Rare Rides Icons: The Cadillac Eldorado, Distinctly Luxurious (Part LXVI)

The tenth generation Eldorado was updated in almost every way over its predecessor, turning the model into a much more modern personal luxury coupe in 1979. Our previous two Rare Rides installments reviewed the new-for-1979 Eldorado’s sleek exterior and its interior accommodations. After its debut, American car manufacturers’ tradition dictated it would be visually updated annually to keep sales flowing, but GM had other ideas.

The Eldorado arrived at a turning point for product and design philosophy at General Motors. Under newly appointed design director Irv Rybicki, the company’s new philosophy could be summed up very easily: save money. Annual visual updates were not considered cost-effective, so they went by the wayside. Changes during the tenth-gen Eldorado’s tenure were largely limited to the mechanical and electronic. American car buyers in general could no longer expect annual visual updates from the early Eighties onward.

In 1980 the Eldorado was updated in a big way with new electronic systems. The 1979 model arrived with an analog ECU and fuel injection (marketed as electronic fuel injection), and both were replaced the following year. There was an all-new electronic fuel injection (EFI), which Cadillac marketed as “Digital EFI,” controlled with an electronic ECU. The system was exclusive to Cadillac models that year.

Like other EFI systems that arrived through the Eighties, there were electronically-controlled injectors and the engine was monitored via an electronic computer processor. The system kept track of several variables to ensure precise fuel and air mixture, and it was promised the microprocessor would even compensate for parts of the engine as they aged.

The new electronics included on-board diagnostics systems that could be used by a mechanic to nail down issues very quickly. As other pre-OBDII systems, a series of button presses in the Eldorado would result in a flashing error code, then cross-referenced to a service manual. In case it failed, Eldorado had a backup old school analog computer that supplemented the electronic computer. Cadillac’s digital EFI would later be used across the GM range.

For 1980 there were three different engines available on the Eldorado. The 5.7-liter (350 cu. in.) diesel V8 was carried over from 1979. Also carried over was the old 5.7-liter Olds V8 with old style EFI, fitted only in California. Standard on Eldorado outside California and optional for Seville was a new 6.0-liter (368 cu. in.) V8, with fancy digital injection. For the rear-drive Fleetwood Brougham, DeVille, and Limousine, the 368 engine was standard but used a four-barrel carburetor.

The new 368 was a shrunken version of the old 500 cubic inch V8, and family member of the 425 and 472 engines. The 368 replaced all usage of the 425 in 1980, and the 425 was discontinued. A smaller displacement was required to meet CAFE economy requirements. The new Digital EFI was based on throttle-body fuel injection, rather than the multi-port layout of the previous analog EFI of 1979. 

Though it was a more modern injection system, the cut in displacement meant power in the Eldorado dropped to a measly 145 horsepower from its 6.0 liters. Torque was a more respectable 270 lb-ft, but not especially impressive. Rear drive models with the 368 had 150 horses via the carb.

In 1981 Cadillac debuted a disastrous change to its engine lineup when it made cylinder deactivation a standard feature on all gasoline V8 engines. Dubbed the “V8-6-4,” the technology used an all-new engine control unit (ECU) that allowed the engine to run on eight, six, or four cylinders depending upon driving conditions. The ECU was developed in conjunction with Eaton Corporation.

Cadillac’s marketing said it was “like three engines as one,” as the engine’s Modulated Displacement would automatically determine which number of cylinders was appropriate while in motion. Praised immediately as a technological watershed moment, the implementation of the technology proved troublesome. There were issues reported by consumers almost immediately as they drove their vehicles in ways different to Cadillac engineers’ specific testing environments.

In short, the ECU was limited in what it could process and its processing speed. With driving conditions that changed constantly and numerous variables, the computing power of the ECU could not hope to keep up. Additionally the engine’s manual EGR valve used positive backpressure, which failed to operate properly on the exhaust gases in four-cylinder mode. This caused engine ping.

There’s much more detail to the V8-6-4 debacle, but we’ve covered that extensively in an Abandoned History series you can read here. The engine technology was so bad it lasted only a single model year before it was dropped. 

An additional engine was available in the Eldorado from 1981 to 1982, the 4.1-liter Buick LC4 V6. A bit of sacrilege, it was the first six-cylinder engine ever offered in a Cadillac. General Motors added it to Cadillac’s lineup as it pursued more CAFE credits. Equipped with a four-barrel carburetor, the V6 made 125 horsepower and 205 lb-ft of torque.

Engine revisions didn’t stop there, as in 1982 an all-new V8 arrived. The anticipated “High Technology” engine, more commonly labeled as the HT4100. With 4.1 liters of displacement, it was designed for use with front-drive vehicles. It managed 135 horsepower which meant a 0-60 time in the Eldorado of 13.8 seconds. 

HT4100 was rushed into production for 1982 because the V8-6-4 of 1981 was such a disaster. As a half-baked development project, the engine paired cast iron heads to its aluminum block. Blocks were poorly and unevenly cast, head bolts pulled from their threads, gaskets failed, cam bearings failed, and aluminum oil pumps went belly up quickly. Full detail on the HT4100 is available via Abandoned History, here.

Unlike the V8-6-4, Cadillac would not bail on the HT4100 because they didn’t have another engine option. Customers did not accept a Buick V6 in a full-size Cadillac, the diesel V8 was a flop, and engines like the 368 were not compliant with upcoming emissions regulations. The HT4100 would be refined, massaged, enlarged, and rebranded. 

It became a respectable engine in its own right eventually as the “4.5-liter Cadillac V8” with nary a mention of High Technology. It was then further refined into the 1990s where it entered its final iteration as the 4.9-liter V8. During all its engine issues, consumers held an eager appetite for the Eldorado. Later in the generation, the Eldorado debuted the special Touring series of vehicles that Cadillac would persist in creating through the 2000s. We’ll pick up there next time.

[Images: GM, seller]

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