EXPERT HELP NEEDED!! ABY S2, Voilent jerking and juddering at 4k rpm

[paul.m]

Yesterday when driving into work, I put my foot down and the car revved to 4000rpm, then violently starting juddering (to the point where it shook you in your seat). My first though was coil packs failing as these sorts of problems are usually ignition based.

I spoke to a very knowledgeable friend of mine who said it sounds like the car is detonating, whereby the wastegate is stuck open and full boost is being supplied to the engine constantly. He added if this is the problem then I'd need to be very careful in making sure it doesn't do it again because it will destroy the pistons.

On the drive home again I thought I'd try accelerating hard again just once to see if the problem was still there, I got to 3500rpm and braced for it to do the same thing, and nothing?! It revved cleanly through the rev range and pulled really well Dodgey wastegate perhaps? does anyone have any experience with the behaviour of an ABY engine when the coilpacks are failing?

Thanks in advance for any help!

[Error404]

Wastegate would need to be stuck closed to casue that but afaik it fails safe so cannot happen. You can hear det quite clearly normally, sounds like someone crunching a crisp packet. Although on these engines the knock sensors would pick it up and limit advance and boost to save the engine. Does sounds like a large boost leak or ignition issues to me.

[Sonic]

Yesterday when driving into work, I put my foot down and the car revved to 4000rpm, then violently starting juddering (to the point where it shook you in your seat). My first though was coil packs failing as these sorts of problems are usually ignition based.

Did you still have your foot welded to the bulkhead whilst it was "juddering"?

Sounds like boost cutting.

[GazzaG60]

could be one of many things.

lets work on the theory to start with.

if the wastegate was stuck open then it would constantly bleed off exhaust gases. this would make boost hard to achieve as the gases that go to the turbo are bypasing it.

if the gate was stuck closed then it would overboost at the turbo as the gate opens to attain and maintain the boost pressure.

it could be spark, fuel, or air related. the motronic guru's will help here.

id look at.

knock sensors retarding timing.
lambda probe not allowing clean transition to boost map.
ait too high.
water temps

[paul.m]

Did you still have your foot welded to the bulkhead whilst it was "juddering"?

Sounds like boost cutting.

Well i didn't have the pedal to the floor, it was probably half way down, I was just going to let it wind up along a nice long open straight. When it started juddering I suppose I just let off. It was so violent you couldn't have held your foot in the same position anyway. the more I think about it, the more confused i get

Just went out in it this morning and it was fine.

In response to the water temperature suggestion; I think the thermostat might be open as after driving it home last night (which is about 13 miles) I got home and the temperature gauge was about 55-60 degrees

[Sonic]

13 miles is barely enough time to warm the coolant up, sounds normal to me.

If the cutting is that violent, could be fuel cutting.

Do you have a boost gauge installed?

[Jamo]

Sounds like over boost protection, check for boost leaks

[Le S2 Audi]

I had the same issue and it was a boost leak, one of the small vac pipes had snapped...

Get yourself a boost test kit from Andy P... worth every penny...

Also worth replacing all the small vac pipes...

HTH

[paul.m]

oh good to hear someone else had the same problem (i mean that in a nice way )

I don't currently have a boost gauge fitted going to make up some sort of braket to fit one into the centre air vent me thinks

I've ordered the piece of pipe and hose clips necessary to do the "MarkH" mod, I intend on replacing the boost hoses and auxillary hoses with silocon ones from Roose (unless anyone can offer me new a new Samco set?) Even if the problem arises again, atleast I can eliminate the likely-hood of it being a boost leak.

[Le S2 Audi]

I got a nice Gauge mount Off Ebay.de...

Read this thread; http://www.s2forum.com/forum/showthread.php?t=43074

The buyer I used still has them listed here;

http://cgi.ebay.co.uk/Alu-Zusatzinst...e_Zubeh%C3%B6r

I ordered a black one with Silver OOOO...

HTH

[Rusty]

Sounds like the most common S2 complaint - as Jamo said - over boost protection. Usually due to an air leak on the high pressure side, can also be caused by a mis-reading MAF due to dirt or liquid on the MAF.

Nearly all of us have been here, it's a right pain but once you sort it the car will fly as a boost leak means that even when it runs 'normally' you're still losing power.

AndyP is the man for boost leak test kits.

[Jamo]

I experienced it once when a hose blew off on a dual carriage way ( the day the car was being taken off the road for the engine swap ) it's violent and it doesn't half give you the willies

[driftin jo]

Mine has done this twice before and it was a simple fix as it was the MAF wire connector , just pulled it off and put in back on a few times and it was fine for another six months . I cleaned it properly the last time and it has not done it since (18 months and counting ) .

the first time it did it I checked everything for leaks and found none , spent hours on it and then cleaned the connector and it was fine I could of fixed it in 30 seconds ! I would check this first as you will be pissed off if you spend hours/ days looking for leaks and eventually find it is this.

[newsh]

Yup

http://www.s2forum.com/forum/showthread.php?t=24544

[rj scotty]

Wiggle the MAF connector, it's over-boost protection cutting in on a false alarm. if you have vag com it will show the the over boost protection incident as a fault. BTDT