Fuel-related reasons why an AAN takes longer than normal to start
01-18-2008, 11:42 AM
#1
AudiWorld Super User
Thread Starter
Fuel-related reasons why an AAN takes longer than normal to start
I started a 119k km 93 S4 yesterday at a dealership. It took way too many cranks to fire for my liking. I have suggested to the dealer that the potential reasons for this include:
1. Fuel pump in general is dieing. Long cranking times is about all the warning you get before the pump dies. This can/will strand you at the side of the road and = $$$ because of towing, strange dealership, etc. (BTDT).
2. Fuel pump is fine per se but the internal check valve is dead. Annoying but not fatal, i.e. car runs fine after start up.
3. Fuel pressure regulator is dieing, allowing fuel to drain from the fuel rail back to the tank when the car is off instead of holding pressure in the fuel rail. As a result, it needs a few extra cranks (time) to fill the fuel rail and get it back to the 4 Bar differential pressure, e.g. 56 psi at start-up.
4. Fuel pressure regulator is fine but there is a vacuum hose leak that allows the FPR to let fuel drain back to the tank. This is just an idea. Not really sure if its really possible or not. (any BTDTs out there??)
5. Something else that I haven't thought of. (Add your thoughts to the thread. Keep them to fuel-related as opposed to ignition-related).
Dave F.
1. Fuel pump in general is dieing. Long cranking times is about all the warning you get before the pump dies. This can/will strand you at the side of the road and = $$$ because of towing, strange dealership, etc. (BTDT).
2. Fuel pump is fine per se but the internal check valve is dead. Annoying but not fatal, i.e. car runs fine after start up.
3. Fuel pressure regulator is dieing, allowing fuel to drain from the fuel rail back to the tank when the car is off instead of holding pressure in the fuel rail. As a result, it needs a few extra cranks (time) to fill the fuel rail and get it back to the 4 Bar differential pressure, e.g. 56 psi at start-up.
4. Fuel pressure regulator is fine but there is a vacuum hose leak that allows the FPR to let fuel drain back to the tank. This is just an idea. Not really sure if its really possible or not. (any BTDTs out there??)
5. Something else that I haven't thought of. (Add your thoughts to the thread. Keep them to fuel-related as opposed to ignition-related).
Dave F.
01-18-2008, 12:34 PM
#3
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CrankPS and or CSS
Old ones need a few cranks to get to min voltage to tell the ECU/POS to fire.. Mine did this.
I personally think I have either #2 or #4 wrong with my car as the PO changed the fuel pump with an aftermarket version or since my cruise control wont hold speed (slowly slows down) I have a slight vacuum leak.
I personally think I have either #2 or #4 wrong with my car as the PO changed the fuel pump with an aftermarket version or since my cruise control wont hold speed (slowly slows down) I have a slight vacuum leak.
