instability at speed

Toe-side said:
gonads said:
As I mentioned initially, I've had a full alignment done and the car has been thoroughly checked over, the poly bushes improved turn in dramatically, the car handles well, predictably and evenly left and right. Runs true and is enjoyable apart from this oscillation. It seems as though the steering is over reacting to input from the road wheels at certain speeds, possibly some sort of aero/loading combination. In the absence of any other ideas the only thing I can think of is to start replacing the front suspension components progressively.
Click to expand...

I have been trying to diagnose this problem for a few months. I would agree its as if the the power steering is assisting to much at a point when its not required. Its most pronounced at the speed you are experiencing on mine not experienced at lower speeds.
I have posted outputs (video) from the steering angle sensor (no replies) I thought it was a wheel speed sensor but that fault has not been initiating on the reader. It is intermittent in nature but when it starts it really degrades the driving experience :cry:
All suspension is ok....... its definetly the power steering input for me
Click to expand...

Its not the wheel balance, suspension, bushes, paint on the rims, alignment, RFT's, tram lining...... for me its feels like the intermittent assist of the power steering. Like some one else is trying to turn the wheel for you a little, back and forward. Jump in the car some days and no issues, even on the same roads.
 
Toe-side said:
Toe-side said:
gonads said:
As I mentioned initially, I've had a full alignment done and the car has been thoroughly checked over, the poly bushes improved turn in dramatically, the car handles well, predictably and evenly left and right. Runs true and is enjoyable apart from this oscillation. It seems as though the steering is over reacting to input from the road wheels at certain speeds, possibly some sort of aero/loading combination. In the absence of any other ideas the only thing I can think of is to start replacing the front suspension components progressively.
Click to expand...

I have been trying to diagnose this problem for a few months. I would agree its as if the the power steering is assisting to much at a point when its not required. Its most pronounced at the speed you are experiencing on mine not experienced at lower speeds.
I have posted outputs (video) from the steering angle sensor (no replies) I thought it was a wheel speed sensor but that fault has not been initiating on the reader. It is intermittent in nature but when it starts it really degrades the driving experience :cry:
All suspension is ok....... its definetly the power steering input for me
Click to expand...

Its not the wheel balance, suspension, bushes, paint on the rims, alignment, RFT's, tram lining...... for me its feels like the intermittent assist of the power steering. Like some one else is trying to turn the wheel for you a little, back and forward. Jump in the car some days and no issues, even on the same roads.
Click to expand...


Agreed, I had it again this morning on a road I had previously thought I was no longer getting the wheel movement. And this was with the sport mode enabled which I also seemed to believe was easing the issue, but clearly not.

It does seem to me that it's something created by the electronic power steering in some way.

edit: Possible route cause of problem below, over compensating ???

The intelligent assistant.
Electric power steering on the BMW Z4 Roadster.
The BMW Z4 Roadster's electromechanical power steering makes for an even more dynamic drive. A torque sensor assesses steering input and adjusts the steering to the driving situation, resulting in a more direct feel. For even greater steering feel, just press the "Sport" button. Activating sport mode reduces the level of assistance, enhancing the driving experience yet further.

http://www.bmw.com/com/en/newvehicles/z4/roadster/2006/allfacts/engine_eps.html
 
Toe-side said:
Toe-side said:
gonads said:
As I mentioned initially, I've had a full alignment done and the car has been thoroughly checked over, the poly bushes improved turn in dramatically, the car handles well, predictably and evenly left and right. Runs true and is enjoyable apart from this oscillation. It seems as though the steering is over reacting to input from the road wheels at certain speeds, possibly some sort of aero/loading combination. In the absence of any other ideas the only thing I can think of is to start replacing the front suspension components progressively.
Click to expand...

I have been trying to diagnose this problem for a few months. I would agree its as if the the power steering is assisting to much at a point when its not required. Its most pronounced at the speed you are experiencing on mine not experienced at lower speeds.
I have posted outputs (video) from the steering angle sensor (no replies) I thought it was a wheel speed sensor but that fault has not been initiating on the reader. It is intermittent in nature but when it starts it really degrades the driving experience :cry:
All suspension is ok....... its definetly the power steering input for me
Click to expand...

Its not the wheel balance, suspension, bushes, paint on the rims, alignment, RFT's, tram lining...... for me its feels like the intermittent assist of the power steering. Like some one else is trying to turn the wheel for you a little, back and forward. Jump in the car some days and no issues, even on the same roads.
Click to expand...

Hi,

The power assist servo motor should only provide assistance when torque is applied (By the driver) to the steering wheel, the amount of assistance being calculated depending on the the variables of speed, steering angle etc etc. Obviously, when no steering input is applied , no assistance should occur.
The only way to prove this is or is not a power steering issue is to pull the main power plug to the rack (Bearing in mind the steering will be bloody heavy at low speed) and try the same speed run again - At least you will have a positive answer one way or another.

Stu.
 
Apparently pulling fuse 22 disables the low speed power assist to the power steering and gives a heavier steering without killing the motor totally.

http://www.bimmerforums.com/forum/showthread.php?1924534-Remove-Disable-Power-Steering

I'm going to give this a try before i drive home from work and see if that has any effect.
 
