URS6 Gutless!!

[HMS-S6]

I hope someone can help me!!

I have a 1995 S6 avant (AAN) with a very long standing and very annoying running fault!

As the car reaches 2800 rmp ish the turbo starts to do its job as normal, but then as soon as full boost is reahed, roughly 100-200 rpm later the car surges horribly right through the revs, its awfull!! Although i rigged up a mechanical boost gague and the boost figures are rock steady and spot on!

However if i get to about 4000 rpm on light throttle then stamp on the throttle it pulls very well.

I have another S6 which works well and The parts i have changed car to car or for new for this fault and others are as follows: (and nothing has made even a slight difference!!)

ECU
Coil pack complete
POS units
Cam position sensor
Both crank sensors
Turbo
Cats
Valve stem seals
Check valve timing
N75 valve
Knock sensors (both)
MAF sensor
Plugs
Air Temp sensor
Checked breathers are clear
Visually checked all boost hoses
Cheked throttle sensor values
Lambda sensor

I'm at the end of my patience as i love the car but as it is, it is useless as a fast car as the turbo can barely be felt coming in dispite what the gague says!

Has anyone had/heard of this before??

[UrS4boy]

The normal suspects would be the ignition system (POSs and Coil packs, boot connectors and sparkplugs). However you say that they are all fine.

You might have a boost leak (typically the Michelin Man hose at the inlet to the OE intercooler). You need to do a boost leak test (at say 15 psi supplied by an air pump).

You didn't mention your hard starting problem (that you indicated to me in a pm). For
this, I suggest that the hard starting points at a fuel issue:

1. a leaking injector would drain the pressure down in the fuel rail (and worse, wash oil off the cylinder wall).

2. dirty injectors, not able to supply fuel as and when required by the ECU.

3. Fuel pressure regulator, not able to supply the proper 4 bar delta across the injector and/or leaking fuel pressure back the fuel tank on shut down.

4. A worn/dieing fuel pump unable to supply fuel as and when required by the ECU

Further info is available for each of the above at the Engine Bay Device Map available here:

http://forums.quattroworld.com/s4s6/msgs/22625.phtml

[rs200]

i thing that you blow off valve have a leak... the rubber inside is maybe too old and they don't want to hold the pressure.

[HMS-S6]

thats what i thought, forgot to list it!

Its a brand new Bailey valve!!

[merlin's S4]

As has already been stated a boost leak pressure test needs to be carried out if you haven't already. This should be your first port of call with any problems such as this and it is generally the bottom intercooler (michelin man) hose that causes the problem. Unfortunately visibly checking the hoses is unlikely to show up any problems.

[HMS-S6]

Yeh i'm waiting for a kit from johhny p (?). Getting fed up with getting nowhere! A boost leak does make sense as the higher the engine speed the less pressure difference as such.

[220bhp]

Mine had a leak on the maf hose where the hetel pipe from the breather enters it, I could not see it until I took it of for inspection it was right in the crease

[HMS-S6]

Glad you found yours, mine is still driving me round the bend!! I'm waiting on a boost check kit before i do anything else, as part of me sees the logic and it does kinda feel like a leak, but is confusing that its better in overboost!

[Key Walshe]

Also check the one going into the throttle body as they wear on the jubilee clip, and also the intercooler/turbo pipe on the joint at the t-piece, they often split there due to the massive heat and repetitive heat cycles. I had a split in both of them, a quick call to Roose for a set of silicone hoses solved it as the ic/turbo pipe is about £170 from Audi iirc, whilst the tb one costs about £25

[topsparky]

Also check the one going into the throttle body as they wear on the jubilee clip, and also the intercooler/turbo pipe on the joint at the t-piece, they often split there due to the massive heat and repetitive heat cycles. I had a split in both of them, a quick call to Roose for a set of silicone hoses solved it as the ic/turbo pipe is about £170 from Audi iirc, whilst the tb one costs about £25

it's an s6 mate roose don't do hoses for the s6
try amber performance

[n32tpd]

same problem

I had the same symptoms when i first got mine, i was reluctant to shell out for new parts incase they werent needed (and couldnt really afford them) and it turned out that the WGFV supplied as a " 100% working " example was slightly different in that the two pipes connecting to it were in effect the wrong way around. Had me stumped for ages and was so simple!! Might be worth double checking part numbers if you are swapping bits from one to the other? Other things i was advised to check (other than air/boost leaks) was that the fuel pump basket was correctly mounted inside the tank, the altitude sensor that hides next to the ecu, and check intercooler as end caps have been known to allow pressure to escape.
I must admit if i'd have followed advice of similar threads on here i'd have sorted it instantly, new N75, new WGFV, new clips on every boost/vacuum hose and if still not cured get the thing properly pressure tested........good luck

[HMS-S6]

Thanks for the tips, i am on my 4th N75 valve, been trying different profiles but am back on a standard H profile again. With regards to the altitude sensor, from what i understand if that were playing up, the boost would be turned down which, it isn't realy!! I have a mechanical gague in the car and it is always around 1 bar or just under. However it has been not so steady sometimes which is why i am wanting to boost check it.

[HMS-S6]

I have just accessed the trick function on the climate readout on my way home. I picked channel 51 which is coolant sensor reading. Now all the way home it read 50 dispite the gauge reading just over 90. Has anyone had this before? Could it be the reason for my poor power???

[merlin's S4]

I have just accessed the trick function on the climate readout on my way home. I picked channel 51 which is coolant sensor reading. Now all the way home it read 50 dispite the gauge reading just over 90. Has anyone had this before? Could it be the reason for my poor power???

It's certainly a possibility. The temp gauge uses the MFTS on the water manifold for it's reading but the ecu uses the temp sender on the back of the head. That's the reading you will have seen from the climate control head. Sounds like this sensor may be faulty so you're probably running rich. Have you got another that you can try? It's possible to swap it without draining the coolant but be quick!

[HMS-S6]

Yeh i have one on the S6 saloon, i'll swap when i get it back from who i lent it to