3.0tdi boost hesitation

Gmac

Gmac

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Morning folks… I’m looking for any insight in to this issue i have with the car… I’ll try and best describe it…. But boost hesitation would be the best description for it. So when im cruising about 1800rpm, and say in forth or fifth (doesn’t actually matter what gear I’m in, but definitely the rev range around the 1800 mark) and i press the accelerator theres a definite delay whilst it feels like boost pressure is building and then sort of goes ‘there you go, there’s your boost’ and off the car goes and accelerates on boost as normal. It almost feels as if the car decelerates initially, like theres no power at all. I often box down in to a lower gear (in to higher rpm band) to drive round the problem. The car wasn’t like this when i first got it about a year ago now And I’d say the problem is getting slowly worse. I cleaned out the egr and intake about 5 months ago as they were pretty coked up.

What do we think the issue it here? I’ll scan it for codes this morning using vcds see if that throws any light.
 
Could be a boost pressure loss , a scan may show more, maybe worth checking for loose or damaged hoses too.
 
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Dirty vnt mechanism on the turbo and if that is the case you might want to clean the complete intake too.
 
Gmac said:
What does vnt stand for?
Click to expand...
Ask Google... basically you got a turbo that is variable because of the VNT... that mechanism gets stuck when it's dirty... clean it and power delivery will be smooth again.


Variable Nozzle Turbine aka VNT.... look it up you'll need to understand what to clean and how to do it.
 
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Scanned the car, no fault codes relating to this issue. Watched a couple of YouTube videos on how to remove the turbo, quite an involved job. It’ll need to be done when i can get it off the road for a few days without needing it. I had a basic look over some hoses, but still working out what’s what under the engine cover! A lot of stuff packed in to the engine bay with these v6’s!
 
Not that hard find the vacuumlines... and follow those 9 out of 10 times they have cracked if oem or if they have been replaced with silicone ones they've touched a heat source and melted. But if that was the case it wouldn't go hesitate... it would simply not give you that boost at all and go into limp mode.

This is why I pointed to the vnt mechanism as this is how it shows there is a problem with it's mechanism. To go worse overtime and go into limp mode.

Speaking from 15 years of experience driving vnt turbocharged diesel engines (not all from the VAG concern by the way) this problem is basically part of having the pcv gasses with their oil mist return into the intake + having an EGR system returning exhaust gasses with soot particles into the intake too. This turns into some tar like sticky goo that coats the complete intake and the VNT mechanism too.

Either delete the egr or plumb in an oil catch can and this will never happen again. (That is if you keep emptying the oil catch can )
 
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So just to keep this theres up to date…

Removed the turbo… BorgWagner KKK BV-50… took it apart, cleaned up the internals with Mr Muscle oven cleaner, replaced an o-ring on cold side, and put it all back together. Still got the same problem of a boost hesitation, like a slow boost build from around 1800-2000rpm. I checked the values of the output test (VCDS engine module) of the actuator arm to make sure that i had reinstalled this at the correct point. These were going from 20.9%-80.9%. I’ve read they should be 20-80%. So pretty darn close. Maybe these can be tweaked, but not sure how much movement relates to what % change. Leaving it as it is for the moment.

So i think i need to look at cleaning the boost sensor, which on my 3.0tdi is a combined IAT sensor (seems to get called a thrust sensor) and is located under the nearside headlight, so that’ll be a bumper off/headlight off job.. argh.

The car is still totally drivable but just has this slight lag. No codes and no limp mode.
 
@Gmac I replied with a link to something that is accessible, a direct link to an exploed view of how the turbo is assembled etc in your other topic... hope it'll help.
 
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Still got this, and I’m wondering if the exhaust back box delete has had anything to do with it? The timings of when i did the exhaust and the problem starting could be around the same time. Differing back pressure perhaps, i get that diesel whistle now on overrun… so may be its a pressure thing from exhaust side..if the revs are built slowly from low revs, 1300rpm, and it builds slowly then by 18-2000rpm, when the problem is most obvious, the problem doesn’t happen.
Thoughts?
 
Nah it is too far down the line to have an impact... unless you went big bore straight pipe from the turbo, in that case you'll need a remap.

