Any VAG experts??
 

I recently bought a 2007 2.0 A3 tdi from my brother as a run around with the added non bonus of a PO234 over boost fault when speed exceeds 60+mph. Now the overboost fault isn't my query it's something else but I thought I'd lay that down first.

When I first drove the car I thought it felt flat, having owned an A3 2.0 TDI previous, it didn't appear to feel as quick so I put it down to the turbo, or it's need for a new one. Whilst searching online for the PO234 fault I came across a YouTube video where by some guy was showing movement of the turbo actuator arm if the vac hose was removed from the vacuum reservoir.....In doing so, I snapped the nipple of the reservoir pulling a little hard! After that I shut the bonnet and hadn't driven it since.

Yesterday I needed to use the car and on doing so I noticed how much more responsive it was, it actually felt like my old one so today I blocked the vac hose with a bolt to see how it performed, it felt flat again so removed it, the difference is night and day. My first thought was that it was creating more boost so hooked up the Torque app and an OBD adaptor to measure the boost, it was making roughly 22psi with the bolt in or out but boost comes it much quicker with the vac hose venting.....I've looked online trying to find an answer but haven't really found it.....So can anyone tell me what the vacuum reservoir actually does and why it would make the car perform so much better without it inline.

over boost can be soot build up on the vanes of the turbo, causing them to stick,
a few products will clean them.

Yeah I know but overboost isn't my issue....It's that when the vac hose is removed from the vacuum reservoir (black ball) the car has more punch and doesn't feel flat like it does when connected.

Which engine?

2007 is the cross-over between common rail and PD.

PDs have a bunch of vacuum pipe for EGR and turbo with a box of voodoo on the bulkhead and accumulator sphere on the engine. It's a 10yr old car so plenty of brittle Bakelite-like plastic bits to break (been there :o ). With a leak in this system I'll probably assume that the EGR will stay closed (good!) and VNT on the turbo will be in its low speed position (better boost at low rpm, but limited top-end).

Lack of oomph is probably as mentioned..the VNT turbo or the actuator/N75 valve (built in to the voodoo box; used to be separate ). They are fickle, if the vanes/nozzles are not in the exact position the turbo doesn't behave. Usually they will take forever to build boost and then overboost once spooled, in the other positions it'll build boost quick but under boost overall and generally feel flat at higher rpms.

If it's the common rail engine, the early ones used to suffer leaking turbo actuators, this resulted in crap performance , but IIRC these had a sensor on the actuator so if this went faulty you'd get a charge/pressure deviation fault code.

So based on that I'm guessing you have. 16valve PD, probably a 140ps BKD.

Yes it's a PD 140 BKD with the vacuum block on the bulkhead. I actually changed the vacuum block because of the N75 but the overboost issue was still there(was hoping it was that rather than the turbo). My reason was that the actuator does appear to move it's full travel but I've now conceded it is the VNT sticking.

My post was more to do with the performance of the car with the vac hose disconnected from the vac res. It seemed strange that the car performed like you would expect it too disconnected. I plan to remove the turbo and either try and clean/free the vnt or replace for new, also remove the EGR and EGR cooler in the process...

You can clean them in situ with good results,
Ive used Innotec in the past, I did make a decent seal for the zorst, they supply a flimsy thing.

Man i had one of these BKD140's and it was nothing but trouble. Constant error codes and guzzled coolant even after a full EGR + cooler delete. My first overboost code i took to a professional and was diagnosed as EGR fault aka the bulkhead vacuum block - even after innotec cleaning the turbo it still overboosted randomly (ie 70mph cruising) yet pulled hard all the time. I had my own Vagcom so just kept topping the coolant up and clearing error codes until someone bought it off me cheap. Worst car iv ever had

Guy i worked with also had one, but an audi like yours..took it for a cambelt and one of the tensioner bolts snapped in the block - apparently common fault...cambelt turned into engine out jobby to fix it and cost about 6 times as much!

Moved to an E46 330d since then, wouldnt look back at 4pot VAG's now after having a straight 6 BMW. Maybe a good mapper can diag it for you when you get the ECL mapped out after blanking the EGR? Id get shut personally lol

I have seen that but with mixed reviews, people also using Mr Muscle foam. By removing the egr and egr cooler it gives me direct access to an entry in the exhaust manifold without removing the turbo intake pipe and squirting it in that way, so I'll see if that works before I remove it.

To be fair, the car was almost given to me in terms of price and even with an egr delete kit, new turbo and remap it would still owe me less than half of what they sell for so keeping it for a run around is a no brainer really...

No turbo intake pipe removed for the vanes fella, its the zorst side,
may explain why others have failed lol

Yeah sorry my mistake, its early.!

Removing the V-band and pulling the cat out of the way, it still has mixed reviews...

because the seal is poor, unless you do something about it . . .

This is why I tell you to make a better one, I used a but of old ply,
it stops the cleaning fluid from leaking out, thus staying in the right place cleaning as designed, doing what it should . . .

:thumb:

You basically need to fill the exhaust side with cleaner and hold it in there while you work the vnt system manually so it gets a good clean. The card template they supply isnt great and also mr muscle oven cleaner works just as well! Dont forget to clean it out afterwards though, think i just used brake cleaner then started it up for a few seconds with the downpipe still off

I am but not that kind .

???

He is implying that he is a vagician

Like Ron Jeremy & Rocco Siffredi ? lol

I don't know who those guys are but I am sure you are correct:D