a6 2.7t.... help needed (s4 engine)

[audi-a6]

Hey.......
i have an a6 2.7t, same engine as the s4, did originally post this in the a6 forum, but they recommend posting here.....

okay, straight to the point....... 1st ptoblem, when im driving normally i take my foot off the pedal and the car feels like some has just drove up my A$se! Like a shunt. Does it all the time(except for the first 5 minutes from cold) any ideas??


2nd problem, sometimes my boost drops, mostly to 0.3/0.4 bar (currently running 1.1 from a re-map) it does under NO specific load, sometimes if i floor it, sometimes i can be just driving under load (apx .8 bar) then all of a suddeni can hear the bovs dump and it will drop to 0 and get the shunt back, as if i took my foot off the pedal.

any help would be great

[Bradderz_1988]

Failing maf possibly ??

Or if when you let off check the tranny mounts if these have seen there days the you may have some slack in the tranny causing it to shunt when letting off !!

[audi-a6]

na, cant be mounts, as does not do it when cold

maf? iv never know a maf to do that

[Bradderz_1988]

If a maf suddenly cuts the fuel it will cause the car to shunt.

You scanned it with vagcom ??

[audi-a6]

na, cant be mounts, as does not do it when cold

maf? iv never know a maf to do that

had it scanned a while ago, nothing came up

[Blue_Thunder]

I have s shunt like this. I've changed virtually everything and still not solved it. New flywheel, new engine mounts, new gearbox mounts, snub mount, DTS and a centre diff.
Next thing is to change the gearbox and rear diff.

[audi-a6]

did you have boost problems as well?

[audi-a6]

Also why have you only changed mechanical parts and not electronic ??

[aragorn]

The boost dumping means the ECU thinks something is wrong. That may be due to a crappy remap, or it may be due to leak or a faulty sensor. Vagcom scan (not some ****ty code reader, use vagcom) should be the first port of call.

Every B5 i've owned has eventually developed a shunt like you describe. I notice it most at motorway speeds, and i found that you let off the throttle, and there would be a momentary delay then a thunk. I always imagined it felt like a large heavy steel ball was rolling around the boot and had come up hard against the back of the seats.

Its most commongly caused by the engine mountings (and possibly prop or rear diff mountings on a quattro). Under load the engine obviously twists against its mounts and when you remove load the mounts relax, then you transition into overrun and the mounts twist up the other direction. When the mounts wear out, they become slack, allowing the engine to effectively flop loosely between the two extremes, and this floppyness exhibits as a shunt feeling as the engine/transmission assembly comes up hard against the end of the floppyness.

The mounts in the missus Quattro are really bad and it will do it both when lifting off and reapplying power again.

Worst case it could be play in the Prop/CV's or Diffs themselves, but as most of these cars are pushing on a bit now, i'd defo look at getting the mountings replaced and see how that goes.

[audi-a6]

I know it's not the mounts or anything like that as it will shunt if I'm not under load. Eg, going down a road at 30mph constant speed, then just take my foot off to slow down, it shunts it's got to be electronic related....... So if any one has a vag com and are local to Bournemouth, it would be a great help

[audi-a6]

also, if i take my foot off super quickly, it wont do it, the slower i take my foot off the harder it shunts, its like the engine tries to run on, then quickly changing its mind.....

[Sulli79]

I know it's not the mounts or anything like that as it will shunt if I'm not under load. Eg, going down a road at 30mph constant speed, then just take my foot off to slow down, it shunts it's got to be electronic related....... So if any one has a vag com and are local to Bournemouth, it would be a great help

Does sound very similar to mounts, though not a 2.7 mine would do the exact same thing, if i had my hand on the gear lever I could feel the whole drive line move what felt about an inch, replaced snub mount and both engine mounts and it improved dramatically, will be replacing all the rest of the mounts now as car is off the road at the moment.

[audi-a6]

I have no movement atall in my gear stick

[Airfix]

I have no movement atall in my gear stick

i`d get that sorted asap !!!

[aragorn]

Perhaps stick your query over on the B5 S4 section of AudiSRS.com theres a lot more 2.7T owners over there, so a bit more knowledge floating around.

[audi-a6]

Yeah will give a try, the other reason why I don't think it's mounts is because it don't do it when cold :-s

[Blue_Thunder]

Also why have you only changed mechanical parts and not electronic ??

No boost problems on mine. Electrical faults couldn't cause the shunt in mine. It is definitely mechanical.

[audi-a6]

No boost problems on mine. Electrical faults couldn't cause the shunt in mine. It is definitely mechanical.

Does yours do it from cold?

[Blue_Thunder]

All the time.

[audi-a6]

See, mine don't do it when cold, another reason I don't think it's mounts, I'm starting to wounder if the boost problem and the shunt problem are linked to the same part :-s

[Blue_Thunder]

I tell a lie... Mine doesn't do it when cold either! I've had this problem for as long as I can remember and I'd never noticed!
I guess after a while I've adapted the way I drive to minimise the effect.

