Running problem, please help...!

[LHD_Kid]

Right, just got back from a weeks trip, meaning the car did huge mileage without many stops (infact about 3500 miles in less than 6 days)
Anyway, all was fine for the first half, and most of the second half...
a few hundred miles from the end of the trip on WOT the car pulls fine, then starts missing and spluttering... If you use 3 quarter throttle it is fine, idles fine... etc...
It happens approaching full boost, but not absolutely every time, maybe 90%.
It is definately not a boost leak, PCV system is fine, new WGFV.
I am wondering if it is a problem with the leads, or maybe the dizzy, but the dizzy is not very old.... I have a new set of leads on the way....
Any ideas? I just need opinions as what to check, which order, etc...
An issue which has arrived at the same time is that the sound from the turbo at full boost has changed, and sounds very..... fluttery..... this happens when the car misses also, almost like external wastegate chatter, or something, but never did this before...
Car does seem low on power. although this might be due to the problem and therefore me never really giving it WOT now...
other things which seem o have appeared (although dont think it is a symptom of the main problem) is that on start up when cold, the engine splutters immediately, then takes a few seconds, maybe 15 to settle, and then when you give a few revs to pull away the engine almost dies (it ha snever stalled, but sounds as if it might)
Sorry to be so long winded, but too much info is better than not enough...
Car has and is being run on 98 RON, and seems ok, MFTS changed, ECU Mihnea remapped... not sure what else to mention ... Intake is via cold air duct and a quickshift cone....
Thanks for any ideas...
Chris

[LHD_Kid]

Anyone...????

Further to the above... at full boost it just kind of coughs a little 2 or 3 times a second, as long as you are not absolutely flooring it it is fine....
Starting problem was worse this morning.... splutters a bit more.... have I lunched the head gasket? Oil and water perfectly clear, not losing any water, not losing any oil...
Still hoping most is caused by leads...
would a faulty coil cause starting problems like this?

[iain1067]

The fluttery sound could be a a shot a diverter valve, but then that probably wouldn't cause, could be a fuel pump on the way out, just a guess, you got vag com yet???


iain

[iain1067]

you checked the spark plugs???? like loose????

[LHD_Kid]

Cors I got VagCom, some nice guy gave it to me, with some cheese..!
DV is only 2 months old (Milltek)
Fuel pump, could be..... hmmmm.....
fluttering does sound like its coming from the front though........

[newsh]

I was wondering loose plugs too.

[LHD_Kid]

Yes, this was the first check I made... all were tight, I didnt remove to look at condition, but they are the correct ones an have done about 6000 miles....
I have read about loose plugs on here, dont want that to happen too...!

[Jon441cc]

Maybe be something to do with fuel filter, id replace it if you havent already.

[S-Express]

Maybe be something to do with fuel filter, id replace it if you havent already.

I agree with that - sounds like a classic fuel starvation problem. which isn't good on a blown motor - can't it cause piston melt down???

[LHD_Kid]

Fuel filter is new, changed about 3000 miles ago...
Might it be an injector problem? With the cold start trouble too, maybe a leaky one for that, with it generally being faulty...?
I don't know....
I will get Vag com on it tomorrow weather being well, I have to wheel the pc and monitor outside as I don't have a laptop....
Will see what happens and come back tomorrow...
Thanks for the help so far...

[UrS4boy]

I suggest that you might want to check out my AAN missing and/or hesitation diagnostic procedures on AudiWorld at:

http://forums.audiworld.com/s4s6/msgs/149788.phtml

It should help you show up the problem. My best guess at this point is a bad coil. But you will need to confirm it isn't plugs or a POS channel, etc.

Good luck.

[newsh]

It should help you show up the problem. My best guess at this point is a bad coil. But you will need to confirm it isn't plugs or a POS channel, etc.

Good luck.

Its a 3B.

[Davidsinclair05]

Could be the cars ecu sending the wrong fuel - air mix try the Maf sensor and the air filter. I have had similar problems and went through numerous solutions till I found the fault, I changed the fuel filter. the hd leads, The dizzy cap, Spark plugs and finally the vacuum pipes. I think that if you have time you should check or change the vacuum pipes at the weekend they might of come loose?

[LHD_Kid]

I replaced all the hoses with Samco, including all of the vacuum hose, with new clips everywhere about 2 months ago... I did go round everything again today to check, but all seemed ok...
Ran VagCom today, no fault codes, so not a sensor problem I am guessing...
I soaked the MAF all day in IPA, cleaned the WGFV (which was new anyway) and very carefully cleaned both sides of the MAF plug... again, all with IPA
Checked the condition of the plugs (correct plugs and under 6000 miles on them) and made sure they were torqued up correctly...
After being parked all day, it started with its usual splutter, but drove a little better, although the hesitation was still there, but at a reduced level, ie not as violent (not that it is very violent, not like overboost protection)
Assuming the plugs themselves are ok, is there any way of checking the coil? I am still waiting for my new set of leads, so might have to wait until I can count them out...
Anyway, if everyone keeps their thinking heads on and has a Eureka moment in the meantime, please let me know.....!
Cheers guys
Chris

[UrS4boy]

Its a 3B.

Okay. Sorry, I must have missed that. Obviously I am used to AANs, etc. and all their lovely inherent (potential or real) ignition problems. 3B and a Hall-sensor distributor and single coil should be easier to track down. (or NOT).

Dave F.