1973 EGR Valve Question

[Steve73QMach1]

I have the original EGR valves from both of my 1973 Mach 1's (built about a week apart). These have not bee installed for over 20 years. Here are the part numbers:

D3ZE-9D475-A1C (036) - with 4 speed transmission and dual point distributor

D3ZE-9D475-B1C (034) - with Automatic C6 and single point distributor

I was trying to clean them up a little which involved separating the valve body from the plate. After removing the gasket from both, I saw that the exhaust gas orifice in the valve body from the 4 speed car was much smaller than that of the C6 car. The 4 speed orifice has a 3 stamped in it and the C6 car has a 5 stamped in it:

Anyone know why this was done? Does the A1C vs. B1C in the part number denote this difference?

 

[secluff]

The D3ZE-A1C (D3ZZ-9D475-A) and D3ZE-B1C (D3ZZ-9D475-B) were engineering numbers used by engine plant during assembly and the parts dept to identify the Egr valve for the correct replacement. The number on the orifice washers was originally used by the manufacture to identify the correct washer use during valve assembly. As the number of EGR valve equipped vehicles grew, so did the staggering amount of different valves Ford had to stock in the Parts Depot's. Dealers neither had the room or the money to stock even a small portion of the valves in the part system. Ford eventually released some service valves that replaced about 75% of the hundreds of EGR valves in the system. They came with a package of orifice washers with numbers on them and a list of ID #'s to cross to your original valve. It would include instructions on which washer to use and if placed in downstream or upstream hole and staking instructions. There was also a label enclosed so you could transfer the original ID# to the new valve for future use.

There were three different basic numbers for the EGR valves (9D448, 9F452, 9D475).

The illustration shows the bottom where the orifice washer would be placed and the blank label on a 9D448 valve.

 

[Steve73QMach1]

The D3ZE-A1C (D3ZZ-9D475-A) and D3ZE-B1C (D3ZZ-9D475-B) were engineering numbers used by engine plant during assembly and the parts dept to identify the Egr valve for the correct replacement. The number on the orifice washers was originally used by the manufacture to identify the correct washer use during valve assembly. As the number of EGR valve equipped vehicles grew, so did the staggering amount of different valves Ford had to stock in the Parts Depot's. Dealers neither had the room or the money to stock even a small portion of the valves in the part system. Ford eventually released some service valves that replaced about 75% of the hundreds of EGR valves in the system. They came with a package of orifice washers with numbers on them and a list of ID #'s to cross to your original valve. It would include instructions on which washer to use and if placed in downstream or upstream hole and staking instructions. There was also a label enclosed so you could transfer the original ID# to the new valve for future use.

There were three different basic numbers for the EGR valves (9D448, 9F452, 9D475).

The illustration shows the bottom where the orifice washer would be placed and the blank label on a 9D448 valve.

Thanks for that information Steve. Do you know why a four speed car would have a smaller orifice than an automatic? From a performance standpoint it would seem like the less exhaust gas you re-introduced into the air/fuel mix the better but how did that get by emissions testing?

 

[secluff]

Steve, all that was calibrated by the engineers. That's why you'll see different calibration numbers on engine tags for A/T and M/T engines. From what I can remember on the non back pressure EGR valves, when your engine is idling, the EGR valve is closed and there is no EGR flow into the intake. The EGR valve remains closed until the engine is at operating temperature and is operating under load. As the engine load/RPM increases and combustion chamber temperatures rise, the EGR valve opens and starts to inject exhaust back into the intake. This was supposed to have a cooling effect that lowered combustion chamber temperatures and reduced NOX levels. The different operating conditions between the A/T and M/T cars probably had a lot to do with the different valves on your two cars. Each engine, transmission, differential gear ratio, with/without air, etc, combination had to be tested and certified. Remember...Big Brother was watching!!

 

[Steve73QMach1]

Steve, all that was calibrated by the engineers. That's why you'll see different calibration numbers on engine tags for A/T and M/T engines. From what I can remember on the non back pressure EGR valves, when your engine is idling, the EGR valve is closed and there is no EGR flow into the intake. The EGR valve remains closed until the engine is at operating temperature and is operating under load. As the engine load/RPM increases and combustion chamber temperatures rise, the EGR valve opens and starts to inject exhaust back into the intake. This was supposed to have a cooling effect that lowered combustion chamber temperatures and reduced NOX levels. The different operating conditions between the A/T and M/T cars probably had a lot to do with the different valves on your two cars. Each engine, transmission, differential gear ratio, with/without air, etc, combination had to be tested and certified. Remember...Big Brother was watching!!

Great info Steve - thanks for the reply. I had always assumed that these EGR valves were all the same for 1973 but now I see that they are specific to the car and its options. Good to know. Learned something new.