The only other person I wa aware of that had the same problems on the forum had his gearbox replaced and it got rid of his 'kangarooing'.

[aragorn]

If its transmission related, perhaps the thicker (cold) oil has a dampening effect?

[audi-a6]

mmm, i see what you mean........... but i just cant put it down to that.......... as like i said above, the slower i take my foot off the harder it will shunt....... where if it was mounts, box ect it would do the opposite ie take your foot of quickly it would shunt, but this is not the case

[audi-a6]

what about flywheel. Could that cause the shunt?


Also any one got any ideas for my other problem with the boost, as it has got worse, if im in 6th gear doing say around 70mph and i put the throttle on about 50% the boost drops to 0 and does the shunt as described above, then wont boost over 0.4bar untill i turn the engine off then back on again.

[Blue_Thunder]

Sounds like you've got a bad boost leak. Get it tested.

I thought a knackered flywheel could have been the culprit, but as mentioned, I swapped mine for a new LWFW and it's still just as bad.

[Bradderz_1988]

Have you checked for any fault codes with vagcom as that will put you in some sort of direction as to where to look at and also using measuring blocks to see what the maf is reading when faulting ?? Your boosting fault is more than likely electrical and your shunt may also be electrical as when I had a failing maf when the maf was cutting fuel it would appear as if I had just hit a brick wall !!

[audi-a6]

that would make a lot of sense, will order a vagcom today,

[audi-a6]

okay, so 5 weeks on and many pounds spent, still no joy, had another remap done on a new ecu, got new thermostat and cambelt, full service, plus other bits inc n75 valve, but still no joy and still throwing code 17963 but all my limits have been removed, so how can it throw this code, it mainly does it at higher speed, ie accelerating from 60 in 6th gear, take foot of gentley and then boost cuts, have checked for boost leaks, so could it be map or maf sensor?

[adidasandy]

code 17963 = Maximun charge
So the car is over boosting and going into limp mode.
Now on the TDI Golfs this problem happens alot as the turbos have Variable Geometry Turbo (VGT) which get jammed causing it to over boost. I have repaired many of these but not sure if your turbo has the same set up. Have you checked your actuators?

[audi-a6]

no not yet, but according to my gauge i never over boost and even if i was, it shouldnt matter as i have no limits set in the ecu

[aragorn]

You've still not had a boost leak test have you?

Moreover, you've obviously not taken it anywhere competent to have the remap done either, or it would have been sorted then, rather than them just turning off the safety features. Luckily for you, it seems the ECU is smarter than whoever has been pissing around with it.

[audi-a6]

what do you mean? i have tested for leaks and done a new map and removed limits to see if it still does the problem, which it does, also tried a standard ecu and still does it, therefore its not the map, thats why i think its a dodgy sensor

[murran]

that code is Boost Pressure Control: Upper Limit Exceeded.
as you yourself pointed out..... if theyve mapped no limits into it how can it come up with this code?

boosting in the higher gears midrange i bet its hitting the fuel cut, or opening the recirc valves too early as you come off the throttle. take it elsewhere for the map.

[audi-a6]

but the guy who done my car has done loads of these with out no problems.......... and obviously i dont want to spend more money on another re-map to find it still does the same

[aragorn]

My point is simple: if the guy actually knows what he was doing, he wouldnt have sent you away with a broken car.

[audi-a6]

yeah, i see where your coming from, but what if it was broken before. i was only running .4 bar, there for not boosting high enough to cause the fault and with saying that, the car had been mapped before i got it, as the map file was encrypted, yet was running low boost, so there must have been a fault before this guy touched it............... i got work from something, so would you say its unlikely to be maf or map sensor?

[audi-a6]

also, dont know if its the same problem, but also SOMETIMES throws code 17965 and ross tech states for both codes "Charger Pressure Control defective"

[audi-a6]

still got this problem, change maf, map and n75, no boost leaks, tested my ecu in another car and it doesnt do it, its really puzzled me, what else could it be, just to re-cap, the codes are 17964 and 17965 one is negative deviation the other is positive deviation???

[audi-a6]

im at whits end now, i can not solve this problem, its really starting to do my head in, i think im coming to the point where i have to sell, as this is 1 of 3 problems now, that i can not fix or find out even what is causing the problems.... :-(

[audi-a6]

could it be this

charge pressure controll hose?

[Blue_Thunder]

A pressure test would reveal a leak in that hose.

Do you still think the shunt isn't mechanical? As mentioned, it does sound like mine. I'm swapping my gearbox out the lsat week in May. Will report back then.

[Blue_Thunder]

Have you checked your DV's are holding pressure?

[audi-a6]

boost leak test doen, all was fine, dv's are fine and i think the shunting is my rear diff as if i pull away quickly while turning it sounds like a load of chains rattling around............ also my mate done a vag com run and said all looked okay apart from the vag com was reading a different temp to what the dash gauge was running and said, although im hitting a full 1.2 bar of boost, the torque is quite flat in some gears, he said it feels like its holding back???