EDIT FIXED!!
Car: 2004 Convertible A4, 20,000 miles. Very nice and clean car, completely stock.

Concern: Misfire at all times, worse when accelerating and is very violent under heavy acceleration where it wont move the car faster at all. Misfire is in bank 1 only. The only DTC is P0300 for misfire. With a Tech-2, cylinders 5 and 7 are the major misfires but cyl 1 and 3 misfire about 1/2 as much. Fuel trim shows -10% for bank 1.

Things I have checked:

Fuel pressure... Checks at 50 PSI at the rail and holds.

Fuel Injectors... All measure 12 ohms and have power at their connector's.

Coil Packs... Swapped coil packs from side to side and same problem.

Plugs and Wires... Plugs and wires are good, lot of carbon on cyl 5 and 7.

Grounds... I've checked the ground on the back of bank 1 cyl head and the ground at the frame on the drivers side, all OK.

I'd have to say this is making my head spin. If it was fuel pressure related or a short in the coil/injector harness it would make all cylinders equally skip at least in bank 1 (I think). The car is too nice and low mile for head gasket or internal engine failure plus there are no abnormal noises.

Next I will check the exhaust. Maybe there is a restriction in bank one (cat). Please help .

 

That fuel pressure is low. While it may not be your issue, it certainly needs to be investigated.

 

Did you run OBDII diag for codes? They will tell you what plug misfires and then you can begin to solve.

 

Fuel pressure is within spec per GM SI. 60 PSI upon Key On, 50-55 steady after rail is primed.

No offense, but please read my post before commenting. It clearly states DTC P0300 is the only code present and Cyl 5 and 7 are a steady misfire where 1 and 3 are intermittent, more present upon acceleration.

 

All the misfires are on the driver's side---What can happen one cylinder can have a mech issue & it will eventually foul all the plugs on that side
I would suspect a broken valve spring--take off the driver's side valve cover----also a compresseion check of that side as well--

 

There is a wiring harness on the back of the cylinder head that feeds the injectors that's known to get chaffed and short the injectors. Do a search on it, I seem to recall some pics.

 

I'll do a compression check and post the results.

I did some research before posting and did find several posts on this. That seems to be more common when the fuse for bank 1 blows or all cylinders are equally effected. The harness was not rubbing against the back side of the engine (brackets, heads, etc.). That doesn't mean there is not an issue I can not see. Will still keep this in mind.

 

Maybe they are shorting together making the injectors fire weakly or not at all when stretched-just becuase they are not shorting to ground does not mean they aren't touching each other. I would look VERY closely in that area.

 

Found the problem today. The primary cat was clogged (not the baby pup cat) on the drivers side. I removed the exhaust, and fortunately an aftermarket H-pipe was installed so I was able to remove the second half of the mid-pipe to peak at the cat. Sure enough there was some cat particles sitting in the pipe. Slapped a new mid-pipe in and she fired up and ran smooth.

Very odd condition and I imagine the cat was only partially clogged. Both secondary 02 sensors looked healthy in the scan tool, indicating a properly operating cat. Oh well... on to the next.