I have had several of the CPI systems, and even though they have one common injector that pressures the poppet valves, vacuum from the intake cycle is required to open each poppet valve. Thus, it is a effectively a simply smart sequential system.
I learned this while trying to clean and test a CPI (spider) poppet valve. I had a mock up of a pressurized system using air pressure regulator and sea foam in the poppet tube. I could not get fuel through any nozzle until I applied air pressure through a venturi creating a vacuum to the exit of the poppet valve. Also sea foam had to be diluted with fuel to exit the nozzle.