(VCDS) Difference in Boost Pressure: specified VS actual?

[AudiB720TS]

Hi guys,

I did my first data-logging last night with VCDS.

One thing that I see is that "Boost Pressure (specified) mbar" is different from "Boost Pressure (actual) mbar". For example, at 6040 RPM specified boost is 2130 mbar, but actual boost reads at 1850 mbar.

I don't have a known healthy baseline to compare with, so I wonder: is this a source of concern?

Here's a snippet from what I am seeing:

Full log (PDF) here

 

[i3oricua]

I saw your post on Audizine but didn't want to inject into what other were saying.

I only converted your screenshot. If you post the excel file it would be much easier for me to convert but you're losing boost in the upper RPM. That could just be the turbo running out of steam but logging and converting the whole RPM range would tell us more.

 

[i3oricua]

So I got bored and typed in all your data and created a graph. Make what you will of it. I'll give you my opinion.

I can't remember who you said your tune is by but they have the ECU requesting boost early and you're hitting full boost around 2300-2500 RPM and then you can see where the turbo just starts running out of steam towards the end of the rev range. I think you have a boost leak somewhere because the lines on the graph should be evenly matched most of the way through until the smaller K-03 just starts running out of steam. But it seems you spike and then run out of steam relatively early. But that shouldn't be until maybe 5500 or so that it starts losing and even still it shouldn't be dropping all the way to down to almost 10 PSI.

That is my opinion.

 

[i3oricua]

The last thing I'll say is that I feel that you should be requesting more boost than 17-18 PSI. That may just be a bad formula I used but you should be seeing 20-22 PSI requested on an aggressive tune and your actual should be matching it. I think a stock tune is around 12 PSI so it's not asking for a ton more over stock. But honestly I can't remember what the car is tuned at stock in terms of PSI.

 

[Charlie Farley]

That's lot of work you have done there Edgar, I hope the OP is greatfull for your input, nice to see such a comprehensive reply.

 

[AudiB720TS]

Yes, of course. Thank you very much for doing that! Very helpful.

On one hand the car feels really strong and it dynoed 225 hp (228.5 metric hp) too the wheels (say 270-275 crank hp) and then on the other hand the data-logging says clearly that there is an issue, and that the car is getting less boost than it should. So I want to think that I fix this and do another dyno it should be a really good number! Not that this matters at present.

Full boost at 2500 RPMs seems strange, no? I have to ask JHM why its requested that early. Because the EU standards emissions test for "fast idle" is at exactly 2500 RPMs having full boost there might not help me in passing the emissions tests, even with stock cat hahaha...

I updated my "build thread" on the US forum, but I think I have a leak in the wastegate possibly, so maybe course of action now is to get a replacement K03 turbo AND put the stock cat back for emissions tests. Assuming that clear the boost irregularities and gets me past emissions tests, I can then look at the stage 3 in the next year (will source the Airtech IC kit from the UK before "brexit" though to avoid customs fees).

Probably too late with this info, but here (link) are the full logs in original CSV format.

 

[i3oricua]

You hitting full boost at 2500 is fine as long as it’s not a K04. If it was a K04 you would snap your rods because of too much torque too quickly instead of a gradual increase. The tune is requesting full boost way earlier than that which is strange as I feel it should be a smooth curve to match your actual. Again, the graph should match each other in terms of requested and actual.

I wouldn’t just assume it’s the wastegate without ruling the other things like DV, valve cover and vacuum pump first.


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[AudiB720TS]

without ruling the other things like DV, valve cover and vacuum pump first

I have GFB DV+ diverter valve. I inspected it best I could yesterday. It seems fine. I have ordered the latest revision (G) stock diverter vavle this morning so I will switch to that and see how it runs. I did break the electrical connector (the "lock", not the connector per se) on the wiring to the diverter valve but it is installed tight (added some PL300 on the outside) with no play. Ordered a new connector as well, just in case.

Vacuum pump? This guy(?):




If I had a vacuum pump issue wouldn't I have other symptoms on pretty much anything requiring vac?

 

[i3oricua]

The video link doesn’t work.

Not necessarily. It could be leaking slightly and you not know except for it would be a little noisy and sound like you’re cam chain is rattling.

Do you get any codes? Specifically P0299?


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[AudiB720TS]

I only had a stored fuel pump related code (P3089) a few days ago, I cleared it and it has not reappeared.
Pretty sure that code was from pulling the fuse when doing a compression test on the car (I crank with the fuel pump disconnected).

 

[i3oricua]

The video worked here at home.

That is the vacuum pump. It typically leaks vacuum from the nipple. There is a small o ring inside that tends to get old and dry and start to deteriorate causing air to escape and makes a rattling noise too.

I would def try a stock DV valve to see if that helps. You should be able to feel the difference but logging is your best bet.

If you can find someone to do a boost leak test (smoke test) then I would pay to have that done before you keep throwing money at parts.

 

[AudiB720TS]

Thanks,

I'll see if I can simply listen to the vacuum pump above the engine noise. It looks like a real pita to replace (and expensive too) so hopefully my pump is fine...

