Slumping sales of the 911 seemed to confirm that the model was approaching the end of its economic life cycle. Fuhrmann envisioned the new range-topping model as being the best possible combination of a sports coupe and a luxury sedan, something well equipped and comfortable enough to be easily driven over long distances that also had the power, poise and handling prowess necessary to be driven like a sports car. This set it apart from the 911, which was a pure sports car. Ordered by Ferry Porsche to come up with a production feasible concept for his new model, Fuhrmann initiated a design study in 1971, eventually taking from the process the final specs for the 928. Several drivetrain layouts were considered during early development, including rear and mid-engined designs, but most were dismissed because of technical and/or legislative difficulties. Having the engine, transmission, catalytic converter(s) and exhaust all cramped into a small rear engine bay made emission and noise control more difficult, something Porsche was already facing problems with on the 911 and wanted to avoid.
After deciding that the mid-engine layout didn't allow enough room in the passenger compartment, a front engine/rear wheel drive layout was chosen. Porsche also feared at the time that the U.S. government would ban the sale of rear-engined cars in response to the consumer outrage over the Chevrolet Corvair, started by Ralph Nader via his book "Unsafe at Any Speed". Porsche engineers wanted a large displacement motor to power the 928, and prototype units were built with a 5.0 Ltr V8 producing close to 300 hp (220 kW). Very early units used one four-barrel carburetor, which was eventually tossed in favor of Bosch's K-Jetronic fuel injection system. When increasing concern within the company over the pricing and availability of fuel during the oil crisis of the 1970s became an issue of contention, smaller engines were considered in the interest of fuel economy. Some managers began pushing for development of a 3.3 Ltr 180 hp (130 kW) powerplant they had drawn up specs for, but company engineers balked at this suggestion. Both sides finally settled on a 4.5 Ltr, SOHC 16-valve V8 producing 240 PS (237 hp/177 kW) (219 hp (163 kW) in North America), which they considered to have an acceptable compromise of performance and fuel economy.
The finished car debuted at the 1977 Geneva Motor Show before going on sale later that year as a 1978 model. Although it won early acclaim for its comfort and power, sales were slow. Base prices were much higher than that of the previous range-topping model and its larger size and somewhat odd futuristic styling put off many purists who were more attracted to the more compact 911. Fuhrman's replacement, Peter Schutz, decided that the models should be sold side by side, feeling that the 911 still had potential in the company's line-up.
Legislation against rear-engined vehicles also didn't materialize.
Although the 928 developed an avid fan following, it never sold in the numbers that Fuhrmann had originally predicted and was discontinued in 1995.