1984 Cadillac Coupe DeVille - Aero Pixie Dust

I loved the aero pixie dust Cadillac sprinkled on their 1980 deVilles and Fleetwoods and in particular what they did with the Coupe deVille. While still angular and undoubtedly "Cadillac", those angles were softened making the design more cohesive and making the cars appear larger; size being very important to Cadillac buyers back then. However, the "updates" under the hood, indirectly mandated by government fuel economy standards, where less than enthralling.

Those federally mandated fuel economy standards coming in the wake of the 1973-74 OPEC embargo. "Corporate Average Fuel Economy", also known as "CAFE", first established in 1975, set the average new vehicle fuel economy, as weighted by sales, that manufacturers fleet had to achieve. The first CAFE regulations went into effect in 1978 where manufacturers had to achieve a CAFE of 18 miles per gallon. It increased to 19 for 1979, 20 for 1980 and 22 mpg for 1981; quite a jump in just four years. While The Big Three had already either made their makes and models smaller and lighter or were well on their way towards doing so, it would take more than downsizing for them to achieve the fuel economy averages the government ordered.

That meant a change to computer controlled engine management systems and ultimately to fuel injection.  GM's first real mass market attempt at fuel  injection was in 1976 when Cadillac modified the Oldsmobile Rocket 350 engine with a fuel injection system they co-developed with Bendix and Bosh.  Consisting of a throttle body, 8 fuel injectors on fuel rails and controlled by an analog computer, while far from perfect, it operated much better than the Rochester mechanical fuel injection system GM experimented with between 1957 and 1962. General Motors "digitized" the computer, what they called the "ECM" (electronic control module) for 1980 and by 1981 had enabled the version of it they offered on Cadillacs to control not just fuel injection, but to turn cylinders on and off depending on vehicle load.

Chevrolet and Pontiac had first offered fuel injection in the late 1950's but it was expensive and its crude electronics made it problematic. Chrysler also offered a fuel injection system in the late 1950's that was even more troublesome. Ford waited until the late 1970's to offer fuel injection on anything they manufactured.

What they called the "V8-6-4", theoretically, worked via solenoid deactivation of the engine's rocker arms and different fuel mapping when in four and six-cylinder operation. While it improved fuel economy and helped GM hit the government's lofty 22 mpg goal for 1981, particularly when moving into and out of six-cylinder mode, the engine stumbled, bogged and vibrated harshly. Rather unbecoming of any automobile to say nothing of a Cadillac. Most owners of 1981 Cadillac's V8-6-4's either had the system turned off or replaced with a carburetor. For 1982, rather than refine the V8-6-4, Cadillac replaced it with an engine even more disastrous than the V8-6-4.

Now, the answer to the question as to why Cadillac didn't simply install the Oldsmobile 307 V-8 or Chevrolet 305 in the deVille and Fleetwood after the V8-6-4 debacle requires us to understand GM's myriad divisional brand essence. In retrospect the practice was ludicrous but to help distinguish, for instance, a Chevrolet from a Buick and Pontiac from a Cadillac, all of GM's divisions designed and built their own engines. Regardless of the fact that all the divisions, with the exception at times of Cadillac, shared so much sheet metal with each other that it was difficult to tell a Chevrolet from an Oldsmobile. With these self-imposed restrictions, though, and with the V8-6-4 drowning in recalls, what Cadillac did next, on paper at least, was quite clever; in practice it nearly killed them off.

Starting in 1982, Cadillac took the little V-8 they were developing for their front wheel drive "big" cars, slated for introduction originally in 1983, and adapted it to rear wheel drive. They called the engine the "HT4100" and it was a disaster. Making only 135 horsepower, 190 foot pounds of torque and having to move a two ton automobile, drivability issues were the least of the problems that buyers had with the "HT4100"; "HT" incidentally was for "high technology". The problem was the HT's aluminum block and iron head design. This unusual design was prone to intake manifold gasket failure due to scrubbing of the bi-metal interface. Its aluminum oil pump also failed regularly, cam bearings gave way with no notice and weak bolts pulled their aluminum threads from the block. All this meant more recalls. Recalls meant more bad P.R. for Cadillac. While it's been said that any P.R. is good P.R., with regards to Cadillac in the early 1980's, the problems with the HT was just another gut punch.