The vnt mechanism.might have ware or still has some dirt in it... you can always load it up with some penetrating oil and see if that solves it.. but if that doesn't last you might have to replace the vnt mechanism.. and instead of doing that I'd go for a rebuild turbo or a hybrid (and have it remapped to suit that hybrid turbo)
 
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I was thinking it might be along the lines of wear in the vnt mechanism. As i would say the problem has been getting very slowly worse. Wonder how much a replacement turbo would be. Plus I’d need to be certain that that is what the problem actually is.
 
If you really want to test it I would buy a scrappy turbo but chances are that it could have the same problem... alternatively if you happen to have someone with the same engine and turbo (that works fine) swap 9ver to test and see if it's gone...

But if I was in your shoes: Hybrid turbo and a remap... I mean if you have to replace it you might as well gain some extra torque and bhp for your hard earned money ;) and for remapping audi's the only person I would trust in the UK with a 3.0 tdi = Bobby Singh = BS Racing. And I would let him tell me what to get and do the remap.
 
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northpole said:
If you really want to test it I would buy a scrappy turbo but chances are that it could have the same problem... alternatively if you happen to have someone with the same engine and turbo (that works fine) swap 9ver to test and see if it's gone...

But if I was in your shoes: Hybrid turbo and a remap... I mean if you have to replace it you might as well gain some extra torque and bhp for your hard earned money ;) and for remapping audi's the only person I would trust in the UK with a 3.0 tdi = Bobby Singh = BS Racing. And I would let him tell me what to get and do the remap.
Click to expand...
Thanks mate :)
 
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bobby singh said:
Thanks mate :)
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No thanks, you've done stuff others still don't seem to get anywhere near when using the same hardware, let alone making it reliable at those figures. And the fact that every time I've contacted you the information I got was always spot on.
 
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Gmac said:
If i was closer Bobby, I’d have the car in to you to get it sorted! Any chance you can have a read through this thread and share your thoughts? TIA
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Without logs its impossible to guess whats going.
Maybe disconnect the MAF and go for a quick drive - if it feels better then you know the MAF is faulty.
MAF is used by the smoke limiter in the ECU - if low air flow is seen then you get low levels of fuel.
 
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Hello mate, did you ever get this solved? I got same issue on my 3.0 bitdi. Boost hesitation up to 1800rpm then the car flies. Did a egr dpf off because I had issues along the way. Ive changed turbo to a refurbished one from germany. The problem remains, cant find anything other than im getting an exhaust smell at cold starts and the hesitation.

I have defently hit a wall here. Audi couldnt find it as they would need to take down alot of stuff which would cost alot
 
A7313 said:
Hello mate, did you ever get this solved? I got same issue on my 3.0 bitdi. Boost hesitation up to 1800rpm then the car flies. Did a egr dpf off because I had issues along the way. Ive changed turbo to a refurbished one from germany. The problem remains, cant find anything other than im getting an exhaust smell at cold starts and the hesitation.

I have defently hit a wall here. Audi couldnt find it as they would need to take down alot of stuff which would cost alot
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Issue like hesitation (or most issues) are hard to determine without logs - but if I had to guess I would look at injectors as a starting point
 
Hello Bobby, ive read about you in some posts. Glad you commented. Ive had logging done by my tuner. He said my small turbo is building pressure but its somewhat choked.

Ive also thought about injectors, since one of the 6 is totally wet. I did change an o ring without any success. Should I chance and have it cleaned by professionals or what do you reckon?
 
A7313 said:
Hello Bobby, ive read about you in some posts. Glad you commented. Ive had logging done by my tuner. He said my small turbo is building pressure but its somewhat choked.

Ive also thought about injectors, since one of the 6 is totally wet. I did change an o ring without any success. Should I chance and have it cleaned by professionals or what do you reckon?
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either have it cleaned and refurbished or buy a new one... the injector when pulled should be dry, regardless if the engine just ran or has been sitting for months on end. fyi it's a leaking injector... no good at all
 
Do you think my boost hesitation could be cause by this injector? Im going crazy about this. Every mechanic sais no about boost and injector issues i will try and refurb this one injector but would like some confirmation
 
The answers is no... a leaking injector will cause misfires if left long enough, since there is fuel dripping out of it when it should be closed.

Boost issue might be a worn turbo core, to much play on the shaft, a sticking vmt mechanism or a vacuum problem (read perished vacuumpipes especially if you still have the original cloth covered vacuum pipes , you can't see if they have splits etc)

So I would address the leaking injector, and start with replacing all the vacuum pipes with silicone versions. That way you can rule them out. Plus it's the cheapest thing to start with.

