S3 Performance loss..please Help.

squale

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Hello,

I would to expose a problem which i experience with my S3 as i am becoming desperated.

The car : 2002 225 S3, ABT remap, stainless steel catback exhaust, silicone induction hose, cotton panel air filter in standard airbox, which was running very fine until the following pb occured:

When I log the boost with VAG COM, It never reach the target boost: i.e: 2300 mbar instead of 2500mbar for example between 3000 rpm and 4000 rpm.

Moreover, I especially feel a strong loss of power of the car, especially in recovery, and what is strange it is on motorway in 6th gear for example, when I floor the gas pedal, the boost sometimes stagnate (i monitor with a gauge) and pass suddendly to full boost (1.3-1.4bar,but not to the requested 1.5 bar), this stagnation problem seems to disapear when unplugging the n249, but despite everything, the performance still remains poor.

Another phenomenon: sometimes when I release slightly the gas pedal , i feel the car pulling stronger..

I guess that all this must be dependent but I despair to find a solution now.

I replaced with new oem parts : dump valve (710N), the n249 and n75, as well as the suction pump (small Y of plastic) under the intake manifold (which was leaking oil). I also inspected all the hoses and connections I do not find any leak.

Thank you for your assistance.
 
Thank you !
I checked the maf, depending on external weather its between 180-196 g/s, i guess it should be ok. I tried with the MAF unplugged and no changes..
 
Does the car run fine apart from loss of boost, i had a similar problem and the n75 was plumbed in the wrong way round
 
Sounds like a boost leak only way to check is a pressure test I suppose. Could be hole in the intercoolers?
 
If you don't have any boost leak try unplugging completely N75, have a short run (one only!) and see what pressure you get on your boost gauge/Vag-com. Should be around 2600 mbar or more for a second. If it's not than it may be something wrong with your turbo, for example WG actuator stuck in one position..
 
Interesting, I used to get exactly the same problem on my Golf.

On the motorway, you could put your foot down at say 80-90 and it would literally 'stagnate' or rather not a lot would happen, it would obviously accelerate but not like it was on full boost, as if the TIP had collapsed (even though it was a solid metal item) then you could let off the gas slightly and all hell would break loose (full requested boost)...very weird.

I've experienced it a few times on the S3 as well, not the norm though.

Would be really interested to know what the cause is.
 
I think i definitely must do a boost leak check, whats the best way to check this ? btw i will try to unplug the n75 to see if turbo is pulling enough too..
 
Hi,

some news, I bypassed the N75 and the boost grew up to 1.6 bar, so i guess the wastegate is working ?
 
Yes your wastegate is working if you are getting 1.6 bar at the manifold.

So if there's plenty of air (and have - 1.6 bar of it) then the fuel and ignition sound more likely to be at fault....or the timings there-of....I am begining to wander whether yoru throttle body is going a bit icky. They are a pain as they don't always thow up a fault.
 
Does someone know how to check Fuel, Ignition & Timings with VAG COM ? Also i would to check the lambda ?
thx !!