I have a 98 6.5 liter in a 1/2 ton "S" engine,the engine runs without the EGR but as soon as I bolt the EGR on the upper manifold the engine dies,is my cat plugged?Is the EGR passage through the engine plugged?
Currently walking,any help would be greatly appreciated.

Thanks

Hockeyguy

 

you can run your engine without the egr so its no big deal in my eyes

 

I suspect the upper intake is plugged or the "mystery gasket" between upper & lower plenum is rotten and you are full flowing EGR, with the EGR valve off you are open to air running basically as a N/A.

OBD-II S engines can not run without EGR unless you do some tricks, but 1st thing to check is the upper plenum, remove the 6 bolts in upper plenun take it off the lower intake and see if that upper plenum isn't all carboned up inside. this can happen when the small donut gasket that fits in the center "tower" for EGR leaks and you get full flow heavy sooty stuff that clogs the upper intake tract. Same thing can happen on OBD-I S trucks. Permanent fix is F upper & lower intake, some guys put freeze plug in center of the tower under the EGR valce to plug flow, that works on OBD-I a little different method needed for OBD-II.

F intake design also has more open plenum no slots in that upper it is wide open,

Called a "mystery gasket" because a lot of guys don't know it is in there

Part # used on 94-99 S engine OEM – 10191428, AC Delco - 219-167, NAPA - 2-25203