EGR Do I need it offroad

[IsaacHayes]

You can get rid of an external EGR valve by doing internal EGR. You do this by having valve overlap of the intake/exhaust. So you have exhaust gasses remaining which causes displacement of oxygen (the main factor in how the EGR works to reduce NOx emissions). The 2001+ LS1 got rid of the EGR valve and changed the cam profile to do this.

Now at load and low speed the exhaust gasses can be too high sometimes with valve overlap, so this is where VVT comes in and can adjust the overlap. (and also make the engine smoother, where as I'm guessing the LS1 with overlap people didn't mind a rougher idle since it was a sports car)

[motorbreath]

VVT is a kind of EGR if you want to think of it that way. Instead of recirculating the egr through the intake it holds a small amount of exhaust gas in the chamber which pretty much accomplishes the same thing as the EGR valve. Not only does it keep you combustion temps down but it keeps your intake clean too unlike regular EGR valve systems. Buildup in the intake from recirculating exhaust gasses is was casues codes like EGR flow insufficient, ect. because the port in the intake gets plugged.

Happened all the time to the Impalas with the 3400's when I was at the taxi company. just poke a coat hanger through the tb to open up the port and spray it out with carb cleaner with the egr valve off.

As for the old style vacume EGR valves they should work off of (iirc) ported vacume, before the TB. Because when you open the TB manifold vacume drops but ported vacum rises. If they worked off of manifold vacume I would think they would be wide open at idle which would make the car run like crap. But correct me if I'm wrong.

[torq455]

if you look into the TB, there are a couple of small holes in front of the throttle plate. so when closed, no vac to the egr. in order to get vac for the EGR, the plate would have to be just past one of the holes--light acceleration. then when the plate goes further past the holes, the manifold vac begins to go down slowly. thus, the EGR begins to close. i believe this is the same for the CCP.

[motorbreath]

I'm not all that familiar with the old type but that sounds about right.

[torq455]

really not much different with the newer EGR cars, but now it's more for the FPR and CCP since the EGR's are digitally controlled.

[motorbreath]

You know I jsut remembered that the older EGR valves also had a selenoid that controlled the vacume as well. So the computer (cars that had them at least) did have some sort of control over them.

[geoffinbc]

Yea that is like my truck. The EGR switch has constant vacuum but the position of the valve is controlled by the ECM when it commands teh switch.