Alright lads and lasses, been searching through post upon post about this yo yo problem, my 2002 MCS is doing this and its driving me mad it feels as if its always holding back with a surging feeling when going up the rev range, ive heard the lack of power could well be down to the bypass valve so im going to check that but the yo yo problem still doesnt seem to havebeen answered by anyone?? people have reported that a software upgrade may cure this??? anyone got any ideas? and will BMW upgrade my software to the latest version for free:puzzled: or am i barking up the wrong tree? any help or sugestions very welcome, cheers.

Do you know the service history for the car? If it's been regularly been serviced by a dealer the software has probably been updated. A dealer is probably going to charge you for even checking the software version.

Hi ya

Good place to start is the bypass valve If you going to pull it out do the mod to it as well do a search here at mini2 you will find it. when it's out check the return spring they have Habit of breaking causing you symptoms loose of power and yo yo
But could be a software problem but it will have to go to the stealer for that and will most probably cost you about £130 ish
If you can do the bypass valve your self it's a good place to start because it's Free
if the spring is shot People like gt tuning do a modified bypass valve I think better spring and correctly set up if you need one give Roland a ring at gt tuning

Thanks for the info ill pull the bypass valve off this weekend.:)

Hi Pete_Cooper_S,

I've got an 02 MCS too and I've been living with the YoYo symptoms (as you describe) since I got the car about 4 years ago?

I heard that the earlier BPV had a weak spring which contributed to the problem so I've replaced it with a new one with no difference in symptoms.

I have a boost gauge (connected to the hose going to the fuel regulator and I can see the needle fluctuate. I'm not sure if the pressure is dropping as a result of the YoYo or the pressure fluctuations are causing the YoYo.

Next thing to try is the fuel regulator.


Cheers,

Dave