Jim Klein recently posted a junkyard post on a 1977 Cadillac Seville. Not only was this an awesome junkyard find, but it stirred up lots of conversation in the comments section. Of particular interest was the fuel injection system. When the Cadillac Seville was introduced in late 1975, it included an electronic fuel injection (EFI) system on its Oldsmobile 350 engine. This made it the first American car to come equipped with electronic fuel injection as standard equipment, a fact commonly forgotten due to its reliability issues.
Cadillac did not limit its electronic fuel injection to the Cadillac Seville with its Oldsmobile 350 engine; it was also available as optional equipment in other Cadillacs equipped with the 500 cubic inch Cadillac V8 engine and later the 425 V8 engines through the 1979 model year (there was some availability in 1980 on 350 Oldsmobile powered Cadillacs). This fuel injection system delivered a much more precise fuel and air mixture, allowing the engines to burn cleaner, use less fuel and have considerably improved drivability. A positive side effect of the cleaner and more efficient fuel metering was that the Oldsmobile and Cadillac V8 engines were able to be tuned to produce more power while meeting emission standards than their dirtier carbureted versions.
Despite this system being the first mass produced EFI system offered by a domestic manufacturer, there is little information about this fuel injection available today. Likely part of the reason is that it was dead end technology, being an open loop analog fuel injection system. Cadillac completely abandoned this system in 1980 with the introduction of its digital electronic throttle body fuel injection. Nothing was carried over from the analog EFI.
The analog EFI used by Cadillac was a joint effort between Bendix and General Motors. Bendix’s history with electronic fuel injection dated well before 1975. It introduced an EFI system in 1957, called the Bendix Electrojector system. In 1957, this system was optional on the Rambler Rebel, with estimates of 0 to 6 cars equipped with the option. In 1958 it was offered on some Chrysler products, with 35 Chrysler, DeSoto, Dodge and Plymouths so equipped.
This original EFI was very complex and the electronics of the time, in particular the semiconductors, were not advanced enough to create a durable electronic control unit. Although I couldn’t find any primary sourced material, sources claim that Bendix sold the intellectual property for its electronic fuel injection to Bosch. With this, Bosch developed the much more successful Bosch D-Jetronic, introduced in 1967.
The fuel injection system that Bendix developed with Cadillac in the 1970s shared many similarities with the Bosch system. I couldn’t find any definitive sources that explained the finer details of Bendix reusing the same technology that it had sold to Bosch. That said, while the Bendix Cadillac EFI had many similarities to the Bosch EFI, the Bendix-Cadillac EFI was was an independent design that used almost all Bendix or General Motors parts.
The Bendix Cadillac EFI is a multi-port electronic fuel injection system. Unlike later fuel injection systems, it was an open loop system. This meant there was no oxygen sensor which could read the exhaust and monitor the fuel air mixture to adjust accordingly. This open loop system simply had to rely on preprogramed fuel mixture charts which were used based on the inputs from the engine sensors. The Bendix Cadillac EFI consisted of three major systems; the electronics system, the fuel delivery system and the air induction system.
The electronic system was controlled by a computer called the Electronic Control Unit (ECU). There were a series of inputs fed into ECU. These inputs were interpreted by the ECU and were used to calculate the appropriate amount of fuel to be metered into the engine. As seen in the diagram above the input data came from a number of electronic sensors. These included a coolant temperature sensor, a manifold absolute pressure sensor, an intake manifold air temperature sensor, the engine RPM and the throttle position sensor.
The ECU could interpret the data (voltage) from each of these sensors to understand the engine’s operating conditions and the driver’s desired response. For example, if on a hot day the driver was going up a steep hill at high speed and had downshifted to second gear, the ECU maight see a high coolant and air intake temperature, low manifold pressure, high engine RPM, and the throttle will be opened significantly. From this data, the ECU would calculate that the engine would require a large quantity of fuel to be delivered.
The ECU controlled a series of output devices to properly deliver the correct fuel mixture. It controlled the eight fuel injectors to spray a predetermined amount of fuel through a precisely time burst. The quantity of fuel was controlled by the length of the burst. The fuel injectors were batch fired, meaning that numerous injectors fire simultaneously, unlike the later sequential systems which fired each injector in sequence (similar to spark plugs). For the Bendix Cadillac EFI, the system was divided into two injector groups: Group 1 was cylinders 1,2,7,8, and Group 2 was cylinders 3,4,5,6.
