How does it work?

[WingingEd]

I replaced the spider injection on my '96 Silverado and now I have low fuel pressure (35lb). I suspected the pressure regulator so disassembled everything again and removed the regulator for inspection/replacement. Someone please explain to me how this thing works. I know there's no vacuum line connected to it and the entire area of the plenum acts as the vacuum, but I've checked three regulators with a vacuum pump and there seems to be no moving parts to it. I don't like to blindly trust that something just magically works without understanding how.

 

[L31MaxExpress]

I replaced the spider injection on my '96 Silverado and now I have low fuel pressure (35lb). I suspected the pressure regulator so disassembled everything again and removed the regulator for inspection/replacement. Someone please explain to me how this thing works. I know there's no vacuum line connected to it and the entire area of the plenum acts as the vacuum, but I've checked three regulators with a vacuum pump and there seems to be no moving parts to it. I don't like to blindly trust that something just magically works without understanding how.

Its like a positrac in a plymouth it just works.

All Joe Dirt jokes aside the regulator will not have a noticeable moving part applying vacuum to it. The spring does not move until the fuel pressure is high enough to start bypassing fuel back into the tank. The vacuum pulls on the diaghram with the fuel pressure and causes the fuel to be bypassed at a lower pressure when the intake is under vacuum. I can absolutely tell you that a correctly functioning system runs about 58 psi at idle and if you put a load on the engine, stall it against the converter it should rise to about 64-66 psi.

 

[c1500deathtrap]

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just a generic vacuum referenced fpr, Should help you get an idea for it. Theres quite a few different versions, in most cases vacuum pulls back a spring opening a bypass to return fuel to the tank or pump inlet. Reduced vacuum (more throttle opening or load) closes off the bypass port increasing flow to the injectors.

 

[WingingEd]

Thanks for the explanations, it helped me understand how the little thing works. I replaced the regulator and raised my fuel pressure to 51lb. holding steady. Still a little hard to start, but not like it was before. Ordered a new fuel pump which I hope corrects the hard-start. I originally started down this road because of a p0300 Random Misfire code. I have replaced all the ignition components and verified strong spark on each cylinder.