S4 Boosting problems even with new Turbos?!?

[killerabbit]

Hello there,

First post and its a real doozy.

I have a 1999 Audi S4 biturbo, about a 2 month ago id noticed that the S4 was starting to loose boost at the higher revs and that the power was just dropping off at about 4000rpm, this has never been a problem before but i took it to the garage anyway where i was shown that the Dumps were not holding a vaccuum and letting off and that this was most likely the cause. I was told to come back in a week when the parts arrived.

On the way to the garage to have them fitted i hear a very sudden blow out of air rapidly leaving a pipe(sort of like a ballon being let down very fast) and since i have had practically no boost. When taken to the garage she was boosting at 0.2bar, unusualy low. We proceeded to inspect and found the CV boot was torn and was quickly replaced. this however did not solve the problem and in fact i started having very low whinning noises coming out of her, these low whinning was put down to the tubro bearing gone and was in the early stages of failure which we thought would explain the complete lack of boost.

So finally the turbo bit the dust and went about a week later, smoke and all. and have since been replaced with stock OEM K03s as well as the associated pipes and gasgets costing around £900 and all been put back together. But the problem is still there. The whine has gone but the car still only boosts at 0.2bar.

No this we are stumpt on, we have found no splits/tears in any of the pipes. intercoolers are all ok, and no faults being shown onthe diagnostics. The only recomendations so far are that a sensor has gone down and not shown up (take your pick what that could be) or the ECU is faulty.

I am really getting desperate now as this is costing a fortune to keep trying things that dont work, has anyone experienced anything similar or knows of any possibilities it may be?

Thanks in advance

Billy

[baltiboys2]

Can be a number of problems faulty Maf knackered N75 valve there must be a fault code of some description need to get it on Vag-com or go to audi

cheers Raj

[killerabbit]

It is with an Audi garage at the minute and the VAG comes up clean as a whistle. My orignal thought would have been the MAF as it just seems that it is either having a restricted air flow or the new turbos are faulty. Considering the pipes were all out and inspected i guess the prior is rulled out. just not sure where else there could be a problem apart from a failed sensor that hasnt realised that its failed.

Billy

[HomerSimpson]

I think you may be correct in ruling out the MAF as being faulty, usual symptoms of that are a loss of power, going into limp mode when pushed hard and black smoke from the exhaust. All it does is sense the airflow and sends a signal to the ECU, which the ECU uses to work out how much fuel to supply. If it is not working then it goes to a default setting. I also belive that a faulty MAF doesn`t always show up on a VAG-COM. Sorry I can`t be any more help than this, but at least you can probably rule out one problem.

[killerabbit]

No thats alot of help. That being said I think I will try a different MAF all the same, just to make sure, especially if it does not show up on VAGCOM. Were having another look at her tonight (as my friend is an audi mechanic) so will get back in the morning and see how it goes.

Bill

[HomerSimpson]

Hi again Bill,
Forgot to mention that if you want to check the MAF, simply unplug it and then try it. If it runs OK then you have found your problem, also I have just been looking through some old posts and found the following, albeit for the A3, but might be what you are looking for.

"The only accurate way to test the boost is with a diagnostic tester reading the MVB (mesaured value blocks) its checked in 3rd gear full throttle at 2000rpm untill 3000rpm. Air mass meter and charge pressure control solenoid valve can cause lack of power somtimes even without a fault code stored."

[killerabbit]

Brilliant, thank you. I will try this later also. Fingers crossed.

Bill