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Plenty of people do it
Caveat #1, blanking the EGR is unquestionably illegal.
Caveat #2, most modern engines will throw a code if you simply blank it off. I am not really sure how they monitor it, I think what Ryan wrote is probably right in that the ECU will be looking for a dip in MAF reading as the valve opens. A lot of people pay for a tune and get the EGR disabled in software.
EGR should not impact DPF regeneration, it is actually used to reduce combustion temperatures, not increase them. The drop in combustion temperature reduces output of oxides of nitrogen, something that diesels are generally fairly nasty at. The high compression ratio lends itself to conditions that produce those emissions.
DPF regens are done by injecting additional fuel, either using the normal injectors after the normal combustion part of the cycle or some have an additional injector in the exhaust system which injects fuel directly to the exhaust. The goal being to ramp exhaust temperatures up high enough to burn the accumulated soot out of the DPF (Somewhere in the region of 700 degrees Celsius) I can certainly see the advantage to the supplementary injector, it means not subjecting the exhaust manifold and turbo and some sensors to the heat of a regen. Regens are pretty hot, if you have ever gotten out of a modern oiler and it smells like someone has been cutting steel with an angle grinder, that is probably a regen in action. I had one take the hair off my shin as I walked behind the car once.
Glen, I am not sure about EGR being a bypass path for boost on a diesel. Firstly, the only time I know of that the engines I am aware of close the throttle body is on shutdown (To make them stop more smoothly instead of the thud that the high compression ratio can cause) and actually during EGR operation to create a larger pressure difference and draw more exhaust in, given that diesels run without throttling. The other advantage is it can help stop a runway engine, google vids for runaway deisel if you want to see scary stuff. I am not at all sure they would provide much blowoff valve action as it is often the case that the exhaust manifold pressure on a turbo engine is almost the same as the inlet manifold pressure.
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