Why was EFI late?

Random Ynot thought.

Most automobiles received electronic fuel injection in the 80s, after computers and software took over electronics. Sophisticated analog EFI would have been easy in the 1930s with a little imagination.

Bendix tried to introduce a transistor system in 1957, but transistors weren’t ready for the task yet. GM, Chrysler and AMC offered it then quickly dropped it except in the Corvette. VW made the first successful injection system in 1968. I owned a couple of squarebacks, worked on the system and understood it. The control box, about the size of a hardback book, contained a transistor analog computer tracking throttle position, temperature and vacuum. It was mechanically and electrically sturdy, got better gas mileage than carbureted Bugs (32 vs 26), and passed EPA emissions tests.

Injection itself was common on the earliest automobiles. Before GM invented electric starting, some cars directly injected air or acetylene under pressure to get the engine turning, and one astonishing car had true fuel injection which was simultaneously a supercharger and automatic transmission.

The simplest electrical fuel injection would be an extra set of contacts on the distributor to trigger the injectors. This would be worse than a carburetor because it wouldn’t respond to important variables.

VW’s circuit could have been made with tubes in the 1930s, and more easily after 1948. Car radios with big glass tubes were common in the 30s, with MUCH more complex circuits than EFI. The EFI function could have occupied one or two extra tubes inside the radio box, sharing the same high-voltage DC power supply. One fancy car radio came close, using an airflow sensor in the engine compartment to sense fan speed as a proxy for noise level, and turning up the radio volume accordingly.

Submini tubes were originally designed for aircraft usage. Compared to ordinary tubes they were small, sturdy, and needed much lower voltage, around 20 to 30 volts instead of 200 to 300. Transistors took the next step on all three of those qualities, but transistors weren’t fully ready for hard jobs until 1965.

From left: Rugged metal tube used in car radios, smaller tube typical in the 50s, submini tube, two transistors. A tube could generally perform two or three functions at once, so it took two or three transistors to replace it.

If the car’s main electrical system had been 24V instead of 6V, submini tubes would work directly without the vibrator, transformer and rectifier needed to power the plate circuits of big tubes. A 24V system has other advantages. Wires can be thinner and thus cheaper with higher voltage, and lamps can be brighter.