Help needed! not holding boost

[popdemonic]

Bumping

[popdemonic]

Mate,I seem facing kinda issue too on my UrS6.I'm thinking my BPV might be bad since

I was running the HKS SSQVII BOV and never had kinda problem before.My boost will be

fine what so ever when it's max not over 1.5 Bar.Firstly I tried to rule this out by getting

Greddy E-01 EBC on my car but It seems i missed the point bacause,the boost is still falling

off when i hit 1.8 Bar.Let's details the issue,it seems everytimes When I WOT the boost will

be max at 1.8-1.9Bar.During I keep my foot all the way down then the boost is falling off from

1.8Bar to 0.5-0.6Bar.Definitely,The car feels like it's pulling back.So when i let off and stumble

on the gas again.The boost will be max out 1.8 bar and do the same way.The reason of getting rid

of the N75 valve because I think it's the cause.I also ever gotten one good known of N75 but

it couldn't fix.I replaced the WG and finally I got zero on hope.So the best way to rule this out

is getting the Greddy E-01 EBC.But the issue is still there too.one thing I have been noticed is

with the 710N BPV I ever heard a little 'wooosh' sound when let off the gas to let us know that it's

performing their job.But now It's quiet.in stead,When partially let off the throttle sometimes I heard

kinda like the compressor surge.It's not that loud to be horror but enought to be noticed. I ever took

off the BPV and using the air mouth to do the pressure test.But I've realized that 1.8Bar on the GT2871

and my mouth is absolutely another story.Anyone ever has BPV leaky under high boost? I STFA I found

Paul or someone else said the 710N is good hold on the boost at 1.6bar.So I'm running 1.8 Bar.Maybe

the BPV is stick opened at exceeded of the boost level.I'll find the new BPV and have them try.will let

ya know Mates.

Cheers,

POP

all the way

[AndyP]

Did you ever get to the bottom of this?

[S2central.net]

Yeah - thats another thing - avoid unknown entities such as the VR6 MAF...

100% agreed with DKW that lambda probe is very likely cause of poor MPG - but that alone doesn't explain why its not boosting properly. It *may* be overfuelling because of unmetered air being drawn in under vacuum (cruise) - which would make things lean out except that ECU and lambda does the job of enrichening mixture to counteract the air that hasn't been measured on the way in.

This unmetered air under vacuum becomes a boost leak when the inlet manifold has positive pressure. Is the penny dropping yet ?

[dkw_dude]

If MPG is low and it runs badly I would check lambda sensor operation and replace if in doubt. MAF too, try one from a good running S2 .Tested with VR6 MAF, is this the same as the same as the S2 maf?

[S2central.net]

Lets go back to basics on this one.

Cylinder compression all OK ?

Spark plugs all correct and properly torqued down (no loose ones) ?

Rather than just replacing all the vac pipes you can see in the engine room - have you actually leak tested them from where they attach to the inlet manifold ? They should all be airtight... I had a leak at a checkvalve which was also hiding an integral joint that was linked to part of aircon controls.

As for leak tests - try to do one that doesn't blow air into MAF pipe - very unnatural to see pressure here of course... Setup so that you apply pressurised air to simulate boost coming out of the turbo - at the hose which connects to intercooler - and with the throttle body bunged up you should have a completely airtight system - this is only way to test integrity of hoses to/from intercooler & the intercooler itself.... Just saying you have done the MarkH mod does not protect you from a cracked intercooler... And when doing the leak test from MAF hose - the air could be escaping faster thru turbo oil seals than the intercooler so its a crap test.

You need to isolate things to reduce number of parameters and reduce complexity.

With VAGCOM - get a screenshot of Groups 0-1-2 whilst on a warm idle - that will help me see somethings and hopefully provoke questions.

I'm still thinking MAF or knock sensors - though I wouldn't discount TPS or Altitude sensor at this stage.

While we are testing sensors - get a mutimeter out and discover the following - at ambient temp of say 20 degress

Resistance of IAT
Resistance of CTS (coolant temp sensor at back of head - usually white plug)
Resistance of Altitude sensor
Voltage of TPS on pins 1-2-3 at WOT

[iib3327]

Try to pull off the hose to the WG but be careful now it will overboost, if u had a manually boost cntrl i would be easier to see. It sounds like wg bleeds somewhere , and you are totally sure the IC is ok ? see the little O-Ring sometimes pops.

What kind of gas are u driving on ? Super the motronic works best. 98 unleaded

And Spark plugs are OK ?

will try unpluging the wastegate thats something i havent tried...

i have the mark H mod on the intercooler as the 0-ring was shot to say the least..

have tried all sorts of fuel but no difference in them as im not seeing any kind of performance (all be it for 13-17mpg)

[chipsenter]

Try to pull off the hose to the WG but be careful now it will overboost, if u had a manually boost cntrl i would be easier to see. It sounds like wg bleeds somewhere , and you are totally sure the IC is ok ? see the little O-Ring sometimes pops.

What kind of gas are u driving on ? Super the motronic works best. 98 unleaded

And Spark plugs are OK ?

[iib3327]

eye Gav's right been to gti inters this weekend, didnt have the time to check the s2's timing sat either as was fitting TT seats in the misses polo..lol

have checked the timing today and all checks out fine. also found the TPS at only 92% so set that at 100% and guess what still not a lot of boost..

think i need to pass it onto AVP get them to give everything another look over as i can only hope its something i've missed now.

[gavs20v]

Think matts at gti international this weekend matey

[220bhp]

I guess you fixed it or got fed up and sold the car

[220bhp]

I cant seem to get the link, but type into Google Automotive tutorial Audi s2 and it should come up.

[220bhp]

I really can sympathize with you on this problem, but there is an answer you just have to keep looking. There are a couple of things that you may or may not of checked, on is timing and its related to the front cam sprocket, it has a key way which can fail if the crank bolt hasn't been tightened enough, this will allow the sprocket to put the timing of a couple of teeth, the car will still run OK because the ecu compensates for it,but it will not boost as it should, and you will get poor fuel consumption.
Again it maynot be your problem but it needs to be ruled out.

[iib3327]

problem is they said i've checked more than they would (also a lot more times than they would) and some things they seemed puzzeled that i've checked. so seems a waste to pay them to go over a few of the things i have..

all vacumes have been replaced (or platic hard lines checked and double checked)

paid to have the ecu full health checked

i think i've been more than patiant with it 3 months of owning a car i've always wanted to do 17.4mpg at its best and be slower than a mk4 golf gti thats doing 30+mpg.. seems a waste of time money and effort atm..

[max_s2]

I have the same problem, the boost is falling off to 0.8bar after receiving 1.1-1.2bar. Seems like overboost is holding only for max 0.5-1 sec.
BTW, no faults in ECU.