[V8] 2002 A6 Quattro V8 4.2L. Starting problem

[John Zofchak]

Greetings Fellow Subscribers,  I am new to Audi as I have just purchased an
A6, 2002 V8.

It appears to have the potential to be a fantastic car.
Needs new cat. Converters, N80 valve, B1 S1 O2 sensor,  Got an inspection
from Audi for these results.
Car has been driving quite well.  Right up to the point where it suddenly
won't start.
At least it got me home before dying.  Still have check engine light from
the cat.s.
Managed to find a Huge hole in a large vacuum line which Audi missed, got
rid of the after-sucking noise.
After trying to start one could here this vacuum release to atmosphere.
 Cut and replaced hose.
I see I am just the newest person to find incredible fault with a ( so
called )
Factory Service Manual.  For that price it should be more than a picture
book. Bentley should be ashamed.
My fuse panel shows only 3.5 V on several points until cranking then up to
10 V
Including the ECU and the Fuel Pump.

I live very in a very remote area and need better reliability than this.
I have purchased new Davico Catalytic converters, N 80 valve, O2 sensor.
Also got Irridium plugs, A Vortex generator, A K&N air filter.
Was wondering if doing the converters is a DIY job or best left to the
pro's?

Any help on the starting would be greatly appreciated.

Thank you from Windy Top
John