Perfect Burn - Learn the ins and outs of vintage and modern Fuel Injection

In the 1960s, carburetors ruled automotive fuel delivery, lingering in some economy cars into the early '90s. But Porsche, ever the innovator, took a different path. By the late '60s, they were pioneering Mechanical Fuel Injection (MFI) for their high-revving Flat-6 engines and even the Type 908 Flat-8.

Proven on the racetrack, MFI found its way into street cars like the 1969 911S. This intricate system, with its pump-driven hard lines and spring-pressurized injectors, remains a favorite among collectors and vintage racers for its precision and versatility. However, its complexity and cost made it impractical for mass production.

Enter the 1970 Porsche 914, a budget-friendly model that demanded a new approach. Porsche turned to Bosch for the D-Jetronic Electronic Fuel Injection system. The “D” came from the word "Druck" (German for pressure), D-Jetronic used analog inputs from an intake manifold pressure sensor and distributor triggers to control injector pulses based on engine speed. Despite its simplicity, D-Jetronic offered benefits like easier cold starts and altitude adjustments, thanks to temperature and pressure sensors. It suited the 914 well, but the 911’s more demanding engine required something more sophisticated.

This led to the Bosch K-Jetronic, or Continuous Injection System (CIS), introduced for the 911. As with the “D” from the D-Jetronic system, the “K” came from the German word "Kontinuierlich" (continuous), CIS constantly delivered fuel through injectors, with airflow dictating fuel pressure via a vane-operated fuel distributor.

While effective for its time and widely used in German cars of the '70s and early '80s, CIS struggled with performance modifications due to its rigid analog design and reliance on mild cam profiles, limiting power potential.

As the 914’s Type IV engine grew to 1.8 liters, it adopted the Bosch L-Jetronic system. Named for "Luft" (air), L-Jetronic improved on D-Jetronic by borrowing CIS’s air intake vane to adjust injector pulse width via variable resistance. It also included temperature sensors for better air density prediction and cold-start performance. However, like CIS, L-Jetronic’s simple mechanics struggled with wear and performance upgrades.

By 1983, the Porsche 944 introduced Bosch Motronic, a leap into computer-controlled fuel injection. Adopted by the 928 and 1984 911 Carrera, Motronic used a Mass Airflow Sensor, flywheel sensors, and later hall-effect sensors to precisely manage injector pulses and ignition timing. By 1987, the 944S’s 16-valve engine featured sequential injection and cam position sensors, boosting efficiency and power. Yet, Motronic’s mass airflow sensor remained a wear-prone bottleneck, and its tunability was limited to mild cams and chipset swaps.

These early systems—D-Jetronic, K-Jetronic, L-Jetronic, and Motronic—shared two flaws: limited tunability due to analog calculations and wear from aging components like wipers and sensors. For classic Porsche owners, this can stifle performance upgrades and reliability.

Fortunately, modern Electronic Fuel Injection (EFI) systems are hitting a price point that offers a real and viable solution to the home mechanic and beyond. Today’s EFI uses advanced sensors for air density, manifold pressure, exhaust gases, and precise RPM tracking via hall sensors and trigger wheels. These feed real-time data to an Engine Control Unit (ECU), which optimizes ignition timing and injector pulses for ideal air-fuel ratios. Gone are the days when you have to tailor your cam(s) and pistons to your fuel injection. EFI simply doesn’t care! Build that Monster motor of your dreams. Many systems ditch distributors for reliable coil packs or coil-on-plug setups, enhancing spark accuracy and eliminating wear points. Some ECUs even auto-tune in real time, simplifying setup and boosting performance.

Ready to upgrade your classic Porsche? Start with a modern ECU like the Megasquirt MS3, an affordable, user-friendly option with free software and auto-tuning capabilities. For throttle bodies, Jenvey offers high-quality standard or heritage-style units for 914s, and three-barrel options for Flat-6 engines. PMO also provides top-tier throttle bodies for Flat-6s. You’ll also need spark plug wires, ignition coils, a crank trigger wheel, hall sensors, O₂ sensors, a fuel pressure regulator, and injectors.

Once installed, connect your tuning software, fine-tune the system, and enjoy improved reliability, throttle response, and the potential for serious power gains. Those old D-Jetronic or CIS parts? Box them up and embrace the future.

Have questions or need help selecting parts? Contact us at support@pmbperformance.com or call (855) 786-7101. Let’s bring your Porsche into the modern era!