jrizzuto

Hi 2017 A8 owners (only 2017 owners). Need a favor. If you have a PDR option, do this please...

First startup in the morning...
1 - start the car
2 - immediately go to the PDR function
3 - hit record
4 - go in reverse....back up a little (or out of your garage)
5 - go in drive...go a little
6 - stop recording

Then...review the recording. See if when you shifted to DRIVE, does it show you went to 4th and then 1st, or did you go directly to 1st.

Please let me know, much appreciated. Once I get some responses, I'll explain why I am asking for this.
Jim

jrizzuto

OK since so many fellow corvette owners jumped on this so quickly, let me adjust the ask.
Late 2016 A8 or 2017 A8 owners. The key is to capture this with the newer version A8.

Please?

C 5

What is the purpose of this test? What is being tested or seen?

NSC5

I wouldn't be surprised if it briefly indicates 4th gear before shifting into 1st since 4th is the default "limp" gear. If you have one of the non-updated Range modules it will randomly cause a communications error for the TCM and the transmission goes into and stays in 4th gear when drive is selected due to the loss of communications.

My 2016 Z06 was produced March 2016; I can do a PDR recording tomorrow if nobody posts up prior to that time.

jrizzuto

Thanks. My purpose for this experiment is this....I unfortunately have one of those bad A8s. Stator replaced, issue remains. One day I recorded my morning start to show how the car lurches from R to D. To my surprise, when I shift to D it went to 4th (smooth) and then lurched to 1st.
SO I wanted to see if the new model A8 does the same thing. If it does, then my theory is dead. If the new model A8 goes direct from R to D 1st, then I may have made a discovery about the older A8s.
Appreciate anyones time who does this for me.

NSC5

It will be later in the day tomorrow before I have a chance to do the PDR recording but I will check it and let you know by tomorrow afternoon. I have an early morning meeting at a place where I don't want to park the Z06.

My March 2016 build A8 has been perfect except for the one Range AFM glitch that happened while on a trip to TN and that was cured by a restart. It is purely a Range issue which is cured by their update. Otherwise my A8 has been very smooth both warm and cold. I do let the Z06 drop to base idle (maybe 20-30 seconds max) before putting it into gear from a cold overnight start.

cam30era

I recorded the video, and drove for about 60 seconds, but it's too large to upload, even if I zip it. May, 2016 build date. Observations: when shifting into Drive there's a split second display of "4" then "1". My car has about 2,000 miles on it. Shifts into drive as one would expect. Nothing unusual, at all. No bang, clunk or learch.

Let me know if you need any other information.

jrizzuto

Perfect. So I see when you shifted to D it went from 4th to 1st...but in a split second. Mine stays in 4th for 1-2 seconds then bangs into 1st.
Any experts care to comment? I can't imagine why it goes to 4th at all.

cam30era

FWIW, despite what the gear display shows, it's not obvious that it's really doing anything other than going directly to 1st on my car. It feels like it's going directly to 1st, and I doubt that an electro/hydraulic/mechanical system could react that fast. My guess is that it's just a display anomaly (in my case).

NSC5

I just took a short drive with the PDR operating. From a cold start it of course shows P and then R once I chose reverse. When I shifted into Drive the N flashes briefly on the PDR video as the selector passes through neutral on the way to drive but then it immediately shows 1 without flashing up 4. This is a 2016 Z06 A8 that came off the line on March 8 2016 and was picked up at the museum on March 25. There have been no updates applied since I bought it and I still need to take it in for the airbag software update.

cam30era

My 2016 Z51 showed just a split second of "4" before "1". And I literally mean the blink of an eye. Would be very easy to miss it, if one isn't intently watching that part of the display.

NSC5

Interesting, that was on the PDR video-correct? I just dumped the PDR video into Movie Maker which allows you to slow playback to 1/8th speed and also view it frame by frame and mine never shows 4 instead transitioning from N directly to 1. According to the timing marks in Movie Maker it shows N for just over 80 milliseconds before showing 1.

cam30era

Yes, correct. And FWIW, I don't believe that it was actually engaging 4th for such a short interval.

NSC5

I believe you are correct that it isn't actually going into 4th.

One difference might be that this was a cold start for the Z06 and I let it warm up for about 30 seconds before placing it into gear. There is a lot of traffic on the CAN bus right after initial startup and as I noted earlier in the thread and if there is a communications error with the TCM the default in drive is 4th gear. How long was your car running before you put it into gear? It is possible with the bus busy it might briefly show 4 before the TCM successfully concludes communications with the other controller when there is heavy network traffic.

I would test this hypothesis but the nearby farmer is starting to harvest beans so the Corvette is back in the garage under its dust cover and I am taking my daughter to soccer in the ATS so the C7 won't be out anymore today.

cam30era

It was also about 30 seconds. You can see the video is the link I posted above.

NSC5

It is interesting that your PDR video doesn't flash up N like mine does on the way from R to Drive. If I get a chance over the weekend I will try mine a few more times to see if it consistently shows N instead of 4.

jrizzuto

Thanks to everyone doing this. Like I said, I have the older A8 plagued with the morning lurch. When I saw this in my PDR, in my head I said "BINGO".

I can tell you that when I go from R to D, it does show 4th for a second or two and then slams into 1st.
But while it is allegedly in 4th, it not engaged...the car can roll as if in neutral.

So the difference between the new vs. old A8 is the time it spends in 4th is a nano second, where as mine spends a second or two.

Interesting.

cam30era

Welcome. Now the question is, what can you do with this information?

jrizzuto

If I could talk to a GM engineer (or someone at expert level) I would ask the following:
1 - Is it intentional that R-D stops in 4th before going to 1st? It doesn't do that any other time other than a cold start.
2 - could the morning lurch problem have anything to do with it sitting in 4th for 1-2 seconds before it goes to 1st?
3- How come newer A8s done't dwell in 4th - hence they don't exhibit the delay or the lurch.

After all without the PDR, this would never even be visible, so perhaps no one ever noticed. I'm just stubborn I guess, there has to be a reason why my older A8 has a problem and your newer A8 doesn't. GMs fixes thus far have not been successful for everyone.

Again - thanks.

NSC5

This is the best breakdown I have seen for the power flow through the 8L90 showing both via diagram and text description how the various ratios are selected. It probably won't help much with your current "project" but maybe some of the information will be useful: http://www.thetruthaboutcars.com/201...-transmission/