 The fuel pumps can be either driven by an extra camshaft lobe or by an electrical supply where each pump unit is connected to the injector via a short precise length high-pressure fuel line as opposed to Unit Injector systems which combines both a pump and an injector element in a compact unit.Both systems feature electronically controlled fuel solenoids for precise timing and the injection of fuel quantity is variably adjusted for each cylinder.Known commercial vehicle manufacturers using the system are Mack (discontinued), Liebherr,Mercedes-Benz, its subsidiaries Freightliner, BharatBenz and Western Star, by Detroit Diesel made MBE 4000 engine.