okay I dont exactly know how the fuel system works, but I want to. here is what I have as what I think I "know". the fuel is delivered to the fuel filter from the tank courtesy of a fuel pump, fuel pump goes to fuel rail. at the fuel rail there is an AH HA! fuel pressure regulator this regulates fuel PSI in the rail correct? the injectors are connected to the rail, are they computer controlled? and if you got an adjustable FPR and raised the pressure wouldnt you just end up running rich all of the time you were not....say for example using nitrous oxide... or do the injectors have some other control besides just the pressure in the rail, and is the stock FPR not regulated by a line that connects to the IM making it a variable pressure right? so if you get an adjustable FPR how would it keep frpm delivering too much fuel when it is not needed? IF anyone cares to try to explain the whole thing you get a free thanks

 

Yes, a Fuel Pressure Riser will make you run rich. Unless you have bolt-ons that lean you out. The factory ECU is tuned according to the stock intake, exhaust, etc. When you add bolt-ons that increase air flow, you may be running lean on the fuel side. Under normal acceleration and driving the ECU gets input from your O2 sensor and adjusts the Air/Fuel Ratio accordingly. Under Wide Open Throttle the ECU sends a pre-programmed fuel curve to the engine which is not modifiable from O2 sensor input. This may be fine on the stock engine and usually is a little on the rich side anway. On a modified engine it just may not be enough to keep a stoich A/F ratio...it may go a little to the lean side (bad).

You probably don't need to mess with the stock fuel pressure. I bumped mine up a couple PSI and my car just ran really rich all the time. I have intake, header, exhaust (very free flowing with no cat). You would be much better off getting a VAFC and getting it tuned. This will be much more accurate and you won't be running really rich all the time. The VAFC delivers more fuel by lengthening the injection pulse rather than squeezing more fuel in per pulse as with a higher fuel pressure.

When using nitrous oxide (or any forced induction) you should always have a way to increase fuel delivery. In a Wet kit, more fuel is added by an additional nozzle or injector adding a proportional amount of fuel according to the amount of nitrous delivered. In a dry kit there MUST be some way to increase fuel delivery. In the ZEX kit, when the nitous is activated, the fuel pressure is raised according to nitrous tank pressure to ensure a somewhat accurate fuel delivery. Both the nitrous and fuel pressure increase are activated at WOT. This is why many say ZEX is foolproof. I do not have experience with other nitrous systems so I can't say what they do. I would imagine they all support some means of fuel enrichment.
Hope this helps...

 

Stew is right on the money


One thing I would add is that the fuel pressure regulator comes between the fuel source and the fuel rail.

injectors are computer controlled. they are rated at specific flow rate. the computer figures out how long to open them for. how much fuel gets sprayed is dependant on the flow rate of the injectors and the fuel pressure in the rail


[Modified by jweller, 8:32 AM 3/7/2003]

 

Sure looks to me like the FPR is on the return line... That thing on the supply line is to dampen out pulsations.

 

Correct. The FPR lets pressure build in the rail. When the pressure gets to high the FPR "vents" the excess.