1994 Audi 90 CS QuattroFACTORY OEM SERVICE PROCEDURE

Fuel Pressure Test

  1. Ensure ignition is off. Slowly remove fuel filler cap. Wrap a cloth around service port on fuel rail. Slowly loosen service port cap. Install fuel pressure gauge at service port. Disconnect differential pressure regulator harness connector.
  2. With transmission in Neutral, start engine and let it run. System fuel pressure should be 55-61 psi (3.8-4.2 kg/cm2 ) on Cabriolet and 90 models; 89-96 psi (6.3-6.7 kg/cm2 ) on 100 models. If system fuel pressure is lower than specification, perform fuel volume check. See FUEL VOLUME CHECK. If fuel volume is okay, replace fuel pressure regulator.
  3. If fuel pressure is greater than specification, remove return hose from pressure regulator and place in a container. Repeat test. If system pressure is okay, check for restricted fuel return line. If pressure is incorrect, replace fuel pressure regulator.
  4. Turn ignition off. Wait 10 minutes. Residual pressure should be 44 psi (3.1 kg/cm2 ) on Cabriolet and 90 models; 48 psi (3.4 kg/cm2 ) on 100 models. After 20 minutes, residual pressure should be 32 psi (2.2 kg/cm2 ) on Cabriolet and 90 models; 46 psi (3.2 kg/cm2 ) on 100 models.
  5. If system fuel pressure is low, check fuel pump check valve, sensor plate free play, fuel distributor "O" rings and seats. Replace if necessary. If these components are okay, replace fuel pressure regulator.
Factory Service Tools

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.