volvopentaman

Clear the trouble codes, first swap the coil from another cylinder, and see if the problem follows with the coil.

Watch not to break the coil, when you take it out (shouldn't be too hard if you just swapped plugs).

If this is not the problem, then swap an injector in the same manner.

Projekt 8E

I did have the recall done nearly 3 years ago. I'll add swapping the ignition coil to the list. This weekend I am going to replace all vacuum lines and inspect the arms that control the flaps for adjusting air flow in the intake manifold.

Mister Bally

I had the coil packs swapped for the "campaign" 26 months ago. A year later, one of the new ones went bad. No warranty as the car was long past OEM coverage and I don't believ in extended warranties. New coil pack was twenty bucks or so.

MP4.2+6.0

Just as an FYI, the last two are both cylinder 5 I think. The other ones in the earlier part of the list all seem to loop back to all the different motor and torque mount.

I think OP now has a decent action plan for next steps, and fixes/diagnostics.

Bangerla

Doesnt the second fuel pump kick in above 3500 rpm? Maybe the pump is dead, and it is running out of fuel.

Projekt 8E

It does kick in. I thought I read 3K RPM, but either way, it is on the list. I have a fuel pump on the shelf here just in case. I was leaning that way at first, but the community has brought up other options that seem slightly more relevant to start with. If my planned steps (all vacuum lines and intake arms for internal flaps) don't rectify it, I think the fuel pump will take precedence.

mishar

Have you checked fuel pump fuses? That would be easy fix.

Flaps links can't cause this, but it won't hurt checking them.

Plugs and coils would cause misfiring and you would have that code.

There is fuel pressure regulator too. If I remember well one type of fuel filters has it integrated. Do you have filter with 2 or 3 pipes?

Projekt 8E

I haven't checked the fuses for the pumps because when I was logging the car, I monitored the pumps via vag com. Obviously the passenger side one works because the car runs. The driver's side pump was reporting through vag com to be turning on, but obviously I can't tell how effectively it is pumping without measuring it by powering it independently and disconnecting the fuel rail at the engine.

From everything I have read about the intake manifold and the internal flaps for adjusting air flow, if they aren't functioning correctly, or worst case scenario, one of them had seized at one point and broken the plastic key on the end of the rod, then the torque curve is directly affected. I know your theory is that the motor is cutting back because of the one cylinder, but I just haven't come across any evidence of that being the case. I'm not discounting it as a possibility though.

I will be switching coils around tonight though. I need to get some screws though from Audi that hold the ignition coil rail in place. Last time when I changed the plugs, I had to use an easy out to get the screws out as the last person to remove them (Audi) tore them up nicely.

My fuel filter is 1 in and one out.

Bangerla

You might want to look and see where #5 is on the fuel rail. If it is last on the fuel rail, it might be getting low pressure if the second pump isnt running, causing errors etc.

Projekt 8E

That's a possibility. Not my motor, but I would assume the cylinder numbers wouldn't change.

<img src="http://www.audi.tigran.lv/images/audi_v8_engine_cylinder_location.gif">