73-87 Chevy _ GMC Trucks > Fuel Systems and Drivability

Right EGR Supply Port at Rochester 1ME


I try to restore the emission lines at my 1978 250i6 engine and actual the egr isn‘t right installed.
At the Service Manual they write that „The diaphragm vacuum signal supply port is located in the
throttle body above the throttle valve“, but the only vacuum suply above throttle valve i know is where the choke vacuum diaphragm unit is connected.
Can someone make a photo where the egr is connected normally or knows a site where i can have a look?


For 1978 truck models with the 250 L6 engine and light-duty emissions, the EGR valve connects to "ported vacuum" through the EGR TVS (Thermal Vacuum Switch) - color added for clarity.  "Ported vacuum" means that the vacuum signal is zero at idle and increases proportionally with throttle opening while the engine is running.  The choke vacuum break (aka, pull-off) should be connected to a "manifold vacuum" port.

If your 1ME carburetor has only one vacuum port, it is not correct for an engine with EGR.

The vacuum ports should be physically arranged on the carburetor approximately as illustrated in the diagram, above.  The vacuum port for the choke break generally is not illustrated unless it is shared, via a vacuum tee, by a device external to the carburetor.

Thank you for the diagram an your answers. I will take a closer look at the carburetor again to see if I missed the connection somewhere, or if this is indeed not the right one for my engine.

Ignore this post  ;)


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