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patkeefe patkeefe is offline
one of the great unwashed
 
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Join Date: Apr 2004
Location: Ringwood, NJ
Posts: 2,843
Since I forced myself to learn jack about CIS (although I am ignorant to the inner workings of the true 930 system), they are a more stone age fuel delivery system than the EFI stuff. Fuel delivery is controlled via the WUR, or control pressure regulator, which can be thought of as a bleed. As the engine wants to get richer, ie cold, the control pressure drops, or bleeds, and basically gives the engine more fuel via the fuel head and injectors. Once warm, the n/a WUR just pretty much maintains a set control pressure. Fuel delivery volume changes solely due to the rise in the plunger from the airflow plate, which thus meters the correct dosage of fuel. The 930 WUR has a boost enrichment which allows boost to work the WUR diaphragm, and drop the control pressure, feeding the engine more fuel.

I couldn't get AFR's rich enough with a stock WUR from the SC, so I ended up getting a 930 WUR, along with an IA fuel head modification. I also have an RPM boost switch, which delays the onset of boost enrichment to a predetermined RPM, to keep from getting pig rich in the mid-range. These few CIS mods were $1000 worth, plus a load of tweaking. If you start with EFI, in my mind, it just has to be simpler.

BTW, mmn710, have we scared you off yet?
Pat
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Patrick E. Keefe
78 SC
01 Boxster
Old 11-12-2007, 04:19 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #46 (permalink)