vac line question.
 

on an s4 na, does the FPR need to see a vacuum source or just filtered air?? also ive seen in some diagrams for rats nest removal, that shows the nipple on the lower intake by the oil injectors connect to one of the nipples by the plenum. what is this for and is this needed?

thanks.

FPR needs to see the pressure/vacuum from the dynamic chamber. That's the source of vacuum on a 86-87 non turbo.

It absolutely much be connected to a source of post-throttle manifold pressure. Read post #12 in this thread for an explanation why.

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/factory-fuel-pressure-627138/

It's an air bleed for the primary injectors, which improves fuel atomisation. The better fuel is atomised, the more completely and effectively it burns. So while the engine will run without it, there's not good reason not to connect it up.

The NZ explained it better.....but attached is a jpg out of the FSM showing the hose for the FPR and how it comes out of the dynamic chamber.

perfect. thank you both.

i couldnt tell where it was coming out in the diagram before. all the lines are so jumbled in the rats nest on those diagrams.

It goes from that nipple on the dynamic chamber TO the FPR solenoid (orange plug on the solenoid), and from there to the FPR itself.