Before troubleshooting, check that there is fuel in the fuel tank, there is no air in the fuel system, the compression in the engine cylinders is within normal limits, the battery is fully charged and the starter turns the engine crankshaft at a sufficient speed. Malfunctions of the electronic control system can only be determined using a special device.
If the fuel lines will be removed, first clean the area around the fuel injectors and fuel line union nuts.
The article was copied from the website: AudiManual