Transmission "Grabs" When Stopping

[OZPower]

So it appears after the cam install there are a few issues with the car and I'm just trying to get some ideas before the car goes back to have the computer checked because it went into "limp" mode after I drove it for like 100 miles that day so not sure what it saw but that part I think can be figured out by looking at the codes.

Basically, when coming to a stop leaving the car in drive mode once you get down to like 15 mph(ballpark don't know exact) it feels like the trans grabs and lugs the motor down and then it lets go and then grabs again and lets go and then the car comes to a stop. I don't have the exact spec on the cam, but its nothing too insane.

So, is this something with the convertor (I've been told its a little tight and an adjustment can fix this) or is this something in the torque management, etc? I had the convertor in the car before I had the cam and it did fine.

I'm not looking to set the world on fire at the track I'd just like to have the driveability without the car doing this everytime I go to stop at a traffic light...

Any help would be appreciated.

[Matt]

Maybe what your feeling is the downshift to first. Since your idle is probably raised a little with the cam tune its more noticable now.

[OZPower]

Well, if it is a downshift to 1st then I can understand it doing it once, but why the second time right before it does stop?

The idle I was told was moved from 500 to 650 I believe.

So even if it is part of that downshift can you adjust something to prevent that?

[Matt]

My car did the same thing after the cam install. at about 5 mph or so it would pop out of 2nd and soon as you stop it would surge/buck twice and it would be in first. When in sport mode you can see the gear changes as they happen to correspond with the trans "grabbing". Yes Steve at vector did something with the tune to make it near unoticable now. Call/email him.

[-Ray-]

Matt;
He was tuned by someone local. The tuner needs to fix this.

[OZPower]

When driving the car shifts great and I'd like to avoid pulling the convertor for more than one reason. So, that's why I'd like to figure out what needs to be adjusted in the tuning to resolve it to help save some time on the troubleshooting end of things. I respect my tuner and does great work, but this is the only G8 he has ever done and its a learning curve for him to some extent, and you guys are the best source of information since we have all played with our cars and had our fair share of bugs we've had to work out. Thanks for all the help!

[Devilish34]

If they did not set the idle by speed correctly it will buck as the converter locks and unlocks from dropping to quickly.... 650 target idle seems low to me... Mine is 775....What cam is in your car? Who tuned/installed it bc they need to fix it.

edit what size stall? triple or single disc?

[Matt]

Yea they should fix it. If they can figure it out. Not sure but I think it had something to do with the fuel/timing on that downshift. Not sure tho. Good luck

[OZPower]

If they did not set the idle by speed correctly it will buck as the converter locks and unlocks from dropping to quickly.... 650 target idle seems low to me... Mine is 775....What cam is in your car? Who tuned/installed it bc they need to fix it.

edit what size stall? triple or single disc?

I don't know the exact numbers on the cam I can try and find out. The convertor is a single disc, billet stator, around 3000 stall.

[OZPower]

Cam specs: 222/234 .566 .576 113

(Thats from the box my g/f read to me since the cars in her garage an hour and a half away from me so hope I got it right).

And I'm no cam guru so I don't know how that lines up with others compared to how "mild" it is.

I've been told it could be as simple as disengaging the close TPS torque management, while another source says they don't disengage torque management and I guess just manipulate shift tables to get around it...so its like throwing darts on the wall right now with possibilities and ways around it.

[-Ray-]

There is plenty of info on Hptuners forum if your tuner needs help. Plus several members have shared their tunes on here. You can find 'em if you look.

BTW, you'll need to adjust your sig though. You can mention what shop did your tuning, but you can't have a link in your sig to their shop. Sorry.

[Devilish34]

Cam specs: 222/234 .566 .576 113

(Thats from the box my g/f read to me since the cars in her garage an hour and a half away from me so hope I got it right).

And I'm no cam guru so I don't know how that lines up with others compared to how "mild" it is.

I've been told it could be as simple as disengaging the close TPS torque management, while another source says they don't disengage torque management and I guess just manipulate shift tables to get around it...so its like throwing darts on the wall right now with possibilities and ways around it.

mild IMO

[hulkss]

Your idle will be higher rpm than stock and you will feel the motor push through the stock torque converter when you roll to a stop. Set the idle rpm as close to stock as possible and get used to stepping on the brakes harder.

[JJhummus]

I am having the same issue. We have changed the downshift points, brought first gear up a little to help with most of the issue and I believe that the idle air above 800 needs pulled back a little to help with the last bit of surge. I will be working on this over the weekend, too.... I have roughly the same cam and a stock converter, so I feel your pain.

[OZPower]

And for what its worth I believe the cars tuned with EFI Live not HP Tuners...not sure on the differences or how that might change things with altering settings....

[-Ray-]

And for what its worth I believe the cars tuned with EFI Live not HP Tuners...not sure on the differences or how that might change things with altering settings....

My understanding is that's even better. EFI live has additional trans settings not yet in HPtuners.

[OZPower]

I spoke with my tuner today and he's had some time to think about it and we bounced some ideas back and forth and I feel very confident we can get around the aggressive decel thru the tuning. He said the cam is usually set at 750 in sticks and with the convertor not being as big as some it pushes a little too much at a stop so he backed it down, so putting a little more stall in it would help, but most likely we'll leave it alone.