Thats good input I will have a go at disabling the PS either by fuses or power plug. :thumbsup:
I am thinking its the steering angle sensor signal but its not leaving a fault code.
 
panderoo said:
Apparently pulling fuse 22 disables the low speed power assist to the power steering and gives a heavier steering without killing the motor totally.

http://www.bimmerforums.com/forum/showthread.php?1924534-Remove-Disable-Power-Steering

I'm going to give this a try before i drive home from work and see if that has any effect.
Click to expand...

Right. Tomorrow morning fuse 22 is coming out. Watch this space.
 
gonads said:
panderoo said:
Apparently pulling fuse 22 disables the low speed power assist to the power steering and gives a heavier steering without killing the motor totally.

http://www.bimmerforums.com/forum/showthread.php?1924534-Remove-Disable-Power-Steering

I'm going to give this a try before i drive home from work and see if that has any effect.
Click to expand...

Right. Tomorrow morning fuse 22 is coming out. Watch this space.
Click to expand...

+1 :)
 
I flipped the fuse out this morning for my drive to work and as a word of warning for anyone else, it certainly makes the steering quite a bit heavier.

On a plus side the steering felt much more stable in a straight line with no unwanted steering movement what so ever, although I'm not certain if that points to anything at fault with the EPS or if it was just so damn stiff with it disconnected that it physically couldn't oscillate.

Also with Fuse 22 removed the aircon no longer works so it steamed up pretty quickly in the rain.

The below makes interesting reading if anyone is feeling brave:

http://www.autospeed.com/cms/article.html?&A=111532
 
Spooky
I was just going to post a similar story on mine. Its is something to do with EPS for my money as the car was planted at speed with Fuse 22 removed. Stopped and did the same drive with EPS back in service and the issue/gremlin returned.
The steering is pretty awful at low speed without EPS and yes my aircon didn't work either! Very strange that the Aircon takes the same supply?

I am going to replace the steering angle sensor (not a job that I have done before) to see if that is the issue or does anyone know to reset or adjust/calibrate the steering angle sensor?? As stated before its not sending out a fault code.
 
silly question; where is the fuse box? tempted to try this tomorrow moring, if it's not raining so I don't fog up :P
 
Ed Doe said:
silly question; where is the fuse box? tempted to try this tomorrow moring, if it's not raining so I don't fog up :P
Click to expand...

Fuse box is behind the Glove box -
Open glove box
Release the glove box damper
Push in the two clips that stop the glove box flopping totally down and the fuse board is behind once it has flopped down.
 
Toe-side said:
Spooky
I was just going to post a similar story on mine. Its is something to do with EPS for my money as the car was planted at speed with Fuse 22 removed. Stopped and did the same drive with EPS back in service and the issue/gremlin returned.
The steering is pretty awful at low speed without EPS and yes my aircon didn't work either! Very strange that the Aircon takes the same supply?

I am going to replace the steering angle sensor (not a job that I have done before) to see if that is the issue or does anyone know to reset or adjust/calibrate the steering angle sensor?? As stated before its not sending out a fault code.
Click to expand...


Another interesting read http://www.mgf.ultimatemg.com/group2/common_problems/epas_reset/

I have no idea if our EPS works in the same way on the z4, but i might jack up the front of the car and see if the front wheels turn themselves.

I suspect that it's the steering angle sensor or the torque sensor that's doing funny things and causing movement.


Let us know if you replace the angle sensor and what the results are.
 
Another good link from a previous post as well. http://api.viglink.com/api/click?format=go&jsonp=vglnk_14160843645839&drKey=1439&libId=424e532e-9818-449b-ab04-52bf37a0cc1f&loc=http%3A%2F%2Fwww.z4-forum.com%2Fforum%2Fviewtopic.php%3Ff%3D3%26t%3D40178&v=1&out=http%3A%2F%2Fwww.bmwclub.lv%2Ffiles%2F06_E85_Chassis_Dynamics.001.pdf&ref=https%3A%2F%2Fwww.google.co.uk%2F&title=Z4-forum.com%20%E2%80%A2%20View%20topic%20-%20help!%20Random%20Power%20Steering&txt=http%3A%2F%2Fwww.bmwclub.lv%2Ffiles%2F06_E85_Chas%20...%20cs.001.pdf
To replace the steering angle sensor looks like a steering column out :cry:

From the link thinking it might be the torque sensor so will be looking at your link/post. Thanks :thumbsup:
 
No sorry events have overtaken me work, family and other projects. Not enough time to investigate further at present.
Its still driving me nuts when I am driving.
This was the video I up loaded on the steering angle output but no one could identify whether this was normal or not. Doesn't look right to me.

https://www.youtube.com/watch?v=eFGNdQKGqPs
 
I had a new steering column fitted on mine a few years back under warranty when it was randomly sticky at certain speeds making it jerky to keep in a straight line. Sounds like a similar issue here though hopefully there are some cheaper fixes out there now. Was a fairly common issue for the earlier cars with 40k miles or so on them back then.
 
Just to update of this with what has pretty much cured my strange steering wheel movement.

Tyre pressures:

Front: 36psi
Rear: 30psi

I'm on normal non run flat tyres, they are about the cheapest nasty tyres possible (fitted by previous owner) and it has 95% cured the problem.

I'm sure you could run the rears with more pressure, but it was a lot smoother ride with 30psi.

Not sure if it will help anyone else, but it won't cost you a lot to try.
 
If you've recently had the alignment checked, can you post the results? Any amount of toe-out can produce lairy steering on public roads.
 
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