coolraz

Hi guys,

I have this weird thing that seems to happen when I'm accelerating, the RPMs first increase, then stutter and go back down about 250rpms, then as I keep pushing down the throttle, it will accelerate again normally. The best example that I have is at 0:18 in this video, where I start accelerating, then it hesitates, and I did it several times. Now, this is NOT a gear-shifting type of hesitation that other people have with the 7AT, b/c its staying in the same gear the whole time.
BTW I have WOT restriction removed (with uprev ECU flash), but this is something that happened before the flash and still happens now.
It mostly happens between 40 and 70 mph, but that's possible because 90% of my driving is the commute on backcountry roads to work that is at those speeds.

Can you guys tell me if this is normal?

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mikelr

iTrader: (1)

If your engines RPM is actually changing and it's not just your tach then it has something to do with the transmission software. Looks like the apply clutches in what ever gear you are in are allowing slippage for whatever reason. These clutches apply holding pressure to corresponding clutch pack in the auto trans, they are controlled by electronic valves that are controlled by the ECU or whatever computer controls the shifting of the transmission.
I would imagine the only way to diagnose the issue would be to have the dealer do some diagnostics on the transmission or even some data logging during a road test to pin point the issue.

Frankyg37s

iTrader: (3)

doesnt look normal too me but i have a 6mt

coolraz

Mike,
Thanks for that insight. That actually made me think about the gears part so I just tested it out.
It's definitely NOT just the tach. The video has road noice, but I can definetely hear the engine rev slightly when the tach does.
In DS and D mode, it is VERY prounounced. In manual mode, I went through all the gears 3-7 and basically it happens almost all the time in 7 (it's less noticeable at 40mph and increases to where at 60mph it can easily jump up 1000rpms and back down 1000rpms before accelerating normally after), once in a while in 6 and virtually never in 5 and below. So it sounds like what you're saying is spot on, and it makes sense that 7th gear is the most prone to slipping.
Good thing I'm going back to dealer this week to replace a splash guard from which paint is peeling so they can take a look at this.
Thanks for the help! Anyone else ever has this kind of issue??? I though slipping should only happen if you get FI and gun it in 7th gear : )

ANMVQ

iTrader: (13)

No part of the slippage I think is from the torque converter locking up. This seems to be an issue
with all the 7 spd's. My wife's sedan does this all the time in 5 and up gears. But then again
I'm only doing 35 and in 5th. ... :/

coolraz

Hmm, I dunno, I thought that lock-up in torque converters was a feature that was added to reduce slippage. My understanding of modern auto tranny is that in the torque converter there is fluid but also an actual clutch plate, so that it's not just spinning the fluid but at certain times physically couples the tranny. From what mike is saying, it sounds like the lock-up is NOT working properly, thus allowing it to spin, then finally it locks up and then it accelerates normally. Lol i am def no mechanic so maybe that's all wrong.

This just bothers me a lot because on my daily commute it's extremely noticeable....so i'm actually hoping it's a defect in my car rather than just "what all 7at trannys do"

KevinM

I am having this same issue, has anyone come up with a solution, or found the cause? Please help as I've searched multiple forums and came up with nothing.

slartibartfast

iTrader: (7)

The torque converter doesn't lock until about 2,200 rpm when accelerating. It will stay locked when decelerating below that rpm until you hit the gas whereupon it unlocks as needed. It took me awhile to realize this after I bought the car. I'd accelerate modestly and engine rpms would hardly rise in the low 2k range until speed matched that necessary to allow the torque converter to lock. Then, rpm rose as expected.