whats this valve by airbox for?

[jayeastanglia]

http://i1140.photobucket.com/albums/n563/jaycroker2/fb2f8873.jpg

Whats this valve for as both pipes have been disconnected..wonder if its connected with my slight flat spot at 1500rpm
its fitted to the side of the airbox by the distributer cap.

[Yosser]

I'm not familiar with 850's (the s/v70 is a little different), but I'm pretty sute thats the boost control valve, and you need to get that sorted out asap!!

[bigrotch]

Hi it's the boost control.... As it's got the vac lines disconnected you must have a manual boost control. Leave the electrical conection connected as i think it will throw up a alarm on dash I think.. I've got a manual
Boost controller and the vac lines are taken off the bc and connected to it same as the photo, so long as u got a NBC under the Bonnet then it's allgood

[JT]

yea, its the bcv, quite important that! lol

[jayeastanglia]

yeah it has a manual boost control valve under bonnet..dont seem to go to far up the boost gauge in the car..I am fitting a proper boost gauge in the car to check what boost its actually running so at the moment i havent adjusted the manual boost control valve..
goes about halfway up the standard boost gauge btw.

[bigrotch]

I know on standad Ecu with NBC u can boost up to 15 psi but it will hit the fuel cut on the Ecu, it's a safety thing. That is basically just off the end of the dash boost gauge, if you are only boosting halfway up I'd say either vac lines are perished..... Possible I've not quite running right when it's running pull out dip stick and if u see smoke yr Pcv system needs doin, mine wasnt running rite holding back etc tick over a little lumpy. It's a must do mate

[jayeastanglia]

no smoke from exhaust or dipstick tube as read about pcv can block up so cleaned that when i serviced the car as well as fixing a oil leak i had from turbo drain pipe..I have checked all the vac pipes and they seem ok even the multi pipe bit on the front of the engine as i know the blanks can perish and leak but the pipes all seem pretty new.I may even for now connect the vac pipes back to the standard boost control valve and see what happens as it may just be the manual controller isnt set up correctly

[cherry1809]

Also, Make sure your MBC is an MBC and not a bleed valve. Bleed valve won't work.

[bigrotch]

yeh give it a try,ive got a forge unos mbc and its the mutts nuts no spikeing very good boost control no silly big drops i boost,very smooth worthy investment.... ive got a cheaper mbc which is only a month old u are more than welcome to borrow it to try if ya want and as cherry said

[jayeastanglia]

I do still have a mbc from a escort rs turbo i used to have..but will try reconnecting up the standard one for now and if it dont work will try the mbc i have from the rs turbo

[bigrotch]

cool let us know how u get on mate