How does the TBI (I'm assuming 747, I haven't looked. It's my '92 K1500, L05) deal with EGR? More specifically, what does the ECM do when the EGR opens and how does it know to set a code?

Specifics: It's been running funny for a little while, after it gets warm under light throttle/part throttle cruise it was surging. I couldn't find anything _really_ wrong with it, so I started experimenting. On a whim (mostly based on when it was happening) I plugged the line between the EGR solenoid and the EGR valve. Surging is gone, gas mileage is up and we're back to the nice, happy truck, with the exception that the service engine soon light comes on occasionally (EGR code). So besides just disabling it, I'm wondering what's supposed to happen with the tune when the EGR opens and how the ECM figures out that the EGR is open.

 

when it triggers the valve to move the EGR, it expects to see a pressure change in the manifold.

if you do a search on EGR with my name, you'll find some more info on it.. i had a similar question about 8-12 months ago.

 

Yup, and old school fix for removing EGR and not getting an error code was to install a check valve from some crappy Honda .
EGR is a weird beast that I have never taken the time to play with (my car doesn't have it).

 

Huh, sounds like what my '97 does… that one I got tired of because the EGR tube kept melting the rear seal on the intake causing an oil leak… since the heads have no egr passage that one was an easy fix, welded up a block off for the exhaust manifold end, and then made a fitting with a small filter on the egr inlet end so when the EGR opened it lets fresh air into the manifold.

Huh, check valve from a Honda??? Where does the check valve go? I'm wondering what would happen if I just disconnected it and maybe put a small filter on it… EGR solenoid opens, creates a vacuum leak and the MAP sees a pressure change. Hell, if it turns out that the pressure change isn't enough I could actually plumb the source for the EGR solenoid into the MAP line and then adjust how much a pressure change it sees with a needle valve.

'Dude... funny, searching for your name and egr got me 29 threads...

 

<-- searched 'JPrevost and EGR' found 171 .
Definatly do a search on disabling EGR. The checkvalve will make your ecm think there is EGR active and will advance timing in stock calibrations. This is not what you want because if you don't have EGR it means that anytime the ecm isn't commanding EGR that you're running not enough timing under cruising... or you knock every time EGR is enabled.
Keeping EGR or disabling it comes down to preference and will power to keep the green tree huggers happy or your engine happy.