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I ran my car at VIR on Wednesday and Thursday. Wednesday the car ran great. Thursday during the third session on around the 10th lap I lost power. It felt just like ptm kicking on when I stepped on the throttle.It made that same machine gun sound and had very little power.I drove back to the pits and let it set for about 10 minutes and it did the same thing even in touring mode.
I decide to call it a day and loaded it back on the trailer and pulled it home. When I got home a couple of hours later it seemed ok.
My temps were as follows
Coolant 208
Oil 259
Trans 221
Oat was around 79
Any ideas on what caused it? Thanks in advance.
Last edited by badhabit_wb; 04-01-2018 at 07:04 AM.
What mods do you have other than the aftermarket throttle body? What year Z?
I assume you do not have the DSC, correct?
I have the DSC module and tractive shocks,Tony Mamo throttle body and MGW shifter. I've also got Girodisc rotors and st-43 pads. I've also installed Racetech seats. The only reason I mentioned the seats is I do have a constant light because of the airbags.
I don't hear PTM kicking in anywhere but I'm going to guess that you felt it when you went back to WOT exiting T3 (roughly 25:10 in the video)? The data trace definitely shows the torque output is about 100 lb/ft lower than previous laps but you are also a little slower and as a result at a lower RPM but that's not enough to explain that big a drop.
Unfortunately you don't really go WOT much after that so it's tough to see a longer term problem. It looks good when you go to WOT briefly entering the lower esses but is also about 100 lb/ft off when you go WOT again under the bridge.
I suspect you either have some knock retard going on from bad gas or it could be a catalytic converter going bad. I went through two of them on my 2015 C7Z and the symptoms were the same as you are seeing. In my case both of them were cracked and one of them was blowing exhaust gas on the knock sensor.
I don't hear PTM kicking in anywhere but I'm going to guess that you felt it when you went back to WOT exiting T3 (roughly 25:10 in the video)? The data trace definitely shows the torque output is about 100 lb/ft lower than previous laps but you are also a little slower and as a result at a lower RPM but that's not enough to explain that big a drop.
Unfortunately you don't really go WOT much after that so it's tough to see a longer term problem. It looks good when you go to WOT briefly entering the lower esses but is also about 100 lb/ft off when you go WOT again under the bridge.
I suspect you either have some knock retard going on from bad gas or it could be a catalytic converter going bad. I went through two of them on my 2015 C7Z and the symptoms were the same as you are seeing. In my case both of them were cracked and one of them was blowing exhaust gas on the knock sensor.
Yeah I was afraid to get on it too hard with the reduced power. The exhaust just sounded strange at full throttle.I'll jack it up when I get back home on Monday and see if the converter is cracked. The only fuel I've used in it came from VIR so hopefully that's not the issue.
Thanks for checking that out. It gives me a good starting point. I don't have a lot of confidence in the dealership but they'd probably let me swap out the converters if that's the issue.
Thanks again for helping.
That sucks, look for loose or broken wires especially around the exhaust and 02 sensors. Years ago a guy here had a cracked wire that was bouncing off his exhaust and caused erratic similar issues. We have a Snap On Solos scanner that allows you to watch 02 and cylinder spark. Finding something similar at a shop may help a lot and some will pull memory of data when it happened.
Good luck and very interested in what it is or was.
Poor-sha what cats cracked on your 15 up stream or down? Were they rapped?
That sucks, look for loose or broken wires especially around the exhaust and 02 sensors. Years ago a guy here had a cracked wire that was bouncing off his exhaust and caused erratic similar issues. We have a Snap On Solos scanner that allows you to watch 02 and cylinder spark. Finding something similar at a shop may help a lot and some will pull memory of data when it happened.
Good luck and very interested in what it is or was.
Poor-sha what cats cracked on your 15 up stream or down? Were they rapped?
Thanks I'll check that. I have a Mongoose pro that I think will do that as long as I have a GM subscription.
I hope it's just a loose wire. It seemed to run fine at home but it's hard to tell on the street.
Poor-sha what cats cracked on your 15 up stream or down? Were they rapped?
I'm pretty sure the first one was the up stream cat. I actually never saw the second one, they just replaced it. I believe the car had a 3rd one going when I sold it to get the 2017 as it was exhibiting similar symptoms.
The problem is that the next morning it would run fine and it wouldn't start having issues again until you got it really hot on track. I figured out it was a cat because eventually it got so bad that you could hear the "tick-tick-tick" of an exhaust leak under the car at idle. The crack was on the top of the cat so it wasn't really visible and I think it opens up when the cat gets really hot so it's hard to see even if it wasn't on the top.
