exhaust "heat riser" vac pod, operation??

[libtec]

Hi and thanks for looking!

I'm trying to figure out when the vacume pod on the drivers side exhaust "heat riser" valve is supposed to operate and at what state does it sit when the pod actuator rod is fully extended? Without taking the pipe connection apart and looking inside I can't be sure where the valve sits when the truck is off and as far as I can tell the pod isn't moving the valve at any time. The rod is fully extended all the time. Is this pod controlled by the group of three solenoids mounted on the motor? I can operate the valve by hand, everything moves smoothly and the pod spring tension is good returning the valve to it's rest postition. Any input on operation and theory would be appreciated. Thanks again!


John.

[Lightyear]

I just learned that this gizmo on my '88 Burb is part of the EGR system. The Chevy manual says its normal state is 'open', not restricting the exhaust flow. The group of three solenoids on my engine seemed to energize at random, so I disconnected them. I'm also considering removing the EGR valve in the intake mainfold, depending upon what I read here in the forum. It seems to do no harm, but no good, either.
There was a 'heat riser' on my 1986 F150 gasser that failed, and it sounded terrible. I had the flapper valve cut out and the riser welded back in, and it ran GREAT.