Boost leak?

freezebox

Registered User
Hi,

I have a 2.0 TDI Quattro 170 A3 that has been remapped and DPF removed, EGR blanked. should be around the 215bhp mark. The remap (was) absolutely fantastic, it completely transformed the car, even a dab of throttle would shunt me forward and the torque was amazing, so good infact the clutch used to slip in 4th gear (replacing clutch in near future).

Recently however when giving it a bit of beans the car no longer feels as quick as it did, seems like theres not much boost there. The turbo was inspected when the DPF delete was carried out and it was OK, no oil leakage/shaft play, there doesn't seem to be anything untoward with it.

I scanned the vehicle with VCDS and there are no fault codes. It feels like there is a hell of a LOT more power to give but its just not happening. Also the clutch no longer slips leading me to believe it's definitely not as powerful as before.

  • Off the top of my head I'm thinking boost/vacuum hoses
  • Possibly the fuel filter
  • MAF sensor
  • Could it be possible clutch is completely knackered and engine is limiting torque as a result?

I have VCDS/VAG-COM if anyone could let me know which blocks I should be measuring I can post a log.

Appreciate any guidance as the lack of power is really doing my nut in.
 

fouryoghurts

Registered User
Look at boost pressure sensor in measuring blocks and make sure your hitting ~3bar.
If boost looks low, then you're correct, possible induction issue. You'd want to leak check the intake tract first in this case.
Air mass on is mainly for closed loop feedback on how/when EGR kicks in - but seeing as your is looped out, disconnect MAF and see how she runs on average parameters.

If boost is to spec, then fuel filter is the first easy swap out if you don't know when it was last done.
 
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freezebox

Registered User
Look at boost pressure sensor in measuring blocks and make sure your hitting ~3bar.
If boost looks low, then you're correct, possible induction issue. You'd want to leak check the intake tract first in this case.
Air mass on is mainly for closed loop feedback on how/when EGR kicks in - but seeing as your is looped out, disconnect MAF and see how she runs on average parameters.

If boost is to spec, then fuel filter is the first easy swap out if you don't know when it was last done.

Very helpful thanks. Will get on that tomorrow and report back.
 

freezebox

Registered User
Look at boost pressure sensor in measuring blocks and make sure your hitting ~3bar.
If boost looks low, then you're correct, possible induction issue. You'd want to leak check the intake tract first in this case.
Air mass on is mainly for closed loop feedback on how/when EGR kicks in - but seeing as your is looped out, disconnect MAF and see how she runs on average parameters.

If boost is to spec, then fuel filter is the first easy swap out if you don't know when it was last done.

Had it up on ramp and pipes disconnected from the turbo, intercooler pipes have a lot of oil in them and there seems to be play in the shaft, looks like a new turbo is required.
 

fouryoghurts

Registered User
What pipes were off exactly? A pipe blowing off could be due to, to state the obvious, insecure clips or a downstream issue (blocked exhaust). Oil in pipes is no big deal unless excessive. How much play wee talking about in turbo shaft?
 

freezebox

Registered User
What pipes were off exactly? A pipe blowing off could be due to, to state the obvious, insecure clips or a downstream issue (blocked exhaust). Oil in pipes is no big deal unless excessive. How much play wee talking about in turbo shaft?

Hi mate,

Big black pipe going into the turbo at the top (sorry i cant be more technical lol) and also took off the intercooler pipes and checked all other pipework around turbo. It was a well known family mechanic who did it for me (wouldn't scam me). He said in his opinion there was too much play but I didn't get the chance to actually feel it myself, the vanes of the turbo appeared to be solid though, they didn't look malformed in any way.

How could I check for a blocked exhaust? Was going to use this as an opportunity to buy a hybrid turbo but don't want to spend money unless its necessary as its ****** expensive!
 

fouryoghurts

Registered User
Does the pipe just blast off after re-securing? I'm sure your man is correct on the turbo report...I'd just proceed with caution as I've seen many a turbo "out of spec" but still boosting fine...you can get away with some play, so long as not excessive. Confirming oil feed to turbo probably a good idea too.
Re potential blocked exhaust: need to check the back pressure in the pipe (gauge screws into lambda port).

PS - if you PM me your VIN I can check some system specifics for you.
 

freezebox

Registered User
Does the pipe just blast off after re-securing? I'm sure your man is correct on the turbo report...I'd just proceed with caution as I've seen many a turbo "out of spec" but still boosting fine...you can get away with some play, so long as not excessive. Confirming oil feed to turbo probably a good idea too.
Re potential blocked exhaust: need to check the back pressure in the pipe (gauge screws into lambda port).

PS - if you PM me your VIN I can check some system specifics for you.

Turbo is definitely getting oil to it, pipe doesn't blast off it stays put.

PM'd you the VIN.
 

freezebox

Registered User
Does the pipe just blast off after re-securing? I'm sure your man is correct on the turbo report...I'd just proceed with caution as I've seen many a turbo "out of spec" but still boosting fine...you can get away with some play, so long as not excessive. Confirming oil feed to turbo probably a good idea too.
Re potential blocked exhaust: need to check the back pressure in the pipe (gauge screws into lambda port).

