EGR Block on CRD Patrol

[the evil twin]

snip... but my thought is because now the intake is getting 100% cleaner and cooler air, not a mix of dirty hot exhaust gas aswell, the air can be compressed more, being cooler, hence slightly over boosting now due to a higher compression rate in the intake system.

Hmm... not sure about that.
Agree you can compress colder air for more oxygen but don't think that is what is producing the boost spikes in this case.
Mainly based on the fact that the EGR block doesn't change the air temp in the intake/turbo/intercooler

Only two things compress air, the Turbo and the Pistons.
The pistons are post-EGR block so the ECU/Scangauge/Boost gauge or whatever can't see that pressure.
That pretty much means the only way the ECU or gauges can 'see' an overboost is if the Turbo supplies too much pressure or if you get a back pressure.
I would be tempted to rule out back pressure as the EGR block is now a constant.

Sooo... I reckon the ECU is seeing the inputs (throttle, engine load, air flow, air temp, boost pressure) and commanding increased vane angle and closing the EGR valve it thinks is open and/or (depending on what is happening) has trouble backing off the vane angle to reduce the boost when it wants the EGR to open.

Bottom line is it doesn't matter too much either way as no EGR is awesome for the engine and shithouse for the planet :-)