By 1981, GM, Ford and Chrysler were using using microprocessors to help their new vehicles meet ever more stringent federally mandated emissions and fuel economy standards. Through a series of sensors detecting throttle position, coolant temperature, manifold pressure and RPM, these primitive analog computers did an admirable job of helping The Big Three achieve government requirements. That doesn't mean these early computer-controlled automobiles actually ran very well.
Cadillac, naturally if not arrogantly, took things several steps further and had GM's "Computer Command Control" manage not only emissions control but fuel injection; all other GM divisions were still using carburetors. What's more, a fuel injection system that would control the operation of cylinder banks on their large V-8 engine to help Cadillac improve fuel economy. Essentially a cylinder deactivation or displacement on demand system they called, "V8-6-4".
Depending on vehicle load, the engine would use four, six or as many as eight of its cylinders. Solenoids engaged blocker plates that stopped the rocker arms from engaging the intake and exhaust valves. Air was pumped into the cylinders not being used to cushion any sensation of a misfire. Cadillac claimed a 15 % fuel economy increase for the V8-6-4 compared to the same engine without it. Back in the early 1980's going from 14 miles per gallon to almost 17 being cause for celebration.
Now, if GM cars with "Computer Command Control" that had a carburetor had idled strangely and stumbled and hesitated when accelerating, imagine how poorly a far more complex fuel injected car ran. Not only that, but a fuel injected car where banks of cylinders turned on and off. Mechanically, the engine was fine; it was the "Computer Command Control" that couldn't keep up with myriad driving scenarios regardless of the fact that GM claimed the computer could handle up to 300,000 calculations per second.
Note the very tall valve covers on the V8-6-4; extra room for the blocker plates to move up and down. The solenoids that triggered them are on top of the valve covers.
Displacement on demand or cylinder modulation is fairly commonplace today and even today's engines stumble or vibrate somewhat going between cylinder modes. Again, with the computing power of the early GM computers, the V8-6-4 didn't just stumble between modes, it all but tripped and fell down. The V8-6-4 got stuck in four or six-cylinder mode, made the engine vibrate harshly and at worst the engines would not start at all. A deluge of recalls to fix the problems became a public relations nightmare for Cadillac and General Motors. To make matters worse, the V8-6-4 was the standard engine on all deVilles and Fleetwoods for 1981. That was a lot of recalls.
Customers either had the V8-6-4 disabled, the entire system removed and replaced with a carburetor or the "Computer Command Control" reflashed and updated. Either way, it made for an expensive day at the office for Cadillac and General Motors. Our painfully original subject here still has her V8-6-4 system and the seller of this car claims it runs very well. I wasn't about to ask questions about whether it was still hooked up or if the computer had been updated. Some things are best to speculate about. Most "V8-6-4" Cadillacs from back in the day that I knew had the system "turned off". Apparently, turning it off was as simple as disabling the solenoids on top of the valve covers.
Interestingly, Cadillac did not develop the V8-6-4 further. Instead, they replaced the engine with something arguably worse, the aluminum block, iron head, "HT4100". Why they didn't simply use Oldsmobile's unspectacular but bulletproof 307 engine in these cars or, heaven forbid, the Chevrolet 305, is anyone's guess. While it's easy to armchair quarterback thirty-six years later as to what Cadillac should have done, it's impossible to say with any certainty that what they should have done would have been any better than what they did.
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