A6 2.7t running lumpy

[gazza57]

Morning all!

Started my 2.7t A6 on saturday, running lumpy like one cylinder not firing, stopped it, left it 15 minutes still the same, left it a further 15 minutes, still the same
Left it overnight, started it in the morning, no misfire, running lovely, drove it until completely warm and returned still running fine ever since.
Scanned it for fault codes showed pot number 4 wasn't firing.
Have driven it 30 miles still with no misfire since, I suspect it's a coil pack, but haven't ruled out injector or spark plug.
If it is the coil pack I shall renew the six as the car has done 120k, anyone out there got any ideas how I may be able to confirm exactly if it is the coil pack or whether I may have injector/spark plug problems, I will also replace the plugs, but as the coils are £50 each, I want to be reasonably sure they're the problem before shelling out £300!
Thanks
Gazza57

[adamss24]

If a coil fails, the others soon follow. I know it sounds expensive but thats the way is. Keep tabs on it, if its still manifest after a while or it worsens, then maybe its time for a propper service. If it does not do anymore, then its your gain, just throw some injector cleaner in the tank and forget about it.

[gazza57]

Thanks adamss24,
I have decided to replace all six coil packs and the spark plugs, if the problem still persists then I can be reasonably sure it's the injector, I will probably put some injector cleaner in at the next fill up anyway.
Any preferred cleaner for the injectors?
Thanks for your help
Gazza57

[gazza57]

Disaster!

Have just replaced all six coil packs, ran smoothly for five days, now misfiring again!
Scanner showed pot 4 misfire.
It has had new plugs,new coil packs and we have swapped over two injectors, scanner still says pot 4 misfire.
Compression test shows all pots good.
ECU signals look good, the suspicion now is some sort of air leak on the inlet manifold somewhere but why only intermittently?

Add to that a blocked heater matrix which I suspect means dash out ???? and that tops a thoroughly awful week.

[gazza57]

Further developments on the misfire, I replaced all six coil packs and plugs and everything appeared to be fine, then I developed another fault with the heater, no heat, in the course of trying to fix that the misfire has returned.
I am now focused on trying to sort out just the misfire, now the scanner showed pot 4 misfire, injectors swapped over, still the same, pot 4 misfire.
Replace gasket on inlet side, still a misfire but now Pot 5?

We have now traced the fault to the earth wire which runs to coil pack 5 , there appears to be no earth or a bad earth on it.
I'm told there are three wires to each coil pack, two pulse wires and an earth wire.
We appear to have lost this earth connection, however I can't get hold of any wiring diagrams to see where the earth wires go.
They certainly don't go back to the ECU I am beginning to lose the will to live!!!!!!!!
Gazza57