If that doesn't solve it the next stop is to check the turbo vnt mechanism etc etc etc... trouble shoot 1 thing at a time. You'll get to the bottom of it.
 
But I have a refurbished turbo inside. And I read about similar problems on forum where they also have checked turbo and nothing wrong.

I did change O ring for the injector.

Regarding vaccum. I did have vaccum loss from the egr cooler. The sealing had worn out. Now I changed it and im not having limp because of that. But still the bad boost under 1800rpm. Thanks for all the answers much appreciated
 
Bad boost under 1800 rpm? so you just replaced the turbo yourself and didn't adjust vnt lever rod? well that might be the reason why it acts like that... FYI reconditioned turbo's do get calibrated but not on your engine so will always be ever so slightly off... solution is the distance of the actuator rod on yours needs shortening. it's not hard to do, if you look it up you'll find out how to do it ( look on youtube)
 
I replaced it by a mechanic. And I also heard it needed adjusting. Its the small turbo, you think just adjusting it alittle by hand can solve the issue? I think I might try to do it but im scared to do something wrong
 
Quarter turns of the nut, but first mark where it sits right now so you can always put it back. In the location it sits right now.

As I said it's not hard just need to mark where it sits now and you can adjust it. If I'm correct the boost should start to be noticeable at 1500 rpm. So it's just a few turns off the mark.
 
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If this is a BV50 turbo you can not just adjust the stop screw, the actuator needs to be programmed for the the open / closed positions based on the flow via the stop screw.
Best to do this on a flow bench.
If you get stuck drop me a email
BobbySinghRacing@outlook.com
 
completely forgot about the BV50 turbo being fully electronic operated, still needs calibraion though as his boost starts to late.
 
northpole said:
completely forgot about the BV50 turbo being fully electronic operated, still needs calibraion though as his boost starts to late.
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They have a stop screw but it needs adjusting according to flow and then the actuator needs programming (not something that Vcds can do )
Cheers
 
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805713-5009S Garrett GT3067S+GTB1749VK

This is the turbo unit on my car. Its A7 2013 3.0 BiTdi so 313hp original. Its the small turbo, my tuner logged it he said its buldiung pressure but not until 1800.

Here is also a video of the small unit on a car.
View: https://youtu.be/L2MIbudFFyk?si=ZqjDW8rfx2PcS-cY

Really thankful guys since ive really run out of help to get. And it seems you guys know whay your talking about for sure.

Also im getting a smell of exhaust in the cabin, maybe its related.
 
A7313 said:
805713-5009S Garrett GT3067S+GTB1749VK

This is the turbo unit on my car. Its A7 2013 3.0 BiTdi so 313hp original. Its the small turbo, my tuner logged it he said its buldiung pressure but not until 1800.

Here is also a video of the small unit on a car.
View: https://youtu.be/L2MIbudFFyk?si=ZqjDW8rfx2PcS-cY

Really thankful guys since ive really run out of help to get. And it seems you guys know whay your talking about for sure.

Also im getting a smell of exhaust in the cabin, maybe its related.
Click to expand...

Plastic gears inside the actuator have a habit of rounding off etc but this normally a indication the VNT is sooted and should throw MIL.
But I've tuned so many of these BiTDI's now over the years only changed two.
 
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I think it's best you PM bobby as he's way more knowledgable than me, plus he tunes these engines often enough, so he'll be able to help you better.
 
Hello guys its not the bv50.
My car is Audi A7 2013 with 3.0 BiTdi engine of 313hp original.
Its a two turbo unit device.

Turbo:

805713-5009S Garrett GT3067S+GTB1749VK​


Can you please look at it? Also have a video of it.


View: https://youtu.be/L2MIbudFFyk?si=koTVORcFtORbsGVg

You guys seem to know alot. Any help is much appreciated.
 
PM Bobby he knows way more than i do and wha he doesn't know means is not worth knowing ;)
 
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Morning folks, I’ve never got to the bottom of this issue, just been running the car as it is. Car still running the same as always, no limp modes, i just have to be patient around the 1800rpm mark for the boost to build. Lol. Very used to it now, and 90% of drivers probably wouldn’t even notice the issue! Interesting to read about the flow of injectors is this something that i can use vcds to look at? So to recap.. had the BV-50 turbo off cleaned and put back on, intake and egr all cleaned fairly recently, and intake flaps checked and working as they should..
 
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