System Pressure

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.
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).
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.

NOTE: When vacuum hose is disconnected from fuel pressure regulator, mixture is enriched. DO NOT operate engine for longer than necessary with hose disconnected, as oxygen sensor limits may be exceeded, causing a code to set.
Turn off all electrical accessories. Run engine at idle (this automatically interrupts output DTM). Ensure radiator cooling fan is not running.
Difference in fuel pressure with vacuum hose connected and disconnected at fuel pressure regulator should be about 7.3 psi (0.5 kg/cm² ). If difference is as specified, system is okay. If difference is not as specified, check for faulty vacuum hose or blocked vacuum port at intake manifold. Repair or replace as necessary. If hose and vacuum port are okay, replace fuel pressure regulator.