 

[AudiB720TS]

And I wonder if I can pressure test myself without air compressor, maybe using a bicycle pump.... I'll go research that now

 

[i3oricua]

YouTube has some videos on how to make a smoke test device for leak testing but honestly it’s just easier to pay for the test most of the time.

There’s a kit that lets you replace the o rings on the pump. Problem is only one person sells them and he’s on eBay. I’ll dig up the link and post it. Also, I’m not saying that’s you’re problem, just giving you places to look. At the end of the day everything may be fine on the car and you have what you have.

Edgar


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[AudiB720TS]

it’s just easier to pay for the test most of the time.

Yeah, I googled it in local language. Lot's of ppl asking for it on various Swedish forums, but no place offering it.
This sort of tester might be good to have so I will probably build one as a bit of a side project and test if a new dv doesnt help.
Okay, I'm done with the coffee: going outside to listen to that pump now

 

[AudiB720TS]

OK: No suspicious sound from vacuum pump during idle at least.

I also drew a line on the coolant level in the coolant reservoir / overflow tank to monitor that going forward (the car smokes a bit more when warm than when cold and I want to rule out it burning coolant through head gasket).

 

[i3oricua]

OK: No suspicious sound from vacuum pump during idle at least.

I also drew a line on the coolant level in the coolant reservoir / overflow tank to monitor that going forward (the car smokes a bit more when warm than when cold and I want to rule out it burning coolant through head gasket).

I’m actually glad you brought that up. You’re not likely burning coolant but you are likely burning oil which is due to faulty valve cover. The only real fix for that is a new valve cover. You likely have oil in your intercooler pipes and maybe even some in your turbo too.


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[AudiB720TS]

You’re not likely burning coolant but you are likely burning oil

Yeah, I think so, but nice to rule the coolant out.

which is due to faulty valve cover. The only real fix for that is a new valve cover. You likely have oil in your intercooler pipes and maybe even some in your turbo too.

Why do you suspect the valve cover, is it because my comment on PCV on the other board? I have some doubts about the vc but I also just checked by removing the catch can dipstick and it blows air out with healthy pressure so I assume now that PCV works both on the turbo side and on the PCV side.
One thing I might do later is to lower the installation point of the catch can do get more of a gravity pull through the hoses (right now they are pretty much level with the vc, wheras the pipe from vc to turbo inlet is at a steep angle).

 

[i3oricua]

I did see your post on the other board but it was just minutes ago and after I posted here. That just added more to my suspicion that it is your valve cover. There is a test you can do to the valve cover which requires you to remove it and blow through one of the ports. I don’t know the steps but it could tell you more about the status of your valve cover.

What color is your valve cover? The gray ones are known to have problems. The black ones are less problematic but still fail.


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[AudiB720TS]

What color is your valve cover? The gray ones are known to have problems. The black ones are less problematic but still fail.

It's black. 2007 model year (2006 build). About 63.000 miles on it.

 

[AudiB720TS]

Just found this:

Kind of sounds like what I am seeing (oil in turbo inlet, none i catch can).

 

[Charlie Farley]

It's not just the valve cover that is different on the Early BUL engines , numerous parts were revised all over the engine , the early BUL engines are also known for problematic PCV 's , well all the pcv's are problematic on these engines but some more than others , very much like the cams and cam followers etc, goes with the territory really.

 

[Charlie Farley]

Just found this:

View attachment 163704

Kind of sounds like what I am seeing (oil in turbo inlet, none i catch can).

do you have a catch tank connected to the VC outlet ?

 

[Charlie Farley]

You will never stop the oil finding it way out with these engines , that is just the way there are, well almost all turbo engines suffer from the problem ,some more than others and the 2.0tfsi is most certainly "more" .
Unless you have a system in place that removes the oil and other contaminates directly from the VC outlet before returning the air to the turbo or vent to atmosphere , you will just keep getting it the turbo, IC's and beyond, you need to get it out of the system.

 

[AudiB720TS]

Sure Rob, but it does appear from researching the routing inside the vc, that it should primarily exit on the PCV side.
It's just a bit fishy that the turbo side gets so much and the PCV side virtually nothing.

 

[Charlie Farley]

What guys fail to realise is that these engines drink oil under normal tuned state from the factory , audi openly state the levels of consumption in the owners handbook, they are not trying to cover it up , owners don't realise what is normal for these engines.
If you use a lot of right foot on a regular basis oil will get used quicker.
Now add into the equation of uprating the power etc and yes the oil consumption issues are made that much worse, owners just down take that into consideration and compare the factory consumption level with an engine that may tuned to stage 2 or 3 and wonder why its drink that much more......obvious really.
My old bus still drinks oil, if I drive the car the way it should be then it will use a fair bit, If I just crawl along and just go with the flow then it is much less.

 

[Charlie Farley]

Sure Rob, but it does appear from researching the routing inside the vc, that it should primarily exit on the PCV side.
It's just a bit fishy that the turbo side gets so much and the PCV side virtually nothing.

If you look at a cross section of the VC and its internal routing of PCV venting etc you'll see the problem.

A catch tank needs to be level with the top of the engine or slightly below , not higher , and the more vacuum that can be used to draw the gases out and recirculate the better.