Technical Question on ASC (Acceleration Skid Control)

[drift838]

Hi,

I am experiencing some form of vibrations or shuddering from the back upon hard acceleration (car is a 318Ci valvetronic, done 50k km). The vibrations and shuddering is not rpm related, i.e. if I rev up slow to 6,000rpm, no prob, but if at about 30km/h, floor and kick down rev to 6000rpm the vibrations and shuddering occurs occasionally.

I was under the impression that it is probably due to some worn out bushings from the rear. But because I had the following replaced:
1. new automatic tranmission, transmission mounts (at 43k km)
2. prop shaft and final drive + related bushings (at 20k km)
3. improved BMW flex disc (at 50k km)
I am thinking that the vibrations and shuddering are not related to worn out parts.

It was after one of passengers mentioned that it could be possible skidding of the rear tires upon hard acceleration. My initial thots are that my car (143bhp, 200Nm) is not powerful enough to break traction on my Re050A Potenzas (225/45/17) at 32PSI. Furthermore, if there is traction loss, wouldn't my ASC kick in, but it didn't.

Can I ask that would ASC necessarily kick in when the rear tires break traction or does it depend on the severity skid. The reason for my asking is that this vibrations and shuddering tend to not appear when the roads are dry i.e. more traction.

Can anyone help me please. Please help me understand how ASC works.

Thanks

 

[chickenbackside]

Re: Technical Question on ASC (Acceleration Skid Control)

I can only comment on user experence.

From my experience, ASC does kick in just a fraction of a second after the tyres break traction. A very distinct power cut occurs when it happens. It's like your engine doesn't wanna rev. Also, some shuddering occurs.

But whenever ASC kicks in, one thing always happens: the ASC light will flash. So if you notice it flash, it means your ASC is working. If it doesn't, it means ASC was not triggered.

Yes, the ASC lights up all the time on wet days. On dry days, it lights up usually when you overcook a corner or when there's a sharp bump that makes your car jump a bit and lose traction for a little while while your foot is on the gas pedal...

Technically, I'm an idiot, so sorry I can't help you there.

 

[centurion]

Re: Technical Question on ASC (Acceleration Skid Control)

Check engine mountings.

0-6000 no shuddering since ECU limits torque.

30kmh to 6000, shuddering as engine is stressed, leans on mount.

50K km is high time you check the mounts. They are hydraulic (a-la Honda) if I remember correctly.

Hi,

I am experiencing some form of vibrations or shuddering from the back upon hard acceleration (car is a 318Ci valvetronic, done 50k km). The vibrations and shuddering is not rpm related, i.e. if I rev up slow to 6,000rpm, no prob, but if at about 30km/h, floor and kick down rev to 6000rpm the vibrations and shuddering occurs occasionally.

I was under the impression that it is probably due to some worn out bushings from the rear. But because I had the following replaced:
1. new automatic tranmission, transmission mounts (at 43k km)
2. prop shaft and final drive + related bushings (at 20k km)
3. improved BMW flex disc (at 50k km)
I am thinking that the vibrations and shuddering are not related to worn out parts.

It was after one of passengers mentioned that it could be possible skidding of the rear tires upon hard acceleration. My initial thots are that my car (143bhp, 200Nm) is not powerful enough to break traction on my Re050A Potenzas (225/45/17) at 32PSI. Furthermore, if there is traction loss, wouldn't my ASC kick in, but it didn't.

Can I ask that would ASC necessarily kick in when the rear tires break traction or does it depend on the severity skid. The reason for my asking is that this vibrations and shuddering tend to not appear when the roads are dry i.e. more traction.

Can anyone help me please. Please help me understand how ASC works.

Thanks

 

[shaaz]

Re: Technical Question on ASC (Acceleration Skid Control)

As long as the ASC/DSC finds loss of grip, any kind.. it'll be activated. the ASC/DSC light will flash, as long as it does not light up then i wld safely say that its not your ASC giving you the problem, sounds to me... sounds only la uh.. final drive, it could be ... anyways.. what i suggest you do is bring back the car to PML since you got everything done there and get em to hook the dignostics test kit to see if any fault codes are up. Then explain to them abt the prob and get em to check the undercarriage or the final drive for any loose parts .

 

[drift838]

Re: Technical Question on ASC (Acceleration Skid Control)

Thanks to all for advice.

Engine mounts were replaced at 50k km. I will have the car lifted up to have the rear mountings checked, esp the 3 rubber mounts for the final drive. Hope the 4 sub-frame bushings are ok as it'll be a big job to have them changed. But for a car that is never tracked, 50k km for subframe bushing wear seems premature. Sadly, visual inspection usually dun tell much

May I ask:
1. what's the normal life span of the rear trailing arm bushings?
2. what is the chracteristics of a prop-shaft that is out of balance?

Thanks again for any advice.

Regards

 

[centurion]

Re: Technical Question on ASC (Acceleration Skid Control)

1) I don't know. You'd have to get your computer to download the service manual for an answer to that. I only know VISUAL inspection required, I have never seen estimates before in the normal manuals.

2) Characteristic of a out of balance prop shaft - seems that it will vibrate badly at any gear, the frequency and amplitude of the vibration depending exclusively on your speed. Anyway, I have never seen any modern prop shaft being out of balance, thought this type of thing was impossible.