Where is my boost gone?

[quattrokid]

Just had my UrS4 MOT'ed... it failed its emissions at the main dealers 3 months ago.... now passed without any fettling

it was noted that the boost doesnt "feel" as urgent as it should be,its still a reasonably quick car but its not as fast as it should be..... being accustomed to the RS4's performance coming down 150 bhp or so WILL make the S4 "feel" slower now I have had a quick chat with an Audi engine specialist and it sounds like without doing log runs or a vagcom check that the N75 boost control valve could be on its way out.

is this common on these engines? dread to say that mine could be the original fit in which case 215k miles isnt bad going!!.

all hoses have been checked and are tight, no leaks, and the turbo spindal has been checked and thats fine to.just as well since its a fresh turbo in there!!!

where is the N75 on a 20v lump please and is it an easy swap?

[PeterB]

I think you'll find that I replaced the N75 valve Rich. I usually change that as a matter of course if it's elderly or even the original one, and I'm sure that I did the S4's.
And I did the 710N diverter valve too, as well as the bloodly MFTS, ecu temp sender and a nice set of Samco boost hoses. They'll all be listed in the receipts if you've kept them.

Get the timing properly checked as it may have been upset when the head was changed.
Also a pressure test will show if you have a boost leak from say the intercooler or a gasket somewhere (won't be the hoses!).

You may find that the coil packs are past they're best by now, I know that you had a couple of them changed but they usually last 100k or so. Get the POS checked too.....

[SteveT63]

Did they talk also about
Map Sensor
Throttle Switch
Throttle Boot
ISV Failure
Fuel Pressure Regulator, Very Common.
Vac/Boost Pipe to ECU
Recirc Valve... If its an old standard Bosch one, get rid....Edit...You got one!!
Diff Vac Pipes Split, will affect Recirc Valve and N75.

All stuff that was checked and repaired/replaced on my S2 which had a massive effect on its performance.

Its a long long list of stuff that if a number of things are just a little bit below par, all added up they will limit the engines performance.

[quattrokid]

thanks PeteB thats good info there as to what you did....yes of course I have all the paperwork you gave me although the replacement head I am not sure you had it, I'll have a look on Friday.
Handy for Ben to get in touch with you to see what you did as well as the car's history I have accumulated

thanks Steve, spoke to Ben tonight so he went through your list above as well.

I'll be taking the car to Ben sometime soon for a fettling and see whats going on. Judging by what Pete had done, that covers most of the list of could be's already.

[quattrokid]

it doesnt help when the re circulation valve is the wrong way round
and the throttle was only showing 74% on vag com

needs a new throttle position sensor.

2,2 bar on a test Ben did so its boosting better than it was

[john johnson]

Sorry to hear about the s4 Rich, at least you've got a slight positive out of this and found out how good ben is, been telling a few for a while! Owt with four rings new or old and he's yer man !!

[quattrokid]

Originally Posted by john johnson

Sorry to hear about the s4 Rich, at least you've got a slight positive out of this and found out how good ben is, been telling a few for a while! Owt with four rings new or old and he's yer man !!

HE COULD HAVE BROKEN ME IN LIGHTLY and say I need to replace the side light bulbs... not a GEARBOX

Ben wants me to bring the RS4 to the A.D.I..... dont think thats a good idea, lost 1 car on the first visit to him, dont want to lose another, besides the trains in this country are slow, late and shite!!!!


I'll DRIVE home this time thanks!!

now I have a spare set of UrS6 rims for sale!