Bucking under relatively light acceleration... motor mounts??

[GregMB]

I don't know if it's just really lazy transmission adaptations or maybe bad motor mounts or ??? If I leave from a stop at perhaps 1/3 throttle (firm pressure but not aggressive) I usually get a strong "harmonic" bucking from the car as I try to accelerate.... almost like someone is jerking the throttle cable open and closed 3 - 4 times per second. If I drive super slowly, I don't get this effect and if I accelerate aggressively I don't either. Unfortunately, it's only when I try to drive like a "normal" person that the car ends up bucking and making me look like I don't know how to drive.... This may all clean itself up with a proper ECU tune (seems like EC and others make some changes to throttle sensitivity as part of even a "box" tune). Just curious if anyone else experienced this and found an obvious culprit. I've only got 34,400 miles on the clock now... no leaks on the driveway (aren't motor mounts fluid filled?), though there may not be enough fluid to confirm it that way. -G

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[shardul]

Transmission slipping?

[GregMB]

Originally Posted by shardul

Transmission slipping?

No idea....

Seems odd with such low mileage and being 100% stock.

I did bring it in at 32,000 for what I remember as a "Service D" (Brake Flush, Transmission Fluid change, Engine Oil change, etc). Just the standard stuff the dealership recommends at that interval.

Any "tricks" I can use to confirm a slipping transmission? I know on a manual gearbox you can accelerate through 1st briskly... then shift into 3rd or 4th to see if the clutch will bog the motor (good clutch) or if the revs will climb quickly (bad clutch....and smell usually too )

Could it be something like a bad transmission mount? Rear suspension bushings seem like more of a longshot since I'm not really accelerating too hard when it happens.


-G

[shardul]

Try doing a ECU / TCU reset and see if the solves the problem.

[moosejaw]

This happens to me too
from what when i asked a few years back this is normal for the car (stock or tuned)

[GregMB]

Originally Posted by moosejaw

This happens to me too
from what when i asked a few years back this is normal for the car (stock or tuned)

So..... I should stop being such a pansy and just mash the gas harder?

Guess I could try that. LOL


-G

[Kickem]

Mine did this when I first bought it with 60k miles and bone stock. First thing I did was take it to the dealer and had them check it out. They said that they could not feel anything unusual but the trans service was due so went ahead and had that done. When I got it back it still had the same bucking issue. I've done a few mods to it now (pulley, headers, full exhaust) and either I just drive it differently or somewhere along the line the culprit was addressed because it has gone away completely. I don't think there is anything "wrong" with your car, it's probably just how some of them are...

[GregMB]

You guys are probably right.

I've done the sneaky resets a few times in the past and the car always seems to wake up and drive better, even under part throttle it's easier to drive smoothly around town.

The problem is that most of the time I only drive on surface streets so all of my shift "history" ends up being really gentle driving. When I actually want to drive a bit more aggressively, the car just seems to shift strangely on the 1-2 shift and gives me that odd oscillating feeling.

I wish there was a way to flush the adaptive shifting "cache" every time I restarted the car. Realistically, I should probably just put the transmission in "C" (Comfort) mode. Maybe trying to drive too gently in "S" (Sport) is part of the issue?


-G

[Das Geld 2]

Try a quad tap on the throttle and car will buck so bad your face will fall off..its the adaptive ecu. Either push slowly or mash it.

Motor mounts you would feel something loose in the hood.

[03'55AMG]

I get this aswell. I find it best just to accelerate harder and to avoid it while slowing down, I give it gas then go straight to brake, because it only happens when i let it idle. The problem vanishes completely for me when the car is in Manual though

[GT-ER]

I opened a thread on this as well a while back... apparently is normal.

[Manuyc]

Originally Posted by GregMB

So..... I should stop being such a pansy and just mash the gas harder?

Guess I could try that. LOL


-G

[GregMB]

Did the sneaky ECU reset last night.

To confirm, here is the procedure as I understand it:

1. Get in car, shut all doors. Radio off, AC off, etc. (not sure if that stuff matters or not but I keep the process as simplified as possible)

2. Key into ignition (Position 0), past Postition 1 (center gauge illuminated) all the way to Position 2 (center gauge and all cluster warning lights illuminated)

3. Push and hold throttle all the way down to the floor for at least 5 seconds

4. While still holding the throttle all the way down, turn key back to Position 0 (all gauge lights off).

5. Release throttle pedal and sit motionless like a stone statue and watch the dash clock for the longest two minutes ever. Resist the temptation to open the doors, turn on the radio. Check email on my phone to kill time...

6. Remove key from ignition....put keys in pocket and restart car using Keyless Go.

7. Drive as normal, try to notice a major improvement in shift quality.




-G

[skratch77]

greg can you get into more detail about it?

the tcu reset for me just lets the Traction control system re adapt and lets the car break the tires loose easily and then after a few days learns how much power it needs to limit before it cuts in and after a while its near impossible to even do a burn out.

are you near windham? we can meet up and maybe show me in person

[GregMB]

Angelo,

What details did I leave out? The car is a low-mileage 100% stock E55... I drive around in "S" mode for the transmission and "C" mode for the Airmatic. CLS (18") wheels with 275s out back (Michelin PSS)..... Sirius radio is typcially set to "Octane"




I'm over in Keene. Not really a very quick trip to get together, but next time I'm in Manchester for service I could probably head down your way to say hello.

-G

[stevebez]

S/C Clutch engaging / disengaging / slipping?

[theblckghst]

greg i have the same issue too, I have attributed it to the larger pulley (185mm) because when it first started happening I figured it to be the motor mounts. So, changed them, one broken (driver side) one not. Same problem happening....light acceleration no jerk, heavy acceleration no jerk, regular acceleration big jerk. and it happens at the same rpm range every time, I think its just the SC turning on.