RS6 Plus C5 misfiring and misbehaving

[VETRA]

Hi everybody!
I've recently bought an RS6plus with the engine misbehaving...
I knew what i was buying and being previously an owner of 80, 100, V8, S8(D2), A6(C5,2.7tt), A8(D3) I am quite familiar (at least in general terms) with how it all works.
But still - it turns out, I need your help!

So here is my story.
The engine is not stable. The idle run is floating +/- 5% - can't see it on the tachometer, but can feel it.
At the full-throttle first of all it feels like the engine is not giving it's full power.. it feels like something is holding the car's rear bumper, like she wants to ride and something is not letting her do that. the torgue, the acceleration is not smooth. From time-to-time (while holding the throttle pedal down) she suddenly shows her full power for a period and then back again (and then again - suddenly she awakens abruptly, then again half-power)...
Here is what the computer says:

Code: Select all

VIN: WUAZZZ4B95N999163 Mileage: 202080km/125566miles
-------------------------------------------------------------------------------
Address 01: Engine Labels: 077-907-558-BCY.lbl
Part No: 4D1 907 558 F
Component: 4.2l V8/5VT G 0001
Coding: 0010752
Shop #: WSC 13364 153 403078
VCID: 316F6586AB5E3096243-5072

6 Faults Found:
17985 - Right Engine Mount Solenoid Valve (N145)
P1577 - 004 - Open Circuit
18393 - Coolant Control Module 2 (J671)
P1985 - 002 - Malfunction - Intermittent
18308 - Coolant Fan Control 2
P1900 - 004 - Open or Short to Ground - Intermittent
18010 - Power Supply Terminal 30
P1602 - 002 - Voltage too Low - Intermittent
16684 - Random/Multiple Cylinder Misfire Detected
P0300 - 001 - - Intermittent
16688 - Cylinder 4
P0304 - 001 - Misfire Detected - Intermittent
Readiness: 0000 1000

What I tried already:
checked intake for leaks - didn't find any leaks;
checked turbo pressure - up to 2.2 bars (also see below);
checked air consumption - up to 300 l/s at full power (also see below);
swapped spark plugs and coils. got much better, but still no there.
swapped Mass Air Flow sensors - no significant improvement, so I put back my old ones (tests below - with the old ones)

I did a few road-tests, here is what i got:

and a couple of graphs:

Why did the Wastegate open fully at full throttle at low RPMs(<2500)??
This causes the discrepancy between Specified and Actual Boost Pressures...

I don't understand how Engine load can be 170% ??

Conclusions:
MAFs are fine.
Lambdas are fine. (Or should I take a look at some other lambdas measurements? There are many and I get lost in them)
Turbos are fine, except for strange wastegate behavior.

up next:
- Swap fuel filter, flush fuel system (probably won't cure, but still a good thing to do);
- Swap: N112 Secondary Air injection valve, N249 actuator, Diverter Valves, Fuel pressure regulator;
- I did not order N75 Wastegate actuator, looks like it works.

Am I on the right path?

[Nobby]

Seems to be running quite high boost. Thought they only ran about 0.8/1.0 bar as standard, and the turbos aren't really big enough to be pushing that much boost.

[VETRA]

Thought they only ran about 0.8/1.0 bar as standard

0.8/1.0 extra boost, isn't it? In other words 1.8/2.0 bar absolute pressure, right?

[Shoppinit]

Could just be a coil pack. Hardly a rare occurrence.

[Shoppinit]

Nice graphs, but did the problem occur when they were being logged?

/just saw that you already changed the coil packs.

[VETRA]

Yes, it misbehaves all the time.
I forgot to write also that that the car does not smoke at all. No oil traces in the antifreeze..
i haven't measured the compression though..

[Shoppinit]

Does it do it if you drive with the petrol filler cap off?

[Shoppinit]

The boost graphs look OK. If it was overboosting you'd expect a DTC, unless it was coded out. How reliable is the tuner who did the map?

[VETRA]

Does it do it if you drive with the petrol filler cap off?

Pardon?

The boost graphs look OK. If it was overboosting you'd expect a DTC, unless it was coded out. How reliable is the tuner who did the map?

This one I din't get either..
Do you think it's been tuned?
I wasn't told anything like that and I think it hasn't been tuned.
There's been 2 owners - the first one was a famous gentleman in Germany, he did servicing at officials with all the papers. So he didn't tune it.
The second was a lady and obviously she didn't look after the car very well... So I don't think she's done anything either..

And the graphs I made myself. I've got a VAG-COM---USB cable, a notebook and a VCDS software...

[Ajc]

Does it do it if you drive with the petrol filler cap off?

Pardon?

The boost graphs look OK. If it was overboosting you'd expect a DTC, unless it was coded out. How reliable is the tuner who did the map?

This one I din't get either..
Do you think it's been tuned?
I wasn't told anything like that and I think it hasn't been tuned.
There's been 2 owners - the first one was a famous gentleman in Germany, he did servicing at officials with all the papers. So he didn't tune it.
The second was a lady and obviously she didn't look after the car very well... So I don't think she's done anything either..

And the graphs I made myself. I've got a VAG-COM---USB cable, a notebook and a VCDS software...

Shopp means in its most literal sense, drive the car with the petrol cap off and see if it still does it . The tank will have a breather system and it it becomes blocked . It will create a vacuum in the tank and could starve the system of fuel . Have you changed the fuel filter and is it correct for the car ?

With the boost map, if you're sure the car isn't mapped then it could be over boosting and there isn't enough fuel . Although as said ,The car should throw up an engine management light if it sense's an over boost .

[VETRA]

Sorry.... I read "petrol filter cap" instead of "filler". My bad.. =)
Will try that!

For the overboosting - but the SPECIFIED and ACTUAL boost match almost everywhere (except low RPMs). So it will not show errors on that.
On Idle run the boost shows 1000mbar and at full load it's up to 2000mbar, so it's absolute pressure...
Is 1 (extra) atmosphere boost too much?
What is the specified boost for RS6 (googled it with no result...)

[Ajc]

Sorry.... I read "petrol filter cap" instead of "filler". My bad.. =)
Will try that!

For the overboosting - but the SPECIFIED and ACTUAL boost match almost everywhere (except low RPMs). So it will not show errors on that.
On Idle run the boost shows 1000mbar and at full load it's up to 2000mbar, so it's absolute pressure...
Is 1 (extra) atmosphere boost too much?
What is the specified boost for RS6 (googled it with no result...)

I'm not too hot on the VCDS side of things as yet . I come from an old school weber background so im still learning the modern ways . So I wouldn't want to point you in the wrong direction.

[ahoooga]

There's been 2 owners - the first one was a famous gentleman in Germany, he did servicing at officials with all the papers. So he didn't tune it.
.

You don know that he didnt have it mapped though ? , or are you assuming ?

Early revo maps where on a flash stick you put in the OBD port and could change back to stock whenever you wanted.

[VETRA]

I don't know for sure about the mapping... ( Is there a way to find out?

Tried driving with fuel filler cap off. No difference.

Noticed that the engine wakes up more often when fully warmed up. So first 5-10 minutes of driving it shows poorer performance, and then it gets a bit better...

[Shoppinit]

It must be mapped if it's asking for that much boost.