Quote:
Originally Posted by Old Mechanic
the volume of gas in the combustion chamber
Wrong.
Test this with a vacuum gauge when you manually introduce EGR.
Vacuum drops, which means more mixture in cylinder at BDC on intake stroke, which means more compression at TDC on compression stroke. More in=less vacuum=more compressed=more compression.
Mech
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I disagree. The vacuum is dropping because you are displacing the oxygen available for combustion with the inert gas as was described. The requires the the throttle to open further to maintain torque. It is the increased throttle angle or increased IAC air volume that results in the drop in manifold vacuum.
This is want we want for fuel efficiency, that increase in throttle angle for the same load is what puts an engine with throttled intake closer to it's best bsfc.
What happens when EGR valve without a positino sensor gets stuck open? You get an engine that runs rich, or runs lean?