PS - if you PM me your VIN I can check some system specifics for you.

Hi Mate,

Took the car out just now connected to vag com - gave the laptop to my dad and we got a log of the boost pressure. Under full boost/acceleration the car is showing 2601mbar with an idle boost pressure of 989. In 2nd gear car seems to run out of steam at around 2.5k RPM but then shifting into 3rd seems to pick up again through the whole rev range?

Appreciate all the help.
 

fouryoghurts

Registered User
How goes!
Okay, so idle boost figue (i.e. no boost) at ~ 1bar atmospheric makes sense and under load ~2.6 bar is reasonable. So I'd say your turbo isn't behaving too badly and you boost pressure sensor is plausible. Out of interest, having had a DPF delete, have your checked DPF data (soot quantity, time since last regen, differential pressure, etc) with VCDS? This A3 8P had a CAT with integrated DPF can I assume this has been physically removed as well as mapped out?
Also, lets not forget the fuel filter...never underestimate the trouble these can cause. To properly test requires decent kit, but seeing as they are cheap as chips, if you don't know its history bang a new OE one on.
 

freezebox

Registered User
How goes!
Okay, so idle boost figue (i.e. no boost) at ~ 1bar atmospheric makes sense and under load ~2.6 bar is reasonable. So I'd say your turbo isn't behaving too badly and you boost pressure sensor is plausible. Out of interest, having had a DPF delete, have your checked DPF data (soot quantity, time since last regen, differential pressure, etc) with VCDS? This A3 8P had a CAT with integrated DPF can I assume this has been physically removed as well as mapped out?
Also, lets not forget the fuel filter...never underestimate the trouble these can cause. To properly test requires decent kit, but seeing as they are cheap as chips, if you don't know its history bang a new OE one on.

Yes mate DPF was gutted then rewelded up. Time since last regen was the same time I had the work done so its been mapped out correctly. Getting a full service done in a few days will report back.

You dont think the problems could be down to the clutch do you?
 

fouryoghurts

Registered User
Ideal.
So if fuel filter from service doesn't sort things, I'd still want to check low pressure supply into tandem pump before looking at high pressure and other components....the 3rd gear surging you report makes me think low pressure supply not keeping up...
For your clutch: stick the car in 4th gear (~1:1 straight through ratio) on a hill and see if it rolls - if it holds clutch is prob good. Also if engine isn't flaring up in lower gears I'd be surprised if there was an issue there....dont ignore burning smells tho :p
Hopefully all's well post service :D
 

freezebox

Registered User
Ideal.
So if fuel filter from service doesn't sort things, I'd still want to check low pressure supply into tandem pump before looking at high pressure and other components....the 3rd gear surging you report makes me think low pressure supply not keeping up...
For your clutch: stick the car in 4th gear (~1:1 straight through ratio) on a hill and see if it rolls - if it holds clutch is prob good. Also if engine isn't flaring up in lower gears I'd be surprised if there was an issue there....dont ignore burning smells tho :p
Hopefully all's well post service :D

So car is finally in the garage, getting cambelt, full service and a few other bits and bobs done, when they removed the old fuel filter they said it was black and disgustingly filthy. I get the car back tomorrow so should hopefully be sorted.
 

fouryoghurts

Registered User
Good stuff. A fuel injector cleaner (treatment) be a good addition when getting fuel filter done if your garage offers this. Let me know how it goes.
 

fouryoghurts

Registered User
We supply this and have positive results. Doesn't need to be this one...they all do the same thing really, just make sure you get the diesel one :p
The only time we don't recommend/install is for vehicles under warranty...coz it's an easy-out for the manufacturers not to pay warranty claims.
 

freezebox

Registered User
We supply this and have positive results. Doesn't need to be this one...they all do the same thing really, just make sure you get the diesel one :p
The only time we don't recommend/install is for vehicles under warranty...coz it's an easy-out for the manufacturers not to pay warranty claims.

Got the car back today and wow, feels like a brand new car, no hesitation under acceleration now and pulls like an absolute train, its brutal, turbo does however seem a bit noisy/whistly so going to have to keep a close eye on that as its probably not got much life left in it or it might be normal not sure, especially with the play that it had, but should be alright for 6 months or so until I can afford a newer bigger one lol. Going to chuck in some diesel treatment aswell as I've read nothing but good reviews for the Forte stuff so just waiting for that to arrive.

One thing I've noticed is that the new oil already seems pretty dirty, not filthy black like it was before but more a light brown, I assume this is normal in a diesel engine?
 

fouryoghurts

Registered User
Got the car back today and wow, feels like a brand new car, no hesitation under acceleration now and pulls like an absolute train...

One thing I've noticed is that the new oil already seems pretty dirty, not filthy black like it was before but more a light brown, I assume this is normal in a diesel engine?

Good news :D Re your dirty-looking oil, yes, unfortunately this is par for the course.
 
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