Low boost

[shaun5]

I have recently bought a S6 Auto and the car doesn't go like it should, my 80 TDI seems faster The car only shows 1.4-5 bar on the computer so 0.4-5 bar

I was luck enough to get Error/Alex to put VAG.COM on it at ADI and only one fault came up (idle switch, which he cleared and didn't come back)

There was a figure that wasn't moving on the laptop which Alex thought was a boost leak on a small air pipe / map sensor in ECU? I carried out a mitivac test and it held pressure ok, I did tighten all the small pipes that connect to the inlet manifold.

Next thought was ECU fault, ive swapped it with one I know is ok and no difference

Can someone please confirm what an S6 Auto should boost to? would there possibly be a fault with the Auto ECU causing it not to boost? or can someone give me some advise on what to check next.

Car has only done 116k with good history, it doesn't smoke/use oil or water, its got to be a sensor surely?

[Error404]

Sorry to hear its still causing you a paint in the butt Shaun.
Just to clarify me and TimE-J looked at the measuring block in Vagcom for the MAP sensor and it was totally static when we revved the engine which didn't seem right.
We also check the N75 was plugged in. Perhaps there is a fault there. I couldn't do an output test as I only have the free version of VCDS.
AFAIK the S6 should boost up to around 1.3 bar on overboost, same as ABY?

[UrS4boy]

UrS4/S6 Moisture trap info

0.4 or 0.5 Bar above atmospheric = spring pressure = either the ECU is not getting boost signal from the intake manifold or the N75 is not connected to the ECU or the N75 has failed.

More info about those devices here (click on the links in the diagram):

http://members.shaw.ca/speedtek/UrS%20Engine%20Bay%20Device%20Map.html

[UrS4boy]

C4 UrS diagnostic ports and output tests

I couldn't do an output test as I only have the free version of VCDS.

To do an output test on an AAN (e.g. to check the N75), all you need is a bent paper clip:

http://www.sjmautotechnik.com/trouble_shooting/ecuf20v.html#outs4

http://forums.quattroworld.com/s4s6/msgs/90409.phtml

[S2central.net]

Paper clip trick works on 3B and ABY too!

[shaun5]

Thanks for the links, I will try and do the tests one evening when its not raining or maybe i'll just swap the N75 valve with one I know is good

[shaun5]

N75 valve changed and I now have a car that boosts only went on a short test drive and the car was still cold so I didn't give it the full beans but I did see the dash show 1.7
What a difference it has made, I was starting to think the Auto was the VERY poor relation to the manual. Next job is to change the auto box oil and filter.

[Error404]

Result! glad its sorted Shaun

[shaun5]

ive had a few good results tonight changed the N75 last night, took the car to the farm tonight for someone look at the air con, found a loose pipe so hopefully tighten that and i'll have working climate .
Car wasn't right on the drive up so i was a bit demoralised, on the way home i thought i'd disconnect the N75, upon opening the bonnet i saw it wasn't connected car was running and when i put the connector on i heard it click. i only had half a mile to home but when i gave it some, it boosted to 1.7 (might go higher but i didn't have time to take it on a longer drive)
Got lots of other little jobs to do to it but im getting there now. Can anyone confirm i need to remove the front subframe to do the sump gasket?

[UrS4boy]

Car wasn't right on the drive up so i was a bit demoralised, on the way home i thought i'd disconnect the N75, upon opening the bonnet i saw it wasn't connected

Got lots of other little jobs to do to it but im getting there now. Can anyone confirm i need to remove the front subframe to do the sump gasket?

Disconnecting the N75 is another way to achieve "valet" or "wife" mode.

To remove the sump to do the gasket, you need to *drop* the subframe down on its mounting bolts but you don't have to remove it from the car (and disconnect the transmission mounts, etc). Support the tail of the transmission to take some of the load as you drop the subframe at bit.

[K Simmonds]

You don't need to remove the front subframe completly to get the sump off, loosen the rear two bolts half way the take the front two out, you can then easily remove the sump.

Obviously this is with the car suported properly using axle stands at either side on the jacking points, level surface etc etc etc, safety first. Or if your lucky a lift

Got to do mine again very soon My own fault for using a duff windage tray.

[shaun5]

cool, thank guys

[shaun5]

can anyone tell me the difference between these part numbers

4A0 511 249 OR
4A0 511 247B

what is the difference? they look exactly the same, the only thing is in ETKA it says about 8 tooth!!!! my car is a S6 estate 2.2t "P" reg 1996

[pasbogdan]

Sorry to hear its still causing you a paint in the butt Shaun.
Just to clarify me and TimE-J looked at the measuring block in Vagcom for the MAP sensor and it was totally static when we revved the engine which didn't seem right.
We also check the N75 was plugged in. Perhaps there is a fault there. I couldn't do an output test as I only have the free version of VCDS.
AFAIK the S6 should boost up to around 1.3 bar on overboost, same as ABY?

What was the group where you looked at map?

[UrS4boy]

can anyone tell me the difference between these part numbers
4A0 511 249 OR
4A0 511 247B
what is the difference? they look exactly the same, the only thing is in ETKA it says about 8 tooth!!!! my car is a S6 estate 2.2t "P" reg 1996

Come on. This is a low boost thread not a rear suspension thread. Bump your other thread again and kill the post above.