You guys have been a great help to give us some ideas where to start and some have even offered to take a look at some information which we may need to do, and I thank you all for it.

I will let you know what we figure out...

[Patrick G]

First off, set your idle to at least 750rpm. You can do that even with a stock torque converter so do it with your Pro Torque stall. Next, make sure Torque Management, closed throttle downshifts (D9402) is set to NO.

[G8V8]

Sorry to show my ignorance but what is this "push" some have mentioned?

[-Ray-]

Sorry to show my ignorance but what is this "push" some have mentioned?

When you come to a stop, the rpm's surge and try to push the car through the brakes. excess pedal pressure is required to stop the car. Those who has this issue should be putting it in neutral as they coast until they get the tune resolved. No sense in bumping someones bumper.

[G8V8]

Thanks. Didn't know it had a name. With mine, on braking, when I am almost stopped and the trans is almost ready to downshift to 1st, as the speed drops the rms drop to 500 or a little less then jump to 1000 when it shifts. Then, after it shifts and the rpms have dropped it gives another little rpm blip before settling to idle. If I brake slowly (normally) these actions are much reduced. Braking harder can get interesting. If I lift a little n the brake just about the time I think it is going to downshift, it is much better also. After a couple of tune tweaks, the effects are much less pronounced as my tuners works through it. He is doing a good job of getting just right for me. Sounds like this is somewhat common with cams. A little surprised there is not a common fix.

[pablowest]

So it appears after the cam install there are a few issues with the car and I'm just trying to get some ideas before the car goes back to have the computer checked because it went into "limp" mode after I drove it for like 100 miles that day so not sure what it saw but that part I think can be figured out by looking at the codes.

Basically, when coming to a stop leaving the car in drive mode once you get down to like 15 mph(ballpark don't know exact) it feels like the trans grabs and lugs the motor down and then it lets go and then grabs again and lets go and then the car comes to a stop. I don't have the exact spec on the cam, but its nothing too insane.

So, is this something with the convertor (I've been told its a little tight and an adjustment can fix this) or is this something in the torque management, etc? I had the convertor in the car before I had the cam and it did fine.

I'm not looking to set the world on fire at the track I'd just like to have the driveability without the car doing this everytime I go to stop at a traffic light...

Any help would be appreciated.

I've encountered the same problems or issues in cams. Well until now I can't fix it. Hope that there is someone who can help us. :D

[GeoffA]

http://forum.grrrr8.net/showthread.php?t=18350&p=285026#post285026

If your rpm's surge try this out, HPT...

[Executor999]

Next, make sure Torque Management, closed throttle downshifts (D9402) is set to NO.

This is what fixed the same problem in my car, thanks to Patrick G.

[OZPower]

No word yet. Hope to hear something by the end of this week.

[G8V8]

When you come to a stop, the rpm's surge and try to push the car through the brakes. excess pedal pressure is required to stop the car. Those who has this issue should be putting it in neutral as they coast until they get the tune resolved. No sense in bumping someones bumper.

I find that if I'm in manual mode and downshift to 2nd gear at 20-25mph (somewhere near there) and am not braking real fast, that the push is pretty much gone. I slightly feel something but the rpm jump and car lunging forward doesn't happen. In Drive or Sport is sure does.

[OZPower]

I find that if I'm in manual mode and downshift to 2nd gear at 20-25mph (somewhere near there) and am not braking real fast, that the push is pretty much gone. I slightly feel something but the rpm jump and car lunging forward doesn't happen. In Drive or Sport is sure does.

Right before I sent my car back I took it out for a little experiment. When I put it in manual mode and just came to a stop in second gear I didn't have any issues whatsoever stopping or feeling any jerking. Its just in the drive/sport modes so that's why its just something in the tune that needs to be changed and obviously Patrick has a setting that he recommends to turn off to fix that problem, but I haven't heard if the shop has tried or messed with that issue yet.

Last I heard was last Wednesday they found out there was a MAP MAF Correlation code that caused the car to go into limp mode so there are some tables that needed to have values maxed out to likely take care of that issue.

They were supposed to drive the car yesterday or today so that's why I'm hoping to hear something.

[G8V8]

Sounds like we have the same problem. good luck and here is hoping it is completely corrected. It means there is hope for me.

[OZPower]

Had a quick chat with my tuner last night and hoping to get my car back soon but some progress has been made apparently. He has to fix the reason why it went into "limp mode" first, which was maxing out values in some tables.

Since then he's been picking away at the transmission. He said the Closed TPS torque management setting seemed to help it from the RPM's jumping around if I understood him correctly as before the car fluctuated badly bouncing around right before the car stopped. He also said its around 5 mph where the car makes a 2-1 downshift and so he moved that to 1 mph and said its almost unnoticeable now, but was going to try and drive it again today and see if there was anything else he could do.

Has anyone else done this and/or anything else to correct it?

[OZPower]

I am wayyyy to late at responding to this thread, but the problem is fixed with special thanks to Patrick G. Two months of failure were finally turned around by this man. The downshift so it won't want to throw me into the steering wheel anymore and my surging issues were resolved thru tweaking some other parameters that I am not savy enough to speak about. The car was COMPLETELY different from when I first picked it up. So, if you have the same problem and are giving up hope...that man has the solution!