Brandi05vette

Took my car to the drag strip. When I shift into second gear it feels like my car is dropping cylinders and losing tremendous power until I hit around 5800-6000 rpm and then it comes back to life. I keep power in all other gears. This is only happening when I am at the track and the car hooks hard through first gear. The car was tuned originally by Breathless Performance in Ft. Lauderdale FL but I have changed the tune to see if we could fix the problem but so far no luck. The traction control is not on and we disabled the wheel hop with LS2 edit.

I have a 06 Z06 with Vararam Cold Air Induction, Kooks headers with off road X pipe, and Hurst Short Throw Shifter.

Any Ideas

9sec383

It sounds like its pulling timing for some reason...maybe crappy gas??
You might wanna get it dynoed on a mustang dyno to load it and check your tune.....hope that helps
Lopez

Brandi05vette

It was dynod on a Mustang Dyno. It only does it at the track and only in 2nd gear. I agree I do think it is pulling timing out of the car. Any other ideas?

TTZ06VETTE

+1 for timing. What are your IAT's? Is it possible high IAT's are causing timing to be pulled? Any Kr happening that would cause default to low octane timing table? Really need a scan or more info to know for sure.

ipmtim

could be torque managment pulling timing

Geared

honestly sounds like t/c is kicking in.....try disabling the entire system?

355Spider

That's exactly house torque management works.

KLLRVET

make sure the clutch pedal is contacting the upper clutch switch. I chased this problem for two years. if the pedal does not fully engage the switch, reset the depth of the switch.

06-Z0SICK

A log would be best an eliminate a lot of possibilities if u can have one done while its happening.

KLLRVET

Does the car like you are hitting the rev limiter right after the 1-2 shift?

Brandi05vette

The torque management was disabled with the dyno tune....the thing that I don't understand is why does it only do it in 2nd gear and not 3rd or
4th....I have looked everywhere on the LS2 edit and can't see anything else to do to fix the problem....I will check on the clutch pedal....would it only do it in 2nd if that were the case....thanks everyone for your ideas...I hope I can figure this out....it can drive you crazy

thesubfloor

There's a secondary rev-limiter kicking in which (under HP Tuners at least) is under fuel control and is called "Accel Thresh" which is the PCM's way of keeping the car from overshooting the rev-limiter when it accelerates too fast. It usually happens when you put gears or a stall converter in an automatic and can be turned off.

Ranger

I'd suggest that you have a conversion with the shop that tuned your PCM. The tech there should be very familiar with the inter-relationships among tables in the PCM and their individual and collective impact on power and power-adjustments at shift transitions.

But I must add that if you want diagnostic help here, you ought to post explicit step-by-step descriptions of driver actions from initial launch through the aftermath of the 1-2 shift. All the details.

1. What tires are on the car? At what rear PSI?
2. What launch rpm?
3. What clutch release?
4. What's the 60'?
5. What does the clutch pedal do after the launch?
6. Are you losing power at 6300-6500 before the 1-2 shift?
7. If not, at what rpm are you initiating clutch-in?
8. Are you power-shifting the 1-2?
9. What does the clutch pedal do at the hit of the clutch post-shift on the 1-2?
10. What is the 330' time"
11. Are you data-logging the PCM during the pass?
12. How many passes at the track have you made in this car? In similar cars?

Answers to those, organized by question, would give someone a place to start diagnosing.

You'll need to give the tuner the same info anyway.

Ranger

Brandi05vette

[QUOTE=Ranger;1576471652]I'd suggest that you have a conversion with the shop that tuned your PCM. The tech there should be very familiar with the inter-relationships among tables in the PCM and their individual and collective impact on power and power-adjustments at shift transitions.

But I must add that if you want diagnostic help here, you ought to post explicit step-by-step descriptions of driver actions from initial launch through the aftermath of the 1-2 shift. All the details.

1. What tires are on the car? At what rear PSI? Bridgestone Radials (not run flats) rear PSI is at 26lbs
2. What launch rpm? 3,000
3. What clutch release?
4. What's the 60'? 1.7
5. What does the clutch pedal do after the launch? feels normal after launch
6. Are you losing power at 6300-6500 before the 1-2 shift? no loss of power before the shift
7. If not, at what rpm are you initiating clutch-in? we have tried several shift points but normally shift around 6700 rpm
8. Are you power-shifting the 1-2? we have tried both ways and the problem is the same whether or not you power shift of not
9. What does the clutch pedal do at the hit of the clutch post-shift on the 1-2? normal
10. What is the 330' time" 4.861
11. Are you data-logging the PCM during the pass? we have not as of yet but we just recently got the program to scan it during the pass so that data should be coming
12. How many passes at the track have you made in this car? In similar cars? about 20 passes in this car and then 20 or so in an 10 z06 and the 2010 is having no issues...the car will have the same issue on the street if it hooks

Answers to those, organized by question, would give someone a place to start diagnosing.

You'll need to give the tuner the same info anyway.-
I spoke with the tuner and he is at a loss...He said that he has never heard of this problem before.Thanks to everyone for your responses and ideas!

Joe_G

This happened to me as well, and is why I've taught myself HP tuners.

You should have your car scanned with HP tuners while this is going on. If you are close to PBIR I will be there Wednesday and would be pleased to help.

Ranger

[QUOTE=Brandi05vette;1576473490]1.7X

What was the 60' time exactly.

Provide the rest of the time slip values.

60'.............
330'...........
660'...........
660’ mph...
1000'..........
1320'..........
1320’ mph…

Ranger

Brandi05vette

[QUOTE=Ranger;1576473679][QUOTE=Brandi05vette;1576473490]

1.7X

What was the 60' time exactly.

Provide the rest of the time slip values.

60'.............1.778
330'...........4.861
660'...........7.345
660’ mph...100.37
1000'..........9.444
1320'..........11.209
1320’ mph…128.22

This is from my best time slip with the problem occuring

Brandi05vette

Where is PBIR...sorry I am not familiar with that...thanks

Joe_G

As I recall Retrotech had a similar issue with his 07 Z when he power shifted. Will see if he ever got it solved.

Christopher I just looked at Retrotech's Z tune, the acceleration threshold table is not there like it is in my 05 tune. Might be somewhere else in the tune, I didn't spend much time looking except where it is under my tune.

Ranger

The rev-limiter does not prevent the rpm from sailing past the 7120 or 7200 limiters during clutch-in on a shift. That's because clutch-in at 7000 removes a huge mechanical burden from the flywheel, creating a transitory mechanical pop in rpm to 7300-7450, depending on throttle position at clutch-in. It lasts only the duration of clutch-in to clutch-out.

That's knowledge caused me to change my shift procedure.

Don't believe this manifestation is necessarily related to the OP report. But it does reflect info that's not widely appreciated.

Ranger