The Lucas Td5 ECU is a very strange unit cos it's developped from a petrol ECU which initially was, it seems that those who made it didnt really care or understand how the diesel engine works from your(physical) point of view cos they included the MAF input in the air mass calculation table of the fuel map and the fuelling is managed mainly on MAP reading but it takes into account the air flow too so that's what the ECU does and it seems that the engine can live with it, for the Td5 to work perfect a well working MAF is needed regardless of EGR as the ECU uses the reading in conjunction with the MAP input to calculate air mass per cycle for the addaptive strategy... in this link
http://www.discotd5.com/ecu-tech/ecu-reverse-engineering in the first two images it's shown how the ECU uses the MAF input for that too, those images are confirming my own measurements as well, second paragraph from bottom here
http://www.web-rover.co.uk/nav.php?p=td5kb/intro too.
so THE REALITY is that the Lucas Td5 ECU doesnt care or understand how a diesel engine works but it gives the fuel to it based on MAF reading
too... that's another fact, and i'm sure there are other more modern ECUs which are doing the same cos the air mass in the cylinder will be more accurately calculated from two inputs which are not unlinked as the greater the MAP reading is the higher the MAF reading should be that's why the Lucas ECU can throw "air flow too high" fault code if there's a leak after the turbo cos it compares the MAP and MAF readings
for fuelling and at a certain air flow there must be a certain boost to match the fuel map and all the other elements are included in this calculation as ambient pressure, wastegate ratio, EGR ratio, rpm, driver demand, FT and ECT... also the Lucas ECU will log a "EGR stuck closed" code if the vacuum is removed from the valve without touching the modulator's electrics based on the same complex calculations....that's how the ECU works regardless of how mr Rudolf Diesel conceived the engine to run at it's beginning
