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Right, recently I pulled the engine and box to replace belts, waterpump, clutch, turbo's etc.
Since putting everthing back together the car has been overboosting. This weekend I thought I found the problem in the guise of a torn throttle body boot.
Replaced this and things were a little better but still overboosting.
Next I replaced the MAF and then the N75 valve but still the problem persists.
On the way home yesterday I thought I would run a few tests on VAG-COM.
The car is boosting to 2540 mbar! and then the ecu shuts the boost down.
Ok so next test, I unplugged the N75 and carried on the journey home, the car was running a lot flatter as expected but then after clearing the maximum boost limit exceeded code down ...... WOW
The car is now boosting to and holding 2500 mbar (1.5bar boost) and is going like a rocket.
As good as this is I cant help feeling that something is going to break.
My conclusions at the moment is that there is a leak somewhere between the N75 and actuators which is acting like one of those boost bleed valves or a problem with the actuators themselves.

Anyone got any other suggestions ideas that could be causing this?

In the meantime im awfully tempted to chuck it on the rollers to see what it is pulling at 1.5 bar

Right, recently I pulled the engine and box to replace belts, waterpump, clutch, turbo's etc.

Well done mate!

Regarding problem you have don't have an answer for you however you could try a pressure test(?) to nail your thoughts about a leak.

Also remember reading that it may be possible to get some of the loom connectore the wrong way round?

The actuators are known to jam (I can't remember which side it is that's the problem) but I have personally seen this on 2 S4's and heard of quite a few more in the UK.

what turbos do you have? I think K04s are about at their limit with 1.5bar above atmosphere, but K03s would most likely be rather unhappy! with that much boost I hope your fuelling system can cope or you might start killing lambda sensors or worse still melting pistons

The turbo's are K03's so yes I am a little concerned.
At present the fueling seems to be coping ok (verified on vag-com), the map I have is setup to run upto 1.3bar so not far off.
Im glad you said about the sticky actuator as this was another thought.
Up on the ramps again this weekend me thinks!

As others have said, your K03's will not last long at 1.5 bar. 1.3 is too much for them also I think most map have 10psi at the redline from memory, so .6 bar.

What about an MRC healthcheck ?

Well the map I have peaks at just under 2300 mbar which seemed to work fine for me although your not the first to say its high. Infact I have only just changed the turbo's which were the original ones at 140K the remap being done at 60K so not bad going IMHO

My K03s have been peaking at a tad over 1.3 bar for the last 50,000 miles (about 5 years). Although I'd rather like them to start dying as an excuse to get K04s, they seem and sound as healthy as they were when the remap was done!

There is a BIG difference between peaking at 1.3bar and holding 1.5bar to the redline!

When loggin my car it showed that the Amd remap was peaking at 2200mbar so I don't think it is that uncommon.

John

Nige_RS4 wrote:There is a BIG difference between peaking at 1.3bar and holding 1.5bar to the redline!

I think he meant by holding as the ECU didn't chop it back. He didn't say to red line

I think he meant by holding as the ECU didn't chop it back. He didn't say to red line[/quote]

Sorry, yes this is what I meant, it peaks at 2500 - 2540 at the moment but does not hold it to red line.

Thinking about it Nige's comment about the sticking actuator may be the case. Mihnea posted a comment about the drivers side actuator getting caught on the heat shield a while back and that it is not un-common. And during the lowering of the engine back into the bay, I managed to catch the drivers heatshield and bend it a little. I did try to straighten it back up but maybe I did a little too much
Good place to start though cheers guys.

1.3 peak at 4k rpm is OK. The stress on the turbos increases with rpms, so anything above 10psi (or .7 bar) at the redline is bad. If you reduce 1.3 bar down to .7 bar in a straight line from 4-7k rpm you have a sensible boost level for a K03'd car IMO.

I have experience of a map that was above this, I know of a few but they kill K03's. Obviously a lot depends on how a car with one of these has been driven, 2 full on ring laps = dead turbos.

OK, so you've proved that I drive like a granny. Not fair!