The Porsche 944 uses an electronic fuel injection system made by the Robert Bosch company called “Motronic”. This system is also referred to as a “DME” or Digital Motor Electronics. It was a huge step forward over older “D-Jet” and “L-Jet” fuel management because it electronically controlled both fuel and spark using a digital computer. This created a much better-behaved engine by improving power, fuel economy, drivability and emissions. The 944 was introduced in 1982 with the Motronic v2.1 system (ML2)
In 1985, Porsche released a major update for the 944, including a turbocharged model. Both the Naturally Aspirated (i.e. NA) and Turbo 944 (i.e. 951) received basically the same Motronic 3.1 (ML3) system that was already equipped in the 911 3.2L Carrara. However, the 951 required electronic boost regulation and more advanced ignition control. This is because the increased cylinder pressure of the turbocharged engine produces “knock” which can lead to severe engine damage. This issue was solved by a second engine computer commonly known as the “KLR” but also as “KCP” or “Knock Control Unit.” The KLR regulates boost pressure and can override the DME’s ignition signal to retard the ignition advance when it senses the onset of engine knock.
Later in 1987 and 1989 Porsche introduced the “S” and “S2” models respectively for the 944 NA which were equipped with more powerful 16-Valve engines. These higher performance engines meant higher combustion pressure making engine knock a significant issue. This is where Porsche introduced the Bosch Motronic v4.x (ML4) DME with integrated knock control. Unlike the ML2 and ML3 computer, the ML4 does not share the same connector. This is because the knock controller requires several more pins that are simply not available on the older DME’s.