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Discussion Starter #1 (Edited)
I need some help regarding my 2002 A6. Recently it suddenly stalled out in perfectly good weather but after we'd had a long period of almost daily heavy rains. It restarted a 4-5 times briefly but stalled, now permanently.
Also, since the event, after turning the ignition to ON, after about a 5 second delay, the radiator cooling fans come ON HIGH.

Suspecting fuel (because it did fire-up a few times)
I checked the following:
Vacuum lines - all AOK (new silicone lines)
Fuel pump fuse - OK
Terminal 30 of FP relay socket 13V
Fuel Pump fuse socket supply side 3.6V
Jumpered the Terminal 30 of Fuel Pump relay socket to fuel pump - Fuel Pump RUNS BUT Engine does not fire.
Replaced fuel pump relay - still 3.6V at supply side of fuse, no run no start.

Other things done:
Roof drains - clear.
Firewall plenum - clear (removed battery & its tray and manually cleaned/ checked the drain)
E-Box - clear & dry and all relays check out w/ digital VOM. BUT the adhesive insulation under the E-Box is wet and perished.
Cabin air intake tray (the elevated part around the opening) had water and had clearly overflowed into the opening. Like the E-Box, the adhesive insulation was soaked and perished.
Passenger side carpet had free water on the carpet but it was largely beaded up on the surface rather than soaked in.
A ground point attachment to the left of the cabin air intake shows a lot of mineralization and start of corrosion.

So here are the questions:
What specific sudden event could cause the voltage drop from the fuel pump relay?
What other components are switched / serviced / actuated by the fuel pump relay?
What other component could reasonably be affected by or fail in relation to the voltage drop?


It seems to me to be either something shunting current from the FP relay output, or the corrosion of the supply line to the FP fuel pump fuse base. Or another fuel or fire component is also not actuating as a result of the voltage drop, such as cam or crank sensors, ignition lockout, security lockout.

Any help would be appreciated. Thanks.
 

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Discussion Starter #2 (Edited)
Update:
The following was done, all without solving the problem
Crankshaft position (Engine speed) sensor replaced.
Coolant temperature sensor changed.
Timing belt is intact, but I can't tell if jumped a tooth or two or more.
The voltage at the fuel pump fuse is still 3.6V with the original and new relays.
The fuel pump runs when jumpered with 12v directly.
The engine does not sounds like it wants fire either.

Could someone please tell me what functions would lock out the fuel and ignition?
 
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