like (very unscientific) it's still trying to help me get traction by pulling timing. I'm not sure why. I can't explain that unless the PTM is simply never fully disabled.

[cwebster]

Originally Posted by travislambert

I'm sorry, but I don't agree with this. I have caught this car in the act with a laptop pulling 20+ degrees of spark timing going less than 2 MPH just trying to take off gently. That can make the car difficult to drive.

The daily driveability issue is the real reason why I started this thread, and numerous life-long manual drivers have stated that this car is the most challenging manual transmission car they've ever driven (myself included).

I'm pretty sure it all boils down to the fact that GM uses a percentage of wheel slip. At low speeds a little bit of error or actual slip will cause high spikes in the "Wheel Slip %" (because the car is barely moving and as a percentage, the slip is significant.) The car sees a value like "400%" wheel slip, panics, and pulls timing even though the car is barely moving. This is of course, with the nannies on.

The dragstrip launch issue, may or may not be related, but I'm guessing it falls short for the same reason. When using launch control the car is managing wheel slip to try to keep the car's rear wheel speed within 5%-15% of the front wheel speed. At low speeds, using a percentage bites them in the butt because it doesn't give the car any wiggle room to take off. When you first drop the clutch the rear tires are going to slip a little. If the front isn't moving yet, well that's infinitely more slip than is allowed.... and there goes your timing.

I think this is why the double-clutching method of launching has a chance to work. Once you drop the clutch the car lunges forward, the computer pulls timing, but by pressing in the clutch again the computer puts the timing back immediately instead of phasing it in slowly. When you re-engage the clutch, you're already moving so the Wheel Slip % calculations are more accurate, and you've effectively avoided the delay in the computer phasing the timing back in.

Without launch control enabled and the other nannies off, the car feels like (very unscientific) it's still trying to help me get traction by pulling timing. I'm not sure why. I can't explain that unless the PTM is simply never fully disabled.

Sorry, not trying to minimize your driveability issues. I just have not experienced what you are describing with the low-speed power loss. I very seldom use Touring mode so maybe that's why I haven't seen it. Most of the time I'm in "Track" drive mode with either the default (Wet), Sport 1, or Race PTM mode depending on conditions. It's possible that my senses are not keen enough to pick up on it. It's also possible that the issue does not affect all M6's. For me, there are no driveability issues at all. You asked for input... that's what I've experienced.

--Cal

[Infern0]

Originally Posted by cwebster

Sorry, not trying to minimize your driveability issues. I just have not experienced what you are describing with the low-speed power loss. I very seldom use Touring mode so maybe that's why I haven't seen it. Most of the time I'm in "Track" drive mode with either the default (Wet), Sport 1, or Race PTM mode depending on conditions. It's possible that my senses are not keen enough to pick up on it. It's also possible that the issue does not affect all M6's. For me, there are no driveability issues at all. You asked for input... that's what I've experienced.

--Cal

That's interesting. When you say most of the time you're in track mode, does that mean you're usually at the track, or you daily drive in that mode?

I have noticed a slight difference between daily driving in sport and touring, though I haven't done it enough to really describe it, just that it crossed my mind at the time. I also didn't put any thought in to it because I thought it was coincidence, thinking those modes didn't impact actual drivability other than steering, suspension, and sound. Though I've never tried to daily drive in track.

[travislambert]

Originally Posted by cwebster

Sorry, not trying to minimize your driveability issues. I just have not experienced what you are describing with the low-speed power loss. I very seldom use Touring mode so maybe that's why I haven't seen it. Most of the time I'm in "Track" drive mode with either the default (Wet), Sport 1, or Race PTM mode depending on conditions. It's possible that my senses are not keen enough to pick up on it. It's also possible that the issue does not affect all M6's. For me, there are no driveability issues at all. You asked for input... that's what I've experienced.

--Cal

That's interesting. The daily driver portion of the issue has been a little tough for me to nail down.

There have been at least a few ZL1 M6 owners say they haven't yet experienced the daily driver issue. I know at first, I was blaming myself thinking I wasn't being smooth with the clutch. It wasn't until later I realized it was the car and not me. But in my mind, I'm not satisfied that a difference in perception is the only explanation.

I too have considered the potential for software differences. I also think road conditions play into it a little. It's more easily reproducible on a hill. So people who mostly drive on flat roads are less likely to have the issue. Also, a small amount debris, gravel, etc. will cause the rear wheels to slip a slight amount and the car will nearly stall even though it's barely slipping. In WV, we have lots of hills and debris on the roads, so maybe it's just the perfect storm here.

I certainly appreciate your input though. The more input we get the easier it'll be to narrow the problem.

[travislambert]

Just for fun I pulled a frame from the MT ZL1 vs GT 350R review immediately after the start of the drag race.

Notice how the Mustang completely embarrasses the ZL1 off of the line? It's not simply due to the fact that the GT350R weighs less, because the Challengers embarrass the ZL1s off of the line too.

Also, notice how the Mustang effectively transfers weight to the rear wheels? The M6 ZL1 is just the opposite with it's nose dive stance immediately after launch.

I'm not exactly sure why MT didn't call attention to this. My guess is they assumed it was the driver's fault, even though we all know that's probably not the case.