Just to update this thread for anyone thinking of doing this mod,
I've copied below what I've just posted in another thread regarding this mod now my car's been Decatted and Remapped. Honestly I think this mod is a must really for anyone considering doing the same if they have either a non operational exhaust valve in the way I had, or have done the Golf Tee Mod. Well at least if you like you neighbours!
When it comes to the exhaust I'm so glad I went to effort of fitting the switch to control it. You may recall from my thread about it at the time that when I bought my car the valve was permanently open which I thought at first might be a coding thing but I later came around to thinking based on the sheer number of other 2.0T E89's reporting the same thing thats is probably a common fault with the ECU controlled earth for the system. Whether its a wiring issue, an issue with the ECU itself, or even something as silly as an unintended consequence of a BMW software update I've no idea. What I do know is the net result was the same as the "Golf Tee Mod".
With the valve open on a cold start the combination of the air pump, the decat and remap are way too much. To be honest it was too much pre the mods with just the air pump, but the mods have significantly amplified this. Once your past those first few minutes of running its fine and I do quite like the added growl it has with the valve open at low revs/speeds that you don't get from the factory, but I'm also glad the switch is there, as at times I tire of it and appreciate something a bit more sedate. I was on Anglesey yesterday, there's some nice A and B roads on the island. I had a number of places to be that meant I had a day where I was driving all over the place, all top down and depending on how I was feeling dictated which "mode" I had the exhaust in. What I did notice whilst doing this is the valve position doesn't really seem to impact performance, the engine pulled equally as strongly with the valve closed and open, although I did only take it upto circa 4,500 rpm with it closed, maybe I would have noticed the performance being hampered if I'd redlined it but honestly I think the cat itself was a much much bigger restriction in the exhaust than the backbox valve. I'm increasingly convinced that BMW put it there purely to control noise levels and it has no real bearing on performance.
The journey from Manchester to Anglesey is roughly 100 miles, which is all Motorway and Dual Carriageway. Cruising along at the sort of speeds you do on these types of road and there's still no discernible difference between having the valve always open and always closed. To be honest this does surprise me a bit. Knowing what I know now if I were for some reason to buy another E89 with a working exhaust valve I'd still be tempted to re-wire it through a switch. Only this time I go for three modes. Always closed, as BMW intended and always open. Kind of like a COMFORT, NORMAL & SPORT mode.
