Originally Posted By: OceanDoctor
Why don't they pull EGR from after the cat, so that partially burned hydrocarbons ar somewhat oxidized and muhc less sooty by the time they hit the intake valves? Why not a very low surface tension coating (teflon?) on the valves and ports? Why not one big dumb "TBI" style injector upstream for occasional spritzing? Why not an EGR operated by cam phasing alone, eliminating the intake valves all together (ok, I think I know why, b/c the ex. gasses are too hot, but hey).
The Cat creates some backpressure, that helps EGR gasses enter the intake.
Toyota has an engine that uses direct injection and port injectors for the reason you mentioned.
And the reason that timing isn't used for EGR is because you can't route a cooler between the exhaust gas and the intake end.