I got to my library today only to find that I have every new car intro manual for mercedes up to 93 except I don't have a 79. Not to worry I went to my service microfiche and pulled the one covering all the M117 engine emission systems from 72 to 80. The air pump always runs after it is picked up by a 17*C thermovalve.

EGR is activated through a 40*C thermovalve. EGR is activated during acceleration, during partial load, and during transition to decel. All this is done through a vacuum amplifier and is never shut off at higher temps.

I still think the idea of restricted coolant flow has some merit in high NOX readings. Remember theory is called theory, because it is just that. The reason that science progresses so slowly is because it always must follow scientific procedure. Tell that to Leonardo da Vinci

Peter.

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