from wikipedia so dont crucify me if its not accurate:
"For 1981 Cadillac introduced a new engine that would become notorious for its reliability problems (with the electronics, not the robust mechanical design), the V8-6-4 (L62). The L61 had not provided a significant improvement in the company's CAFE numbers, so Cadillac and Eaton Corporation devised a cylinder deactivation system called Modulated Displacement that would shut off two or four cylinders in low-load conditions such as highway cruising, then reactivate them when more power was needed. When deactivated, solenoids mounted to those cylinders' rocker-arm studs would disengage the fulcrums, allowing the rockers to "float" and leave the valves closed despite the continued action of the pushrods. These engines are easily identified by their rocker covers, which each have elevated sections over 2 cylinders with electrical connectors on top. With the valves closed the cylinders acted as air-springs, which both eliminated the feel of "missing" and kept the cylinders warm for instant combustion upon reactivation. Simultaneously, the engine control module would reduce the amount of fuel metered through the TBI unit. On the dashboard, an "MPG Sentinel" digital display could show the number of cylinders in operation, average or instantaneous fuel consumption (in miles per gallon) or estimated range based on the amount of fuel remaining in the tank and the average mileage since the last reset.
Another rare and advanced feature introduced with DFI was Cadillac's truly "on-board" diagnostics. For all those mechanics who had to deal with the 368's, the cars contained diagnostics that didn't require the use of any special external computer scan-tool. The new Electronic Climate Control display, along with the MPG Sentinel, provided on-board readout of any stored trouble codes, instantaneous readings from all the various engine sensors, forced cycling of the underhood solenoids and motors, and on the V8-6-4 motors, manual cylinder-pair control. The L62 produced 140 hp (104 kW) at 3800 rpm and 265 lb·ft (359 N·m) 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 teething problems. The biggest issue was that the Engine Control Module simply lacked robustness, and the programming & processing speed to efficiently manage the cylinder-deactivation under all load conditions. 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 production cars - it lasted until 1984 in the limousines. All rival big blocks disappeared between 1976 and 1978. In the RWD models it was always coupled with the heavy duty THM400 transmission, the last factory-produced GM car to come with this"
but Im just trying to see if others have looked into these things before me... 
