Fuel injection and fuel return valve question

Hey,

So, I've gotten pretty intimate with my fuel rail and injectors lately after my latest debacle. I have a question though about how the fuel amount works in the 3S-GE engine. Basically, I want to know how the injectors put more or less gas in, and what influences it. I'll say what I *think* happens based on what I've observed.

Here I go. I think that the fuel pump puts a constant pressure on the fuel rail. Injectors have to tick each firing, obviously. These motors don't seem to be dependent on just the RPM for increased fuel use though, as is basically any car, so it's not just base fuel use per firing * RPM (just as an example, I know that is totally bogus). I noticed the fuel return valve is connected to the TB via a vacuum line. I'm guessing that the fuel return hose puts fuel back before the fuel pump, or before the fuel filter, anyway. This makes me suspect that the fuel return hose is default open without vacuum, so less pressure (and hence less fuel) is on the fuel rail. But with vacuum, it gets closer to shutting off, increasing the pressure and fuel sprayed. Basically I'm saying, the more air flowing through the TB (more pushed in the pedal is and higher the RPM is, basically), the more fuel being pushed out through the injectors? It seems pretty intuitive and simple that way, please let me know if that's it or not. The other possibility I thought of was changing the duration that the injectors fire. Also, can the 3S-GE use the injectors differently as it chooses, or is it all dependent on the TB vacuum?

Let me know what you think and whatever I might be missing. This is all just a guess on my part; I'm really curious though.

Thanks!

--Teran

 

Thanks for replying. I guess it is; I always assumed those were one of the same. The intake manifold is directly attached to the throttle body, right? By memory, that pipe does seem to be going into one of the intake runners rather than the throttle body itself. Could you explain if my explanation of how much fuel is flowing is right or not though?

Thanks,
Teran

 

Sorry for the confusion. I'm not having any troubles on the car, just asking about what determines the amount of fuel the injectors push out under normal conditions, in a working Celica. From my understanding, it seems like the vacuum created by the intake manifold makes the FPR return most of the fuel back to the pump when the throttle is mostly closed, but when it is WOT and low or no vacuum, it is closed so there is as much pressure on the fuel rail as possible, which makes the injectors push out more fuel. Does that sound right?

Thanks,
Teran