The ECU controlled other components in the fuel injection system besides the injectors. This included the fast idle valve, which was used when the engine was cold. It also controlled the EGR solenoid, limiting the conditions that the EGR valve was opened. Other cars of this era typically used thermal-vacuum switches to control when the EGR valve operated. And finally, the ECU controlled the dual electric fuel pumps. The ECU would activate the fuel pumps when the ignition was turned on and the engine was cranking or running. It also deactivated the pumps when the engine stopped running, or if the driver turned the ignition on but did not start it within a short period of time.
The fuel delivery system was significantly more complex than the typical mechanical fuel pump with a single feed fuel line of the era. The Bendix Cadillac EFI had two separate electric fuel pumps. One was a pump mounted in the fuel tank. This was a small boost pump that simply feed a larger externally mounted pump. The small pump helped prevent vapor lock by keeping the large pump from having to suck the fuel from the tank. The large pump was a constant displacement, roller-vane pump mounted to the chassis. This pump feed the engine and was responsible for producing the high pressure required for the EFI. It also incorporated a check valve to maintain fuel pressure when shut off. From there the fuel flowed through a fuel filter, and then to a fuel pressure regulator that maintained the 39 PSI required. The fuel pressure regulator feed the fuel rails and injectors, while excess fuel was bled off and returned to the tank via the return line.
The air induction system was similar to that used by the carburetor equipped variants, but there were a number of significant differences. Air was fed into the engine with a dual bore throttle body. Like a carburetor, the throttle body controlled the air into the engine via butterfly valves actuated by the accelerator pedal. The throttle body also had a fast idle air valve. This valve would open when the engine was cold to allow more air into the engine and increase the engine speed. The valve had a thermal element within that warmed up and slowly closed the valve as it did so. When the thermal element reached approximately 140 degrees, it was fully closed and ineffective. At this point the engine would be warm enough to not require a fast idle.
The throttle body is mounted to an intake manifold and it is similar to the intake manifolds used by the carburetor equipped engines. The biggest and most obvious difference was the addition of fuel rails with injectors mounted near at the end of each port at the cylinder head. The EFI intake manifold did not use an exhaust crossover. This is a passageway under the carburetor where warm exhaust would heat the incoming fuel air mixture from the carburetor to help improve atomization in colder conditions. The EFI manifold was dry, meaning only air passed through, making the exhaust crossover not required.
Many of the sensors and electronic components used on this EFI system became common place in the 1980s, but during this time in the 1970s they were uncharted territory for the American manufacturers. Like other technologies in their infancy, this made for some growing pains. Cadillac had to manufacturer many variations of the ECU, each calibrated for different models and/or drivetrain configurations. This resulted in a much more costly and complex ECU part supply. It wasn’t until the 1980s that GM began to use ECUs with removable PROM chips, which would allow for one basic ECM to have many different variations by using different PROM chips.
GM and Bendix supplied most of the EFI components other than the throttle position sensor which was a Bosch unit, meaning most of the components were new and unproven. Unusually, the MAP sensor was mounted in the ECU itself, which was mounted in the dash of the car. The MAP sensor was prone to failure as were many of the other components used in this EFI system. There were many reports of component failures that lead to no-starts, and other driveability issues. This combined with many technicians being completely unfamiliar with EFI meant not only did the systems fail, but more often than not they were not able to be repaired correctly. And to top it off, parts for these systems were extremely expensive and often difficult to obtain. Surely this must have soured more than a few Cadillac customers.
Cadillacs of the 1970s are heavily criticized for being substandard cars compared to past models, and much of it is justified. Despite all of the short comings of the era, Cadillac’s EFI was somewhat of a valiant effort to introduce the latest technology. The Cadillacs equipped with EFI were much better running cars and had improved power, fuel economy, throttle response and emissions. Unfortunately, like much of what GM and other domestic manufacturers did at the time, the effort was good up to a point.
The EFI was failure prone while being costly and difficult to repair. The technology limitations were partially to blame, but GM certainly didn’t put enough development effort into this technology before it was released to the public. Ironically, after numerous other technology failures such as the variable displacement engine, HT4100 engine, Cadillac actually reverted back to a carburetor in 1986 when most other American cars had switched over to EFI. The big Fleetwood Brougham was powered by the 307 4-bbl Oldsmobile V8 engine until 1990. In 1975, it seemed like a good idea to install EFI into Cadillac’s flagship car, but its poor execution was one of the first of many hits to its reputation. Perhaps that might even qualify it to be a GM deadly sin, but I will leave that up to you to decide.