I was following this thread with some curiosity...
6.4 EGR Questions
Richard Dawn mentioned unplugging the EGR on his Ford truck which resulted in better gas mileage. I was skeptical that this was actually done on a 6.4 so I tried it myself out of curiosity.
Unplugging the EGR seemed to create less power for my truck. The motor ran erratically and never achieved peak boost (about 36 psi on the gauge is my max). It also resulted in the CEL illuminating. I was afraid to run the truck for a significant distance due to those reasons. Needless to say, I didn't drive it long enough to determine whether or not I got better gas mileage. So I plugged it back in. I assumed that the EGR was stuck in an open position (see why later). FYI, I unplugged the EGR with the motor off, before restarting it and running it.
I remember reading somewhere that the 6.4 regulates max. boost through the EGR. The valve opens progressively the closer you get to max boost feeding itself more exhaust gas. I also remember reading that the EGR closes during a regen and that the valve consists of a "stepper motor". I assumed that the stepper motor meant that the valve would open and close through electrical current by the PCM. I do not know whether or not it has a return spring to return it to an open or closed position.
Since I already had a CEL illuminated after driving considerable miles with the EGR plugged back in, I decided to experiment. Why not? The next time the motor went into regen, meaning a closed EGR valve (right??). I unplugged it again. I was going to see if the EGR stayed closed resulting in a higher peak boost. THE MOTOR IMMEDIATELY CAME OUT OF REGEN! I have driven a couple of hundred mile since then with no regen.
I never did drive the truck after unplugging the EGR during regen to see if it actually created more boost. In hindsight I guess I was surprised due to the abortion of the regen process.
This begs the question of whether or not it would terminate regen resulting from the permanent regen condition due to a removed DPF.
Do not perform this operation if you do not want to see a CEL. Mine is permanently on and I suspect I will have to go the dealer and play dumb to have the code removed.
I know this little experiment is somewhat pointless considering the aftermarket tuners are very close to disabling the regen process for good (excluding KEM). I felt it was my duty to post my observation and see what you all thought.