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Working more on the ECU, still not finding much info at all on this ECU, but I believe I found the VVT table and it seems like there is WAY too much valve overlap at low load, which may be why the gas mileage is so atrocious at low speed.
For some reason, all these years I've been a car enthusiast I never bought a legit OBD2 scanner that is fast enough to actually datalog, so I just ordered one off Amazon (Veepeak, still a relatively cheap one at 32 bucks, I watched some Youtube videos and it seems to log more datapoints than I can count in 1 second, which is good enough). I'll look at the logs and try to estimate how much internal EGR is going on so I can reduce the cam overlap if needed.
Unfortunately, the Jaguar VVT actuator seems to have a very limited range of 37 degrees (could be more, but eyeballing a picture of the physical mechanism agrees), and messing with the VVT position too much could throw off the spark timing since I don't know if there is VVT based spark timing compensation. Of course, if the spark timing logs show pretty sensible numbers, then I would be in the clear, so hopefully that's what ends up happening.
However, if the logs do suggest extremely poor combustion efficiency from big cams and lots of valve overlap, then I won't be trying to utilize much more external EGR and thus don't need to worry about spark compensation for EGR.
Figuring out DFCO is probably the next priority, but the lack of DFCO can be mitigated by braking in neutral with a lower idle speed (not great, but better than guzzling fuel in gear with foot completely off the pedal :/).
I'm still optimistic I can get a 26mpg cruise, high 20s pulse and glide, and something like 16+mpg "city".
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