I just bought a 96 GMC Sonoma. It`s the 4.3L with the "w" in the vin. Vortec SFI. SLS, zq8 package, Power everything, 3.08 rear axle ratio, locking rear differntial, baicaly all options. I originally thought it was CPI, but on the window sticker it said VORTEC 4300 V6 SFI. Whats a SFI? Whats the difference between the CPI?