2.0tfsi quattro BUL going into limp mode when boosting.

[Bundles]

Hey folks, long time lurker first time poster.

I've had my A4 2.0tfsi quattro special edition (longest car title ever!) for a little over a year but recently, ok not recently, over 6 weeks ago but i
I'm a postie and been pretty busy, time of year and all... anyway the car started going into limp home mode whenever it boosts. If i drive it VERY carefully so as to keep it off boost she runs fine, but if i deliberately make it boost (or even accidentally) it goes into limp home mode and can't even get out of it's own way!

It's not an intermittant problem as it happens every time the car boosts other than if i have to launch it out of a roundabout in 1st, it takes off like a train, but once into 2nd and boosts it drops into limp mode. Any gear, any speed, if you give it enough theottle to boost it'll drop to limp mode.

The most annoyingthing is that it has never, ever given a fault code and i really cannot afford to replace bits and find out there was nothing wrong with the old one so i would really appreciate any and all help in arriving at a likely diagnosis.

Thanks in advance.

Bundy.

[zollaf]

no fault codes eh, what have you been diagnosing it with.

[Bundles]

I have a bluetooth adapter and have used Torque. I also have an obd cable and have tried vag-com and vcds, although ii admit i'm not overly adept at using either but neither returned any codes. Oh, and a friends cheap hand held code reader, still nothing.

[zollaf]

ok, so how i would go about diagnosing this, first you need to see what the ecu sees. i am very surprised there are no codes. a full scan would help , see whats in other systems other than the engine, then go for a drive whilst looking at live data and see whats actually happening when it drops power. if it is limp mode then there will be codes, its upto you to find them. once you can see what is happening, like boost pressure desired and actual, all the temps, air flow meter, then you can decide what is causing it. there is no other way without replacing bits as you like, but as you know, thats gonna cost.

[Bundles]

Im pretty shocked there has never been codes myself. im leaning towards n75 or diverter valve myself but thought i'd seek some 2nd opinions.

looks like i'll have to research a game plan for vag-com, ie channels to watch etc.

[zollaf]

there is avcds map of users. you could find someone local with it to help you.. look in the vcds section. if boost actual exceeds boost required by a certain amount then it drops the fuelling to save the engine. this is limp mode. so this generates a codes, boost pressure exceeded. no code means its not gone into limp. so does it gointo limp ad then its down on power until you turn the ignition off and on again, or does the power return as soon as you back off the throttle.

[Bundles]

It looses power completely to the point it wont pull up hills and lorries pull away from you. It's fine again once you turn the ignition off then on again.

[zollaf]

does sound like limp mode but might not be limp mode. you need to get those codes read and look at live data to proceed really. i presume you have checked in the engine bay for any split boost hoses or anything that doesn't look or sound right. have a good feel of the hoses to make sure one isn't split and you can't see it.

[Bundles]

Yep i've checked for split hoses and all appear sound. I haven't checked if its running the old or the new style diverter valve. it had a new turbo at 98000 miles 3000 miles before i bought it so i (maybe wrongly) assumed it would have the newer sort. The car is 108000 now.