hi all , on the way home today my car wouldnt boost past 0.3 bar . I pulled over and turned the engine of and back on and i had full boost again .

Also before i got my VRS re-mapped the boost use to say around 0.5 bar , now ive got her re-mapped ive notice when in 2nd and foot down it stays at 0.75 bar , 3rd the same , 4th 0.8bar and 5th 1 bar . just woundering why ?

am i think its the N75 valve not holding pressure ?

It should hit peak boost regardless of what gear you're in then knock back a little bit and hold it there for 2000 revs or so before the wastegate opens fully and the turbo stops producing any more boost.

On a standard VRS the peak is about 10psi (0.7 bar) although mine hits 11 sometimes

On a remapped one it usually peaks a bit higher then settles down then fades so e.g. on my mates one with a generic remap it peaks at 18psi (1.3 bar) for a moment then settles down to 15psi (1.1 bar) then drops off as the revs rise further.

Something definately sounds a bit dodgy with yours. Possibly remap or N75 valve not controlling the wastegate correctly, or if you have an aftermarket DV is the spring setting too weak? Are you getting any error codes suggesting a boost leak anywhere?

Edited 23 March, 201016 yr by chicken_eyebrow

Ive always wanted to change the N75 , think it be a trip to skoda to price on up .

I dont think it will be the re-map as it was doing it before i had it done . Ive had no error codes before the re-map . Ive got the OME diverter valve .

What do the N75 retail at ?

Might be the OEM divertor valve is on it's way out - most remappers suggest changing it or include an upgrade to a Forge one as part of the remap package.

If you have a member near you with VAG-Com you could ask them if they will come out with you and do a few boost logs, otherwise you could get it rolling roaded and ask for a boost plot.

If it was only boosting to 0.5 bar before the remap then something possibly wasn't right back then, a VRS engine with a K03S turbo should peak at 0.7 bar, the 150bhp 1.8T's are the ones that peak at 0.5 bar.

Here's an N75 J valve, they're not too expensive:

http://cgi.ebay.co.uk/WGFV-N75-Valve-J-Version-Genuine-VW-Audi-Part_W0QQitemZ250592854744QQcmdZViewItemQQptZUK_CarsParts_Vehicles_CarParts_SM?hash=item3a587f82d8

Edited 23 March, 201016 yr by chicken_eyebrow

hi all , on the way home today my car wouldnt boost past 0.3 bar . I pulled over and turned the engine of and back on and i had full boost again .

Also before i got my VRS re-mapped the boost use to say around 0.5 bar , now ive got her re-mapped ive notice when in 2nd and foot down it stays at 0.75 bar , 3rd the same , 4th 0.8bar and 5th 1 bar . just woundering why ?

am i think its the N75 valve not holding pressure ?

It went into limp mode on your way home. Probably the result of a 17705 error code, but get it scanned to be sure. Could be many things, including dirty throttle, leaking hoses/valves etc. Plenty of info floating about, and I'd say probably 90% of 1.8T's get this problem at some point!

Your boost question is hard to answer without knowing more about how you were driving at the time. The boost is related to engine load (no load means no boost), that's why you don't hit any boost in 1st gear, as there's no load. Are you loading up the engine properly in each gear when you're doing your boost check? Peak boost should be measured while in 3rd gear, hold the car at 2000rpm, then go WOT until 3000rpm.

The engine can be mapped to run different peak boost in different gears, since the ECU can calculate what gear you're in from engine speed and road speed. But I've not heard of anyone doing generic maps like this before. That's the only way I can think that you can really get different boost in different gears, under full load.

Bit of an odd one! You really need the error codes reading first.

Ive had the 17705 code before and cured it so im really hoping it wont be that . It does seem abit hesitant after the re-map though , but ive read other people have this problem to . Ill try and see this weekend if i can get her read on a VAG.com and keep everyone posted .