How much vacuum is required to open the oil metering pump nozzles on a Mazda RX-7 FD?

Zero vacuum is required to open the oil metering pump (OMP) nozzles on the Mazda RX-7 FD ¹.

Engine vacuum and boost are not used to trigger or activate oil injection. Instead, the OMP itself is a positive displacement pump that meters the oil volume. The nozzles act as banjo fittings with internal check valves that possess a very low crack pressure, generally less than 1 PSI ¹.

The air port on top of the nozzle is highly misunderstood and actually serves two purposes:

1. Siphon Prevention: It prevents the engine's intake stroke from sucking all the oil out of the lines. By pulling in a small amount of air instead, it functions much like a hole in the side of a drinking straw.
2. Atomization: It draws in fresh air to help atomize the oil as it enters the combustion chamber ¹.

Routing Options (Difficulty: Easy)

Because these ports only need a clean air source rather than a vacuum signal, you have a few acceptable routing options depending on your setup:

• Stock Routing: The lines connect to the plastic elbow on the front of the primary turbo, which provides filtered, non-pressurized air.
• Single Turbo Routing: Tap the intake pipe anywhere between the air filter and the turbo compressor housing.
• Vented to Atmosphere: Leave the lines open to the atmosphere, preferably capped with small breather filters to ensure the air being drawn in is clean ¹.

Safety Warning: Never route the OMP air lines to a pressurized boost source on the upper or lower intake manifold. Exposing the nozzles to boost opposes the check valve and can cause a bad MAP sensor reading, severe detonation, or total engine failure if a line blows off or a check valve fails ¹.