Originally posted by Russell-3L:
EGR and what it really does:

egr recycles waste exhaust gas puts it back into the cylinders (as much as 10% of the total air intake of the engine on some engines) its NOT used to "reburn" unburned gasses. its used to take up space in the cylinders thus using less fuel. it also cools down the cyl temps to reduce NOx emissions. EGR does not function at WOT. it doesnt help performance at all. it DOES increase gas milage and reduce emissions. thats all its designed to do. but what do i know....im in class now and taking the test for my PA emissions license feb 1st.....



Although mostly correct, there is one error in what they are teaching you. EGR does NOT improve fuel economy. I used to teach this stuff for for people getting their smog license.

EGR lowers peak combustion temperature. Basically because it has already been through the combustion chamber, it is just inert filler. It is about like injecting an inert gas instead, such as pure nitrogen, argon, or any of the gasses used to keep the metal from reacting with oxygen in mig welding.

EGR does not "lean out the mixture". Instead, it just adds fluff, something that can't burn.

Once EGR is introduced into the equation, fuel curve and ignition timing can be somewhat optimized for the less than ideal situation. If done properly, little if any drivability issues are generated. If not done properly, power will be worse than it could be, there can be engine hesitations, engine surges as the EGR is introduced, and there can be "chuggle" or "trailer hitching".

If the timing and fuel curves have been designed (or set by the factory) for EGR, then again, they must be altered to keep from having engine ping or fuel mixture problems.

Jim Johnson 98 SVT 03 Escape Limited