My vote goes for either the 2.7 Mopar or the 3.5 that was in the original LH cars (re 93 Concorde). Only because I owned both of these engines. The 3.5 went through timing chains and water pumps every 20,000 kms and the problems with the 2.7 have been welle doccumented on this forum.
Here are a few other designs that should have been left on the drawing board.
In 1981, engineers at Cadillac made an attempt at producing better gas mileage for its line of heavy luxo-liners. Dubbed the V8-6-4 (or, Displacement On Demand), the engine changed cylinder modes, eliminating two cylinders at a time as power demands decreased. The idea was right on the money, but the available technology to implement it was not. Measuring 368 cubic inches, oil pressure to specially-designed hydraulic lifters was shut off by solenoids, which caused the lifter to collapse, and effectively prevented the cam lobe from opening the related valve. The biggest rap with the V8-6-4 was a distinct hesitation when cylinders were deactivated, which commonly became known as a "driveability" problem. The same engine resurfaced in 1982, without its cylinder deactivation feature, and as a result, was generally considered to be a good engine.
MOPAR 2.2L I-4
Launched with the successful K-Car line, the Mopar 2.2 soon became known as a rod-knocker. With multiple failures rolling in, Mother Mopar did the unthinkable and added a turbo to it. This may have been okay if it had remained under the hood of only the specialized Shelby GLHS and Dodge Daytona (quite swoopy FWD cars at the time), but Mopar chose to share the love across the entire product line--from the full-size Chryslers (also FWD) to the insanely-popular minivans. Literally, millions of Turbo 2.2 engines were produced, and while many survived, a good percentage caused headaches for owners and service techs alike. Interestingly, when rebuilt for high performance, the 2.2 has proven to be a solid foundation. However, in stock shape, their ill reputation remained.
OLDSMOBILE 350 DIESEL
The GM Corporate partners shared the grief associated with its diesel debacle of the early '80s. More often considered an Oldsmobile motor, this converted gasoline engine was used throughout the GM family, and even found its way into top-of-the-line Cadillacs, with disastrous results. Failures were commonplace, often including internal engine components. At the time, mechanics and service writers referred to warrantee repair orders as "A.F.A." - or Automatic Factory Acceptance, and each respective franchise had mountains of repair orders related to the 350 cid diesel.
CHEVY 2.2L I-4
Recently replaced by the all-new Ecotec 2.2, this pre-Ecotec inliner was a disaster. Lacking in power, unreliable, and hungry for head gaskets, the anemic four was offered in many GM front-drivers (like the Beretta and Cavalier), and the popular line of Chevy S-10/GMC S-15 pickups. Press reviews at the time recommended against backing these engines with automatic transmissions, especially in the pickups. With pathetic power and unreliable durability, what could be worse? A series of steel freeze plugs were also known to corrode, providing a messy time bomb that could go off at almost any mileage reading past 50,000. It's no wonder GM used absolutely no engineering or design from this engine when developing the Ecotec. We think GM should offer Ecotec upgrades to all owners of these pathetic mills, but alas, the designs have so much variance between them, swaps are no easy task. Too bad.
FORD 2.8L V-6
Offered in the downsized Mustang and Capri, as well as Ranger pickups, the Ford 2.8 remains a rickety memory. With a double-barrel reputation based on its noisy solid-lifter valvetrain and cracked cylinder heads, the 2.8 should be commended only for offering World Products the ability to profit from its shortcomings. When World chose to build all-new Ford V-6 heads as replacements for the factory parts, we doubt even they could have predicted it would become their most-popular seller. In a product line armed with some of the best aftermarket performance cylinder heads ever cast, the lowly Ford 2.8 V-6 replacement outsold 'em all. That should tell you how bad the factory design was.
VEGA 140 OVERHEAD CAM
This one was in production from 1970 to 1977. At the time, John Delorean was on Chevy's executive team, and had reportedly commented that the design of this engine resembled a pre-war tractor motor. Though some are not aware, this little "four-lunger" featured silicone-impregnated aluminum cylinders - not cast-iron sleeves, like most aluminum blocks. Early in production, Chevy re-called some 132,000 vehicles to correct the possibility of a carburetor fire. Other design characteristics were displayed as the blocks were subject to distortion, due to overheating, and the cylinders were prone to wear, causing an unusually high oil consumption.
Once again, we called on our 84-year-old automotive historian from Connecticut, whose tack-sharp memory immediately recanted snippets from days gone by. Beginning in 1940, the Lincoln V-12 was developed under orders from Henry Ford. Its basic design elements were borrowed from Ford's existing V-8, though the V-12 was engineered with a 75-degree angle. Surprisingly, it produced an approximate 110 to 120 horsepower, despite being abundant in cylinders. Like many early powerplants, overheating problems ensued, causing warped cylinders and excessive oil consumption. Likewise, early versions suffered from poor crankcase ventilation, resulting in dreaded sludge buildup. Later, engineering changes offered a much improved crankcase ventilation system, and also featured hydraulic lifters for quieter and more reliable operation.
Cadillac strikes again. This time, it was an attempt at developing a lighter-weight, 4.1 liter engine called the HT4100. This engineering marvel featured an aluminum block, and for reasons unknown, cast iron cylinder heads. Displacing a paltry 249 cubic inches, it produced a meager 135 horsepower at 4,400 rpm. Many of its woes were related to failed head gaskets, which allowed coolant into the crankcase. Naturally, that chain of events resulted in GM supplying tons of crankshafts, camshafts, and related hardware under the AFA program. Even when they ran, the HT4100 was grossly underpowered. As a result, Cadillac suffered in sales and stature, conditions that took several years to overcome