Boost check on VAGCOM (VCDS)

[burkey1]

Folks,

It's probably half a mech topic, half a VAGCOM topic but I decided to post here..

Im looking to check the boost on my A4 1.8T.

Ive done some looking around and found that I should be comparing measuring blocks

114-4 N75
115-3 Specified Boost
115-4 Actual Boost

Can someone give me the correct procedure to complete this on VAG scope.

Do I just floor the car in 3rd while driving all the way from to 2000 to 6000 and record scope values?

Should I foot off the pedel when RPM reached...??

What should I see in all 3 measuring blocks, N75 switch point, max specific/actual boost, how close should they map each other etc.....

Would appreciate any advice here...

02 1.8T AVJ 150bhp
VAGCOM 409.1-S

[martin1810]

Try here for how to do it.
http://www.ross-tech.com/vcds/tour/logging.html

and this will give you some idea of what you should get.
http://www.audi-sport.net/...vag.../...t-vag-com.html

[burkey1]

Tks Martin,

Was unable to connect to the audi-sport.net link. Suspect it has something to do with my work PC therefore will try again later at home.

I suppose the real question I am asking is: How do I perform the test?

Below is what I intend to do. Can you tell me if this is the correct procedure or not

· I intend to map the below measuring blocks along with RPM on VAG scope.
114-4 N75
115-3 Specified Boost
115-4 Actual Boost

· Floor the car in 3rd gear from 2000rpm to 6000rpm.
· Take the foot completely off the accelerator when 6000rpm reached.
· Post graph results for analysis

Also what should be the max boost for my car and what rev band width should I see it in.

Cheers for info thus far…

[martin1810]

Yes that will work. Max boost is about 2.0 bar and comes in near 2000 rpm. Varies a bit so don't expect exact figures.
Try this link instead.
http://www.audi-sport.net/vb/vcds-fo...t-vag-com.html

[burkey1]

Tks again,

I think those figures sound a bit like diesel figures as would have expected a little lower boost and abt 3000rpm for petrol engine boost.

Will try later on and post results.

cheers mate.

[martin1810]

Don't forget it is a VNT turbo so you get a much more even spread of boost and no dump valve at the end. Generally the most important infor is that the two traces match reasonably well. (Requested boost and Actual boost). The boost request is part of the ecu map so if the actual is "way out" you know something is odd. If the Actual boost is well out, the engine usually throws a fault code. Have fun. Don't drive and log. Get someone else to log.

[burkey1]

Cheers..

Whats a VNT turbo?

Graph attached is maxing at just under 1.6 bar and actual appears to be tracing well from what I can see.
Was hoping for a little more though!!

Is the N75 operation ok?
Am I right in saying that when at ≈90% the valve is almost closed and almost full exhaust gasses are spinning the turbine?
Is it correct to tail away like that over the rev range?

Any info appreciated..

Thanks

[martin1810]

That looks fine to me. The N75 is working ok as it is regulating actual boost closely with requested boost. In an ideal world you would want the graph to remain level longer rather than slowly falling. But as the boost is following the requested boost, you are getting what you should. VNT turbo means the vanes in the turbo move according to vacuum supplied by the N75 valve. So instead of dumping boost through a dump valve, the N75 reduces vacuum pull on the VNT mechanism by bleeding vacuum off. When it does this the turbo produces less pressure.

[burkey1]

Thanks again Martin,

Always wanted to confirm this as never really felt the car was performing to its factory capabilities.

VTN turbo works a little different to what I know a turbo to work like, but same principles..

One last one...

Is 1.6bar max peak a little low, or is this correct for my make and model??

02 1.8T AVJ 150bhp

Cheers..

[Crasher]

The 1.8T does not have a VNT turbo...