Checking Fuel Pressure (Low-Pressure) Using Pressure Gauge

1. 1.1  Connect tester > V. A. G 1318 - K-Jetronic Tester  and secure fuel hose using a clamp -1-  or screw-type clamp -2-  .
2. 1.2  The tool setup must be fitted with sealing rings (copper, aluminium, or plastic, etc.) between the individual components. The setup must be fully sealed.
3. 1.3  Start the engine and leave it running at idle speed. Read off the fuel pressure on the pressure gauge. The pressure gauge pointer can oscillate slightly at idle speed. With increased idle speed (accelerator pressed slightly), the pointer deflection calms down. The fuel low-pressure system operates at a fuel pressure of 4.0 to 4.5 bar. 

Courtesy of PORSCHE CARS NORTH AMERICA, INC.

Connection for measuring pressure on the vehicle (similar illustration)

• Engine cold
• Workshop air-conditioned to normal temperature
• Fluctuations may occur if the engine is warm or if the outside temperature is high
• Fully sealed measuring tool setup

1. 2.1  Same tool setup and connection as for measuring the fuel delivery pressure (see above).
2. 2.2  Allow engine to run for a few minutes. Switch off engine. Check the pressure drop. Drop in fuel pressure after "ignition is switched off" must not exceed 1 bar after 1 hour.  Make sure that the tool setup itself does not have any leaks (even the slightest leak). The fuel retaining pressure will decrease extremely rapidly and falsify the measured result with even the tiniest leak.