The sensor mounted on top the EGR insert that you are asking about is called the EGR backpressure transducer. It modulates EGR flow during high engine load by using exhaust pressure. I cannot see from the photos, but underneath there should be a line running down to the EGR insert body tapping into the exhaust gas flow. The vacuum comes into the backpressure transducer from the the EGR carb vacuum port through a PVS valve. The PVS cuts off vacuum completely until the car warms up. Then the vacuum can pass through the transducer to the EGR valve and open it under normal operating conditions, but closed at idle. When you put a heavy load on the engine, there is higher exhaust pressure and the EGR closes until you go back to normal. This was put on a few 1975s and all 1976 big block fords.

 

I have a 1975 F250 with a 460 with factory A/C. Would you by chance know the original part number for the EGR spacer that came with this truck? The one that was on there was burnt, so I got an aftermarket spacer, but it leaks vacuum on the bottom side of the spacer, so I thought I would just go back with what was factory. Unless you have a better, less-costly option.

 

The EGR/carb spacer plate is aluminum, heat causes them to melt internally, they also tend to carbon up.

1975 F100/350 460: There are TWO different EGR/carb spacer plates, one is CA only / Look on the Warranty Plate for the DSO code. If it's 71 or 72 .. your truck was sold new in CA

 

There's no DSO code imprinted underneath where it says, "DSO".