it was Matthew's fault changing engine type through the postYou guys referring the RHZ EGR, a vacuum unit, will confuse the OP. Let's be clear you are referring to an earlier 2.0HDi dimi's C5 'Carlo5'. It's different to the electro-mechanical RHR EGR valve.
Excess smoke can also be casued by a split or blocked turbo air pipe. It can split. There is also an intake pipe that can collapse under suction from memory and starve the engine of air. It's worth ehecking the mechanical intgrity of those parts.
Shane , isn't your RCZ an RHH? If it is, the EGR is a very different and more complex beast, mounted on the front of the engine.
It's very different from earlier EGR systems, to suit Euro 5 engines, designed by Valeo. The exhaust manifold has an extra port to a passage that goes right through the head to the front. The unit is front mounted, with an electrically controlled and driven motorised valve. Operation is by signal from the ECU,
Attached is a water jacket with a butterfly valve to either divert gas flow through the jacket, or bypass it. Flow then proceeds to an outlet inside the flat plastic manifold fitting. The cooler bypass butterfly is driven by vacuum. The solenoid is at the rear of the head. The plastic manifold includes vacuum reservoirs at the back that feed the valves.
Removal of the jacket is barred - else it will leak.
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You certainly can't slip a plate behind the machined exhaust manifold.