Archive for the ‘L62’ tag


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1981 Cadillac Coupe Deville C5006-0008
1981 Cadillac Coupe de Ville. Photo courtesy GM Media Archive.

Variable-displacement engines are used by a variety of manufacturers today, including Mercedes-Benz, General Motors, Chrysler and Honda, but the idea of deactivating cylinders to improve fuel economy under constant throttle conditions isn’t a new one. In fact, it dates as far back as the early years of the 20th century, when the Sturtevant 38 allowed motorists to shut down as many as three cylinders to save fuel.

Today’s variable-displacement engines operate seamlessly and deliver reliability on par with more conventional designs, thanks to sophisticated engine management systems. That wasn’t the case before electronics technology matured, and Cadillac will forever be known as the company that launched the forward-thinking but trouble-prone L62 V-8-6-4 engine in its 1981 model lineup.

In the opening years of the 1980s, automakers struggled to meet more stringent Corporate Average Fuel Economy (CAFE) requirements, brought on by a new round of fuel shortages in 1979. In 1980, Cadillac downsized its 425-cu.in. (7.0-liter) V-8 to 368 cubic inches (6.0 liters), then added throttle-body fuel injection to passenger models in an effort to increase fuel economy. This engine, dubbed the L61, didn’t produce the fuel savings that designers had hoped for, so for 1981 Cadillac introduced another new engine, called the L62, that promised to revolutionize the automotive industry. Cadillac was so confident in its design that the L62 was standard equipment throughout the automaker’s 1981 model range, except for the Seville where it was an available option to replace the standard diesel V-8.

1981 Cadillac-04
Images courtesy OldCarBrochures.com.

Developed in conjunction with automotive supplier Eaton Corporation, the L62 V-8 had a rather unconventional feature called “modular displacement;” under reduced load conditions, cylinders were automatically deactivated to make the engine a 4.5-liter V-6 or even a 3.0-liter V-4, thus reducing fuel consumption (and improving GM’s CAFE numbers). The advanced system relied on data like engine speed, EGR position, intake manifold air pressure and air pump operation to determine a constant-throttle condition (such as cruising on the highway), in which case the Computer Command Module would shut down two or four opposite-bank cylinders. The driver would see a digital “MPG  Sentinel” indicator on the dash, showing how many cylinders were still in use or displaying instant miles-per-gallon data.

Mechanically, Cadillac’s system used solenoids to disengage the rocker arms on affected cylinders, keeping their intake and exhaust valves closed. Compressed air in the deactivated cylinders acted as a cushion to reduce the sensation of the engine misfiring, and also served to keep cylinder temperatures elevated for quicker ignition on demand, when the driver stepped on the gas. Cadillac assured buyers that the change in displacement would be nearly imperceptible, and that a 30 percent increase in highway fuel economy would be worth the penalty of a slight hesitation as the engine transitioned from a V-4 or a V-6 to a V-8.

Image courtesy OldCarBrochures.com.

In addition to this futuristic fuel-saving technology, the L62 V-8-6-4 also brought with it advanced diagnostic capabilities, allowing mechanics to view some 45 trouble codes via the MPG Sentinel or HVAC display without  the use of external code scanners. Technicians could view captured diagnostic codes, get live sensor readings and even cycle the solenoids related to the cylinder deactivation system, years before such sophisticated remote diagnostics became commonplace.

Though the mechanical components of the L62 V-8-6-4 may have been sound, the system’s electronics were not. Despite Cadillac’s claims that the Computer Command Module could process some 300,000 commands per second, it lacked the programming sophistication and overall speed necessary to direct the system across all driving conditions. Cadillac released some 13 updates, all via EPROM chip, for the Command Control Module, but none managed to overcome the system’s insurmountable obstacles. For 1982, Cadillac returned to a conventional V-8 engine design (now further downsized to 4.1-liters) for its passenger car range, while most owners of L62 V-8-6-4 Cadillacs simply had the cars converted to full-time V-8 power.

1981 Cadillac 6.0 Liter V-8-6-4 Variable Displacement Engine B4006-0270
The GM L62 V-8-6-4. Photo courtesy GM Media Archive.

Though the ill-fated L62 engine lasted just a single production year, the range of 1981 Cadillac passenger car models foretold the future of modern variable-displacement V-8 and V-6 engines, as well as the future of onboard vehicle diagnostics. Modern pushrod engines of variable displacement typically use hydraulic lifters to shut down cylinders by reducing the oil pressure to the desired lifter. Contemporary variable-displacement overhead cam engines generally use a solenoid mechanism to lock or unlock a pair of linked rockers, where one opens and closes the valve while the other is moved by the camshaft.

Neither design is more mechanically sophisticated than the Cadillac and Eaton system from the early 1980s, but modern electronics allow for much more sophisticated engine management (and thus, system control). When one considers the difference in personal computing power from 1981 today, it really does demonstrate just how ambitious GM’s engineers were in implementing the L62 engine. Fortune, however, does not always favor the bold.