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spuggy spuggy is offline
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Join Date: Jul 2003
Location: Glorious Pac NW
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Yeh, Pat's got it. The WUR (or Control Pressure Regulator) controls the, well, uh, the control pressure. It provides warmup enrichment and boost enrichment, both of which drop the control pressure for more fuel (less resistance to the movement of the fuel head piston - and thus the flapper).

Changing the control pressure is just a big, coarse, richer/leaner adjustment over the entire range.

It's the fuel head that meters how much actually goes to the injectors, based on the position of the piston - directly connected to the CIS air flapper in the throttle body. Like an AFM that controls fuel flow directly and hydraulically without a Motronic, if you like.

The fuel head also regulates overall CIS system pressure via the regulator valve in the return circuit that goes back to the tank, but this function is unrelated to the fuel metering due to the flapper plate position.

With EFI, you don't necessarily need rising-rate FPR although it can provide extra tunability if you're a tad lean up top - the 951 guys tend to just swap out the stocker 2 bar FPR for a 3 bar item for mild to mid-range upgrades, which reduces the duty cycle on the factory injectors, or lets them avoid buying the next-step-up big-#-age injectors that make the idle really suck...
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'77 S with '78 930 power and a few other things.
Old 11-13-2007, 10:41 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #47 (permalink)