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The problem dates back a long time. When you close the throttle butterfly on an engine that is running at high RPM the manifold vacuum can approach the close to perfect vacuum of outer space. Under those conditions combustion is impossible and unburned hydrocarbons go ballistic.
Even my 37 Ford had a small spring loaded valve in the butterfly so when you got that super high vacuum, some air would flow through the engine. It also had the intake manifold heated by exhaust gas through a passageway that was right under the carburetor, which rotted out a lot of the aluminum manifolds long ago, on an engine that still had a hole in the grille and radiator for a manual crank option.
In the late 60s air injection became practically mandatory, where air was pumped into the exhaust to help with burning the fuel more completely. This was the era of air injection lines into the exhaust manifold.
Later when catalytic converters became mandatory, manufacturers eventually went with fuel injection which allowed for more precise control of fuel delivery. When they realised that they could just shut the injectors off when the vehicle was decelerating while still in gear, then they could eliminate the additional complexity of air injection systems.
In the transitional period from carburetors to FI the manufacturers tried a lot of different "solutions" with carburetors. I think Toyota was one of the last to finally go over completely to FI.
By the time 3 way catalysts were universal, FI was essential to preserve the cats.
It's interesting to see what developments are coming with the availabliity of massive memory and super fast computer calculations. Multiple injections directly into the cylinder while combustion is underway allow ultra high compression with regular fuel. Spark knock is impossible. A long road from the DB 601 engine in the German Me 109 of the mid 1930s with direct injection. You have to see the humor in the "new" direct injection that dates back almost 80 years in aircraft, possibly even longer in other applications.
DFCO was one of the first "advancements" that became possible with computer controls. Nissan went with an EFI system, licensed from Bosch in 1975. It was simultaneous injection, not sequential. They did not need any catalytic converter, EGR, or air injection in the 1975 Federal versions of the first 280 Z. I believe this had DFCO but I can't be absolutely sure. My 76 280 had a N47 early EFI head, on a factory new 83 short block with flat top pistons. This raised the compression from 8.5 to 1 to almost 10 to 1. 160 PSI to 190 PSI on a compression gauge.
It required the base timing to be dropped from 10 to 7 degrees and premium fuel only. With the .75 overdrive 5th gear and the stock 3.54 rear axle 3k RPM was good for right at 85 MPH and at 65, she would push close to 30 MPG highway, with a Motorsports aero kit and lexan headlight covers.
regards
Mech
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