Most shops test Yamaha HPDI injectors as if they were port injectors. However, they are not, these injectors operate more like gasoline direct injection (GDI) systems. On a Yamaha HPDI (High-Pressure Direct Injection) outboard engine, the fuel pressure at the injector is significantly higher than conventional systems, but not as extreme as GDI or Piezo injectors.
Yamaha HPDI Injector Fuel Pressure:
-
Fuel rail (injector) pressure: Approximately 700 PSI (around 48 BAR)
-
This high pressure is achieved by a belt-driven high-pressure fuel pump mounted on the engine.
Additional HPDI System Pressure Info:
-
Low-pressure fuel pump (from tank to VST): Around 4–6 PSI
-
VST (Vapor Separator Tank) internal pressure: Around 35–40 PSI (feeds the high-pressure pump)
-
High-pressure fuel pump output: Feeds injectors at ~700 PSI
-
Air pump (for injector atomization): Supplies pressurized air to aid fuel atomization—critical for HPDI function
Summary:
The injectors in a Yamaha HPDI engine operate at about 700 PSI, enabling fine atomization for direct injection into the combustion chamber. This is a key feature that distinguishes Yamaha’s HPDI technology from EFI (Electronic Fuel Injection) and traditional carbureted systems.
Testing them properly requires a GDI-specific test bench. See links below.