1994 Audi 90 CS QuattroFACTORY OEM SERVICE PROCEDURE

System Pressure

  1. Ensure fuse No. 13 (fuse No. 17 on 100 model) is okay, fuel filter is in good condition and battery voltage is 12 volts minimum. See ELECTRICAL COMPONENT LOCATIONS  table at beginning of article. Connect Pressure Gauge (VAG 1318) between fuel supply line and fuel rail. Open pressure gauge lever. Disconnect vacuum hose from fuel pressure regulator. Plug open end of vacuum hose.
  2. Initiate OUTPUT DTM. See G - TESTS W/ CODES article in the ENGINE PERFORMANCE Section. Activate fuel pump relay. If fuel pump does not operate, check fuel pump. See FUEL DELIVERY. If fuel pump operates, check fuel pressure. If fuel pressure is 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, go to step 4).
  3. If fuel pressure is not as specified, replace fuel pressure regulator and recheck pressure. If fuel pressure is less than specified, check for damaged fuel pump or restricted fuel supply line. If fuel pressure exceeds specification, check for restricted fuel return line.
    WARNING: Excessive fuel pressure may rupture fuel pressure regulator diaphragm, causing fuel to enter engine through vacuum hose. This could result in an explosion.
Factory Service Tools

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Disclosure: Verified tool recommendations may earn an affiliate commission at no cost to you.

Shop Manual-Ready ToolsCompare Repair QuoteQuote Shield Pro

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.