Help needed! not holding boost

[iib3327]

right im getting to my whits end with this problem..

when driving i see max boost of around 1 bar but it soon tails off to 0.4-0.5 bar and feels like the cars holding back. if u take your foot off then plant it again back to 1.0 bar car pulls really well then tails back off again to 0.4-0.5 bar.

so far i've.

fitted new reserc valve
swopped N75 (altho its a new on fitted)
car has had new turbo, wastegate, head rebuild, new ecu (all this just befor i had it)
have boot leak tested car
fitted mark H mod after found that leaking
replaced all vacume hoses
set mechanical boost at 0.4bar after finding it had been set much higher causing boost cut.
checked wiring to n75 all ok

so the burning question is now what the hell do i check next as i feel its beating me and i love the car just not this issue..


only thing i cant seem to get an answer on is why when checking for leaks the air bleeds off into the wastegate through the vacume and i dont know if this is normal?

any help would be awsome people..

Matt

[iib3327]

nobody ever boost leak tested thier s2 then? come on peeps

[Jamo]

Have you had the wastegate checked? could be the cap in the wastegate has split

I have a pressure testing bungs, you can use if you like but you need to use a air line from a compressor to fill it up with air.

[pixsaudisex2]

whats the switch under the water manifold the wtfs... or what ever it is the one with four or three pins. im sure when mine packed up it done stuff like this.

[Jamo]

I thought the MTFS only limited boost on the 3B cars?

[pixsaudisex2]

Certainly held mine up i was going to give up on the car and sal asked if i had changed that and ye har of i went smilling away.. So it limits something.. must be limp mode. but some times it worked and some times it didnt.

[Jamo]

Didn't know it did it on ABY, cheers for the heads up

[iib3327]

i have boost leak bungs cheers for the offer jamo, the wastegate is new had it apart the other day tho to check? but what should i be looking for to be split?

whats this sender under the water manifold all about? (MTFS) will change this no problem just need to know what to order..lol

cheers for the help guys..

Matt

[pixsaudisex2]

If i remember its under inlet manifold on water manifold if you search on here there is loads of info on it. you can dissconect it i think to see if it makes any difference.

[iib3327]

tried this and seemed no difference? i take it thats not the problem or does this mean it is the problem? lol im lost now
(easily confussed!)

[ericd]

tried this and seemed no difference? i take it thats not the problem or does this mean it is the problem? lol im lost now
(easily confussed!)

have you got access to vag-com or somebody who has ?, subsequently have you
ever reset the ecu errors or pulled the fuses after changing the various parts you listed ?

[prosty]

Get a stiffer wastegate spring to get higher base pressure, however the car SHOULD hold pressure anyway, but a spring is always good to FORCE the ******* into boost

I don't like the n75 setup and would recommend most ppl to use a mechanical controller instead of that thing. However with just a tuning chip with a stock turbo, then the n75 is OK.

If the wastegate leaks when you pressure test the car, then the membrane is probably screwed, try with a new WG.

[iib3327]

ericd i have vag com myself never brings any codes up in general. check the fueses time and time again too..

prosty the wastgate and n75 were new when i had the car, i have had the wastgate apart to see if i could see anything obvious? is the membrane the fabric style seal inside? might be worth me swopping this just in case as the wastgate was screwed right in when i had it (due to boost leak) so has been tampered with since fitting...

gives me something else to try tho cheers guys..

Matt

[newsh]

If the wastegate diaphagm is split you will get too much boost, not too little. The air you here leaking inside the WG is just going down the WG valve guide into the exhaust, totally normal.

I'd be looking at the knock sensors if its holding back.

Or you still have a leak somewhere... ... normally though, if its a leak you'll get the "\MAF Cutout" effect and the car will lurch badly.

Bad knock sensors do not always throw up a code.

[iib3327]

well just stripped the wastgate again for no reason then

newsh i was getting that lurching when i fixed my boost leaks as the wastgate screw was wound right in (set to 0.4 with n75 unplugged now and stopped it lurching)

not thought about nock sensors yet.. i take it its just buy new ones to rule that out also?

cheers again guys..