How to check knock sensors, monitor knock?

[20Vcqdriver]

Hi Rocco, I was thinking of selling the coupe.. This is the Avant, the car boosts fine to 1.5 Bar with homefried ECU untill you run it hard through the gears, then boost drops to 0.7 Bar, if you drive it easy for a while or switch off and back on again its fine till you drive it hard again, very frustrating!

HAd very similar issue with mine, but worse and found the front knock sensor too loose, a re-tighten sorted mine but took a while to figure out as it never brought up a fault code!

[Rusty]

I don't think the knock sensors limit boost

Sounds like altitude sensor John, located in the passenger side front footwell, designed to reduce boost

[Rocco]

I don't think the knock sensors limit boost

Sounds like altitude sensor John, located in the passenger side front footwell, designed to reduce boost

+1 as i´ve said

[newsh]

Interesting, thanks for that Rocco, I'll check with Vagcom to see if its reading a weird altitude. Its like a switch, just drops from 21psi to 10 psi immediately after a quick run.

[newsh]

I don't think the knock sensors limit boost

Sounds like altitude sensor John, located in the passenger side front footwell, designed to reduce boost

So many people have said that they've had similar problems with knock sensors though I've been asking this question for a few months and no one has mentioned the Alt sensor before

[Rusty]

Speak to s2central for a graph (or check out sjm), the altitude sensor gives out a voltage that the ECU uses to knock back boost and prevent over spooling the turbo (turbos spool to gauge pressure so you get a larger pressure difference over the compressor at altitude). Could just unplug it and see what happens, not sure what the default value is. Same goes for the knock sensors, no signal will result in a base value being applied.

[UrS4boy]

I don't think the knock sensors limit boost

Well, no, the knock sensors do NOT limit boost. However, the ECU does, when it does not get a "happy engine" signal from the G61 and/or G66 knock sensors, as discussed here (for an AAN but much the same for an ABY or ADU):

http://forums.quattroworld.com/s4s6/msgs/21047.phtml

If that doesn't provide any joy, this post about the F96 altitude sensor explains why the boost might be limited by a faulty F96:

http://forums.quattroworld.com/s4s6/msgs/21892.phtml

More general info about the AAN (and ABY and ADU) engine bay devices that the ECU uses to control fuel and boost, is found here:

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

[newsh]

Thanks, I have done some reading!

[newsh]

You build a frickin' amazing 3B coupe, solve all the problems, and then decide to flog it and start again with an Avant?

Change "flog" to destroy and the story starts to sound familiar Sorry this doesn't help you at all

Well after seeing David's car today I got all misty eyed and I've changed the sunroof in the coupe, got both the broken bumpers off too just thought I'd make a start on it and ended up doing the job.. Seriously knackered now though

[s2driveruk]

it wasnt even washed and waxed

I reckon we should start some kind of S2 Samaritans Group - if you close to ending it (the relationship with an S2/Rs2 of any flavour) then someone close by has to immediately rock up in their car and talk them round

[newsh]

[Rusty]

Can't cope with your impure thoughts about the darkside, worried that you'll end up like Jamo? Call 0800 'I don't want a hearse' and speak to a friendly ear.

[220bhp]

John l think you should hang on to the coupe they are the ultimate in looks and will always command a better price.
If audi had made an rs2 coupe it would IMO be worth much more than the rs2 avant. I have an s6 avant , which I think is great and it has never given me any problems. But when I look at the coupe it is just so cool, but believe me it has given me some problems, not least the knock sensor problem, which took me a long time to diagnose.
The car had this problem when I first bought it, it would never pull like my s6 which was alot heaver.I replaced every sensor and every boost hose,all made a tiny difference,but it never pulled like the s6 until I replaced the front knock sensor, which was showing signs of age.the car ran great after that,[until the next problem came along] but there you go.

[Bram]

Can't you just check knock sensors by running the engine idle and hit the block with a little hammer and see if the RPM's are dropping or the engine starts running differently for a second? I tried that on mine and it worked fine

[newsh]

Guys its true, Coupes rule in the looks dept and I've fallen back in love with it this weekend but I still want to get the Avant running properly and at the moment it goes really well till you floor it through the gears and then suddenly you've only got 10psi of boost! a few minutes later you've got 20 again

Bram, I'm not so worried that the knock sensor is working I think it might be working too well and triggering off the noise of a normal engine. This would mean the ecu was being told there was knock when there wasn't.

The other thing I'm wondering about is the TPS and if it has a dead spot