I'm pretty sure the first one was the up stream cat. I actually never saw the second one, they just replaced it. I believe the car had a 3rd one going when I sold it to get the 2017 as it was exhibiting similar symptoms.
The problem is that the next morning it would run fine and it wouldn't start having issues again until you got it really hot on track. I figured out it was a cat because eventually it got so bad that you could hear the "tick-tick-tick" of an exhaust leak under the car at idle. The crack was on the top of the cat so it wasn't really visible and I think it opens up when the cat gets really hot so it's hard to see even if it wasn't on the top.
I've got a usb camera that I can look at it with. I know the motor has to be raised a little to get the pipe off but it shouldn't be too big a deal. Was it both upstream when it happened or just one of them? Driver or pass side if only one? I'm guessing it's still under the 5 year warranty on a 15.
Was yours wrapped?
One at a time. As I recall it was the driver side the first time. I don't know which the second one was.
Thanks. I'll try to figure out which one it is on Monday. I called the dealer and there was some concern about being able to re-create the issue. I told them I had the video from the pdr. They said they wanted to make sure it was under warranty if it only happened on the track. Hopefully mine has a crack that I can see. If so that will make it easy.
Sean you got me interested in the Pi toolbox. I compared lap 9 and 10. Coming out of the turn at Oak Tree I had 643 ft lbs of torque at full throttle on lap 9 and only 263 ft lbs of torque at full throttle on lap 10. Unless I set up the toolbox wrong something is definitely off.
...They said they wanted to make sure it was under warranty if it only happened on the track...
I had a catalytic converter problem on my C6 ZR1 a few years ago, and the car was out of warranty.
I had a big limp mode loss of power on the track when accelerating through exactly 5,000 rpm. I took it to the dealer and after a couple days they called and said come pick it up - they couldn't find anything wrong. They said they test drove it and it drove great.
I went back to the dealership and told the service guy to get me the car and the tech, because I wanted to show him the problem. The tech got into the right seat and hooked up a computer to the OBD port, and I took it out and stepped on it - and at 5,000 rpm the car virtually died. The tech said "Oh - I didn't rev it like that on the test drive I did!"
They did some coordinating with the Tech Center and determined that it was a cat problem and ordered a new cat for the side that had the problem. When it came in they found that Chebie had changed the exhaust a bit from year-to-year and my x-pipe wouldn't fit on the new cat. So, they had to order a new cat for the other side and a new x-pipe as well.
I was expecting a HUGE ransom to get the car back, but was i surprised when they gave me the bill - it was ZERO $$$!!!
It turns out some stuff related to emissions is apparently covered by a federal law that gives the cats, among possibly some other items, a warranty separate from the car. My cats were covered by an 8 year/80,000 mile warranty!!!
So...if you do have a cat problem, it may be covered by that extended emissions warranty.
I had a catalytic converter problem on my C6 ZR1 a few years ago, and the car was out of warranty.
I had a big limp mode loss of power on the track when accelerating through exactly 5,000 rpm. I took it to the dealer and after a couple days they called and said come pick it up - they couldn't find anything wrong. They said they test drove it and it drove great.
I went back to the dealership and told the service guy to get me the car and the tech, because I wanted to show him the problem. The tech got into the right seat and hooked up a computer to the OBD port, and I took it out and stepped on it - and at 5,000 rpm the car virtually died. The tech said "Oh - I didn't rev it like that on the test drive I did!"
They did some coordinating with the Tech Center and determined that it was a cat problem and ordered a new cat for the side that had the problem. When it came in they found that Chebie had changed the exhaust a bit from year-to-year and my x-pipe wouldn't fit on the new cat. So, they had to order a new cat for the other side and a new x-pipe as well.
I was expecting a HUGE ransom to get the car back, but was i surprised when they gave me the bill - it was ZERO $$$!!!
It turns out some stuff related to emissions is apparently covered by a federal law that gives the cats, among possibly some other items, a warranty separate from the car. My cats were covered by an 8 year/80,000 mile warranty!!!
So...if you do have a cat problem, it may be covered by that extended emissions warranty.
.
Thanks! I'm out of town until tomorrow but when I get home I'm going to try to figure it out. I think once I have it narrowed down it will be easier to convince the dealership. Hopefully it will be something obvious.
03-30-2018, 11:57 AM
Reduced power on Track
