Had something strange happen today

[PaddyVRS]

So I went for a little blast in the VRS today as it hadn't had a good hard run in a while. All was well until nearly at the end of my drive, was sat in Manual in 3rd gear ready to overtake a truck, planted it and then changed to 4th just before redline and it just seemed to stop pulling. It actually felt like it wouldn't reach the redline in 4th gear which I have never had before. No lights on the dashboard at all, so I just continued to drive it back home although more gently. Supercharger seems to give all the boost required, but I'm not sure if it was getting full boost from the Turbo. 

 

Also, not sure if it's me but I am noticing the turbo whoosh more on boost which I thought could possibly be a leak somewhere, but again there are no lights ever appearing on the dash. 

Possibly diverter valve getting stuck/confused? Or boost leak around intercooler? 

[Ally_bassman]

Where in the rev range?

CAVE engine or CTHE?

[PaddyVRS]

Ally it was above 3.5k rpm so should be all turbo. Interestingly I went for another driver and the same thing, but after being stopped for just over an hour it was fine...

It's a cave by the way

[MattGreen]

What fuel do you use? Was the engine nice and hot at this point?

[VRSMick]

I had something similar happen on mine when there was a lack of pulling at around 80 when giving it some, as if it was noticably backing off. It went in for a dsg update, that had no effect. Then the car decided to melt a piston and there was also a clutch error which i believe was th pulling issue all along. But it ended up having a new engine and new clutch pack and pulls like a train now.

[PaddyVRS]

Have been using 95 as that's all that's available here, or e5 which is what the latest tank is. All warmed up oil at around 90 etc.

The second instance was going up a fairly steep hill, usually pulls strongly in 3rd and 4th. Today it pulled poorly in third and then wouldn't hold the revs in 4th (approx 4k)

After blasting round on my mountain bike for an hour I drove back to the motorway and booted it and voila... It was back to normal. Again have had no lights at all, and no misfires. Or at least no new ones (I get an occasional cold start rough run)

It can't be boost leak as it's not consistent, so I guess something that controls boost on the turbo as it still pulls well in supercharger range. Also when I was going up the hill there was a loud intake noise of some sort, like air being forced past or through a tight space but not a leak. This to me says the diverted valve pre-turbo

[Ally_bassman]

Could be something Turbo related? Some people might suggest the use of 95 fuel fouling the plugs. Might be worth finding someone who is able to take some logs of the car. Boost level etc to see if that shows some iffy figures.

[devonutopia]

Might have sensed some overboost or similar and put it in to limp mode?  Might not mean the CEL comes on though, but there could be a fault code logged still.  Worth checking.

[MattGreen]

My initial thought was detonation detection if on 95 fuel, but I'm not so sure. Hard one to diagnose on a forum. Really it needs diagnostics as suggested above.

[PaddyVRS]

Thanks for the help guys, appreciate it. I doubt it's detonation Matt as I have never had any problems before. Been looking through the VW TSI Engine description manual to get an idea of all the sensors so at least I have a short list of what I think could be causing problems. Already down one car in the household though so  can't really afford for mine to be off the road too, its due a service so as soon as I can it will be booked in. If I get any further problems though it will be going straight to a garage to be looked at. 

[Jabozuma]

Fuel starvation could be a problem. Causes differ, fuel pump, injectors clogged up (unlikely), fuel filter (unlikely). First one is the most likely as it can be intermittent.

When you go up that hill is the car very hot after a period of spirited driving or at normal cruising temps?

It could be a small split in a hose or I which gets pronounced with higher temps. Loose sensor wire, malfunctioning boost sensor or boost pressure sensor (wine thinks it has too much boost and bypasses).

You need diagnostics run.

[Ootohere]

A possibility is the failure of the Inlet Manifold as 'Newbie69' had, if that was what his car did have.

 

Maybe he can say what happened.

