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Old 09-16-2019, 07:37 PM   #1
Jimabe
 
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A10 shifting problem after mods

Just completed second set of mods giving me a little over 700 whp. List of mods in signature.

No changes or tuning done to the transmission. Had car back from tuner and drove 4-5 times. Did plenty of manual shift WOT sessions and in “D” WOT hits w/no issues.

Was giving buddy a ride and had in manual mode near redline and car had an “event” that lost drive and over revved engine. Did multiple times. Majorly scary. Thought blew something up at first. Car idled, ran and shifted fine immediately after while driving easy. No leaking fluids, mechanical noises or service lights.

Let it sit to cool down at work and on trip home figured I’d give brief WOT run in D and see what happens. Was in D, going about 25, then went WOT. Didn’t make it to next shift point and had same event.

Took to tuner and it repeated for him. Says car is actually downshifting instead of upshifting while near red line. Said rpms flashed to 7500 then rev limiter takes over and tries to shut down. Certainly VERY concerning. He is going to try and trouble shoot.

Has anyone had any experience like this? Almost seems like a transmission programming thing gone wrong.
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Old 09-16-2019, 07:47 PM   #2
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pretty basic mods... sounds like your tuner messed something up.

Where did you take it, and do they have a lot of history tuning the LT$ and the LT4 A10 combination?
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Old 09-17-2019, 08:10 AM   #3
Jimabe
 
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Yes, he has. The Trans CM wasn't touched. It also drove OK for a brief period after i picked it up. Can something in the ECM Tune make the tranny downshift instead of upshift? Not sure where the Programming resides that makes the A10 shift...

The weird thing is it shifts normal under light and normal acceleration, but only does this up at the big end...
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Old 09-17-2019, 10:37 AM   #4
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I don't know much about modding but would think everything that can be tuned should when going up in significant hp??
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Old 09-17-2019, 10:55 AM   #5
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Seems like 7500 is pretty high for this motor, 1000+ over. If it does it again, dont let it repeat, stop revving anywhere near red line until it's fixed. You will bend valves from float. I dont understand why OEMs dont always use high rev springs with 9-10K RPM capability on car like this to avoid that kind of damage, keeping rev limit 3k RPM below the spring's capability. This might cost them an extra $100 to include.

I'm surprised you're able to rev that high and it sounds like you're saying it does it while holding full throttle/load past 7000 RPM. My rev limiter always kicks in immediately at 6400 RPM when I hit it with my manual, and the RPMs fall immediately with no power. My ECU shows no over-revs.
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Old 09-17-2019, 11:26 AM   #6
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Quote:
Originally Posted by SFV1LE View Post
Seems like 7500 is pretty high for this motor, 1000+ over. If it does it again, dont let it repeat, stop revving anywhere near red line until it's fixed. You will bend valves from float. I dont understand why OEMs dont always use high rev springs with 9-10K RPM capability on car like this to avoid that kind of damage, keeping rev limit 3k RPM below the spring's capability. This might cost them an extra $100 to include.

I'm surprised you're able to rev that high and it sounds like you're saying it does it while holding full throttle/load past 7000 RPM. My rev limiter always kicks in immediately at 6400 RPM when I hit it with my manual, and the RPMs fall immediately with no power. My ECU shows no over-revs.
A HR lifter still has it's limitations and seat pressure can only be so much.
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Old 09-17-2019, 12:24 PM   #7
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Originally Posted by 396ssrat View Post
A HR lifter still has it's limitations and seat pressure can only be so much.
Yes, wasn't assuming they put in springs that dont match other basic components needed to handle a rare over-rev event. Maybe what all the good shops do when they upgrade springs and lifters, at least to handle a mishap like mechanical over-rev with a manual or whatever the OP is describing here.

Even if the engine isn't designed and tuned to go to 7500-8000 it would be good to have a safety buffer if it did.
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Old 09-17-2019, 12:25 PM   #8
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99% chance this is on the Tuner. 1% bad Tranny.

There's been reports from the 1/2 milers with 3-4 and 4-5 hangs (doesn't shift, bounces off limiter) but this is the 1st I've ever heard of a money-shift from an automatic.
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Old 09-17-2019, 02:38 PM   #9
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Quote:
Originally Posted by Gunkk View Post
99% chance this is on the Tuner. 1% bad Tranny.

There's been reports from the 1/2 milers with 3-4 and 4-5 hangs (doesn't shift, bounces off limiter) but this is the 1st I've ever heard of a money-shift from an automatic.
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Old 09-17-2019, 03:13 PM   #10
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Isn't this pretty simple to test? Have tuner flash ECM back to stock...see if issue goes away.
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Old 09-17-2019, 07:49 PM   #11
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I private message you I have exact problem n can not figure please let me know what you come with
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Old 09-18-2019, 06:49 AM   #12
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I've talked w/SUPER SS and our issues are almost exactly the same. Very similar mods, his didn't happen right away after the last tune, he gets a "money shift" in manual or "D" mode...All the same. His is a '17 A10 and mine is a '18 A10. Obviously different Tuners. SUPER SS hasn't figured out a fix yet, same as us, but just putting it out there, there are 2 instances of this...

Don't know what's causing it yet so could be a ton of things (Tune, Trans, programming, etc). Obviously there are a ton of people on here who have similar mods w/no problems, so going to be tough solve I think. Once we find a fix, will post to potentially help others.
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Old 09-18-2019, 09:08 AM   #13
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Thanks for posting so we can all learn. What is your next step, unlocking/tuning the trans?
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Old 09-18-2019, 09:48 AM   #14
Jimabe
 
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Not 100% sure at moment, although he's talking w/others in Tuning community, GM Tech contacts and possibly TCM Tuning...
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