Quote:
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.
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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...
Quote:
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.
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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