How to Repair and Maintain Bosch D-Jetronic Fuel Injection

How to Repair and Maintain Bosch D-Jetronic Fuel Injection

Electronic fuel injection EFI used from 1970 to 1975

When dealing with D-Jetronic, you need a good understanding of how it works. Without that knowledge, you will have a very hard time troubleshooting problems that show up - and there will be problems.

D-Jetronic is an early electronic fuel injection system that was very advanced for its time. At its core, it works by electronically measuring the engine’s operating conditions and then controlling the amount of fuel injected via electric pulse fuel injectors.

First, it uses sensors. The main one is the manifold pressure sensor, which reads how much vacuum is in the intake manifold. This tells the system how much air is being drawn in. There’s also a throttle position sensor to detect how open the throttle is, and temperature sensors to know how hot the engine and air are.

Second, the control unit, which is an early computer, takes those sensor readings and calculates how long to open the injectors. The injectors, in turn, spray fuel directly into the intake ports, just upstream of the valves.

Third, the system injects fuel in timed pulses. While it’s not as precise as later systems, it uses the engine’s RPM and the input from the sensors to get close. The injectors all fire at once per engine revolution, so it’s batch-fired, not sequential.

Finally, by adjusting fuel delivery based on load, throttle position, and temperature, D-Jetronic keeps the air-fuel mixture balanced—enough fuel for power, but not too much. It was a leap into the modern era, paving the way for today’s fuel injection. With everything working together, you get reliable combustion, and that keeps your engine running smoothly.