 

george

 

EDIT.  PS

http://briskoda.net/forums/topic/314698-inlet-manifold-leak-a-new-one

Edited 19 August, 2014 by goneoffSKi

[PaddyVRS]

Jabo, thanks for the insights. Hopefully it is something simple. On the whole the car is perfectly driveable and in most cases performs as far as I can tell as normal (unless ive been losing performance over time) The car had been driven on a motorway so was warm, but then was driven on residential roads for a few minutes before the "hill". Oil wouldn't have been above 95 I guess. 

 

George I don't think its inlet manifold as I would have thought it would be happening all the time (dropped a civic type R today so I think it was working ok  ) but I guess its always possible!

 

Guess its diagnostic time for me either way. 

[Furbytom]

All was well until nearly at the end of my drive, was sat in Manual in 3rd gear ready to overtake a truck, planted it and then changed to 4th

Blinkin heck you must have a long driveway if you can pull third gear overtakes on it..... Lol ;-)

[PaddyVRS]

So finally got on OBD2 reader from flea-bay to check the fault codes using the Torque app on my phone. And it came up with... Nothing. Not a single fault code stored apparently. Now I'm assuming I would get full access to any faults, but maybe there are some that only vagcom can see?

Anyway, I went for a drive to keep an eye on boost pressure while driving. I hadn't changed the units so it was in In/Mercury and not bar or psi. I found I had the peak boost of 20ish (shown as max in photo) up to about 2.5k rpm and when turbo started kicking in it dropped to around 15-16. Not sure of this is normal but I thought it would be going up rather than down.

Any thoughts?

[Jabozuma]

That is perfectly normal. Peak boost is when both supercharger and turbo are spinning. When supercharger disengages boost drops but with more revs it is still flowing enough air. In my under certain circumstances I can very clearly feel substantial boost kick at 5krpm where the turbo hits its sweet spot.

You mention photo, cannot see any photo?

[PaddyVRS]

That is perfectly normal. Peak boost is when both supercharger and turbo are spinning. When supercharger disengages boost drops but with more revs it is still flowing enough air. In my under certain circumstances I can very clearly feel substantial boost kick at 5krpm where the turbo hits its sweet spot.

You mention photo, cannot see any photo?

Hopefully the pics upload this time. I don't get any peak at around 5k. The peak is when you put your foot down till about 2.5-3k rpm and then drops off to a steady value

[Ootohere]

? You are not running 98 or 99 ron petrol are you?,  It does make a difference.

 

This is for the 125 kW engine which had maximum power given as at 6,000 rpm.   The CAVE after this is given as at 6,200 rpm

 

You will see here where they show Torque in the rev range of the 125 kW Engine,  the CAVE is much the same, the CTHE mapped a bit different.

I can link the Volkspage diagram if you want.

 

Edited 8 September, 2014 by goneoffSKi

[PaddyVRS]

Thanks for the reply George. No I'm not using super unleaded as I can't get it. The point is I haven't changed fuels, always been using e5 or standard 95, but I still think it's not as good as it was before.

It's not so much the torque values I'm worried about, but that in turbo only mode the boost isn't as high as it should be. I need to do a bit more testing to see if I'm getting a drop after s/c cutout or if it's just wastegate preventing over boost.

[fabiamk2SE]

? You are not running 98 or 99 ron petrol are you?,  It does make a difference.

 

This is for the 125 kW engine which had maximum power given as at 6,000 rpm.   The CAVE after this is given as at 6,200 rpm

 

You will see here where they show Torque in the rev range of the 125 kW Engine,  the CAVE is much the same, the CTHE mapped a bit different.

I can link the Volkspage diagram if you want.

 

I wont ask how you took those photos! Haha.

[Jabozuma]

Hopefully the pics upload this time. I don't get any peak at around 5k. The peak is when you put your foot down till about 2.5-3k rpm and then drops off to a steady value

 

It is not increasing boost pressure at 5k rpm, just the compressor wheel hits it's sweet spot for efficiency.