trouble codes, instantaneous readings from all the various engine sensors, forced cycling of the underhood solenoids and motors, and on the V8-6-4 engines, manual cylinder-pair control. The L62 produced at 3800 rpm and at 1400 rpm. Cadillac hailed the L62 as a technological masterpiece, and made it standard equipment across the whole Cadillac line. While cylinder deactivation would make a comeback some 20 years later with modern computing power (and using oil pressure to deactivate the valves by collapsing the lifters) Cadillac's 1981 V8-6-4 proved to have insurmountable engineering problems. The main issue was that the Engine Control Module simply lacked the robustness, programming and processing speed to efficiently manage the cylinder-deactivation under all load conditions. In the era before electronically operated EGR valves, the engineers also made an error in using a "back-pressure-type" EGR valve. While this early effort to match the vacuum-controlled EGR volume more accurately to the engine's load made sense in a 'normal' engine, it had the effect of causing pinging (detonation) problems in the V8-6-4 engine, because 4 cylinders operating under higher load needed more EGR, while they were actually producing less exhaust flow and therefore less back-pressure to operate the valve. In an effort to increase reliability, Cadillac issued thirteen updated PROM chips for the ECMs, but many of these engines simply had their Modulated Displacement function disabled by dealers, leaving them with permanent eight-cylinder operation. This was accomplished by merely disconnecting a single wire from the transmission's "3rd-gear switch", or running it through a switch inside the car for manual override. The 368 was dropped from most Cadillac passenger cars after the 1981 model year, although the V8-6-4 remained the standard engine for Fleetwood Limousines and the carbureted 368 remained in the Commercial Chassis through 1984. The 368 has the distinction of being the last traditional "big-block" cast-iron pushrod V8 engine available in a production car. It lasted through 1984 in the limousines. Rival big blocks, 396, 400 (Chrysler & GM), 402, 426, 440, 454, 455, 460, etc. disappeared between 1976 and 1978. RWD models were coupled with the heavy duty THM400 transmission, the last factory-produced GM passenger car fitted with this transmission. Cadillac High Technology engine The OHV Cadillac High Technology engine was produced from 1982 to 1995 in displacements of , , and . Northstar Cadillac's DOHC, four valves per cylinder Northstar debuted in 1992, its most technologically advanced engine ever.