Volvo went from Djet, Ljet, Kjet (80-82) and then immediately dumped Kjet in favor of LH 1.0-3.1 from 83-93. By 89 they were using knock sensors with 10:1 CR on 87 gas. Those systems were perfectly reliable. I don't know why mercedes stuck with Kjet for 15 years right up to Motronic.