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sprinkles08, ASE Certified Technician
Category: Audi
Satisfied Customers: 22980
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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Audi A8L: Car won't start when hot

Customer Question

Car won't start when hot
Submitted: 2 years ago.
Category: Audi
Expert:  sprinkles08 replied 2 years ago.
Hello and welcome to JustAnswer!
The pr0blem could be quite a few things, especially depending on what it's actually doing.
I'm assuming it cranks but doesn't start. If that's the case then the first step in diagnosing the problem will be to check for fault codes.
If there are no codes setting then I would first suspect vapor lock. When you park a vehicle with the engine hot, the high underhood heat will keep fuel pressure in the rails elevated. If the fuel pump check valve is weak this elevated pressure can cause fuel to push back into the tank, leaving high pressure vapor in the rails instead of liquid fuel and it causes a hard restart when hot.