Remarkably, Cadillac continued to refine the HT over the years eventually making it into a very good engine. The last Cadillac to be powered by an HT left factories at the end of the 1995 model year replaced by another head gasket devouring Cadillac  fiasco, the "Northstar".

By 1984, Cadillac had engineered out most of the issues with the HT4100 and our lovely subject here was originally built with one. While Cadillac made the HT4100 more reliable, they never improved drivability since they only marginally increased the amount of horsepower and torque it made. Shame too; these were such a pretty cars. While most domestic luxury cars in the early 1980's were under powered these big Cadillac's with the tiny HT were particularly slow and unresponsive. Nothing that an engine swap couldn't fix though, right?

Well, ask and ye shall receive. I don't know what I was searching Craigslist for recently but low and behold, down in Columbus, I came across this listing for a 1984 Coupe deVille powered by a mid-1990's, GM LT-1. What's more, it looks professionally done and looks complete. The writer of this ad, https://columbus.craigslist.org/cto/d/1984-caddilac-coupe-deville/6295155023.html, claims the transmission's been swapped too; no idea about the rear axle being updated to something more stout than what was originally stock. The ad also claims the engine is from a 1995 Corvette. I highly doubt that and points off for credibility for claiming so if it isn't. This looks more like the LT-1 that was found in the Cadillac Fleetwood, Buick Roadmaster and Chevrolet Caprice and Impala SS of that vintage. It's more than just a matter of semantics to say that this is a "Corvette" engine; there's enough different between the Corvette LT-1 and this LT-1 to say that this engine should have been called something else. Still, this LT-1 was a robust and powerful engine. Especially compared to the HT.

So, why am I not running down to Columbus to at least kick the tires on this sexy beast? Well, for starters, Columbus is a haul from Cleveland and while this car is listed in the Columbus Craigslist it's actually about an hour east of Columbus which means it's close to three hours from me. That's a precious weekend day shot just to joyride, with little to no intent of buying, a hopped up thirty some odd year old Cadillac that has some middling issues. The speedomoter doesn't work, the vinyl top is shot and look at that right front fender in front of the tire; rust bubbles. All fixable but, at least with regards to the vinyl top and fender, expensive to fix. And who knows what else there is wrong with this thing. Again, she's 30+ years old.

There's also the asking price of $6,000. That's a lot for this car. I mean, a ton. It makes some sense, though, when you think about all that you would be getting with it. Although the transplanted engine is "just' an LT-1 and not a far superior LS, the upside is the HT4100 has been removed. From these pictures this could be a pretty good $1,800 car if it had the HT4100 and closer to $2,500 if not $3,000 if the top and body was perfect. Factor what it would run you to swap out the HT and drop in something better would run at least $2,000 if not $3,000. An LS-1? $5,000-$6,000. At least. What's it they say about buying someone else's project rather than pay for it yourself? Thing is with this car, at six grand, it appears you'd be paying for all the freight. This car is no bargain.

Like almost all older GM small blocks, the Generation II LT-1 gets leaky as its gets older. Again, fixable but at a cost. The GM LS series is so much better but then, again, if this car had an LS it probably would have an asking price three if not four grand higher. Hit that link above and have at it. I'll be jealous as hell you did too especially if you can talk them down to close to $4,000 as this car is just about as perfect a "1980" aero pixie dust Coupe deVille as you're ever going find.

From 1986-1991, Cadillac offered the Oldsmobile 307 cubic inch V-8 in their rear wheel drive Fleetwood Brougham.