engines was initially the only one offered in the US market, to help meet Corporate Average Fuel Economy (CAFE) requirements. The 380 SEL earned a poor customer perception in the United States as being severely underpowered and due to mechanical issues with the single timing chain. The 380 SEL for the US market took 11 seconds to reach from standstill and had top speed of . The severe performance shortcoming of W126 with V8 engine was addressed by introducing more powerful 500 SEL/SEC in 1984. The S-Class coupé was fitted with V8 engines only for the first time. The 3.0-litre five-cylinder inline OM617 diesel engine was carried over from W116 with same performance. The diesel engines were again never offered in the markets outside United States and Canada. This discrepancy wasn't addressed until 1994 when W140 S 350 Turbodiesel was introduced in Europe for the first time. In 1981, Mercedes-Benz introduced the Energiekonzepts ("Energy Concept") programme in reducing the fuel consumption. This programme revised the combustion chambers and piston heads with lower compression ratio in the V8 engines. This revision caused further drop in engine performance. Second Series (1986-1991) For the second series introduced in September 1985, the engine range was extensively revised with new six-cylinder inline engines and enlarged V8 engines. Only 5.0-litre M117 V8 was carried over from the first series, expanding the V8 engine range to three. The revised engine range focused more on reducing pollution and fuel consumption even further. For the first time, the customers outside US and Canadian markets could choose the models with or without catalysators. The models without catalysators can be retrofitted with catalysators at later date if the customers choose to: this retrofit method is called RÜF (Rückrüstfahrzeug — loosely translated as retrofit vehicle). The RÜF models had a mechanical switch in the engine bay to be operated by owners for running on lead or lead-free fuels, a necessary feature for driving outside Germany or in areas within Germany where the lead-free fuel wasn't widespread yet. In 1990, all engines were fitted with catalysators only and the mechanical switch eliminated. The new six-cylinder inline M103 engine had a single overhead camshaft and electronic-mechanical fuel injection and was available in two sizes: 2.6 and 3.0 litres. The carburetted engine fitted to 280 S was eliminated, marking the end of carburetted engines for S-Class, and replaced with fuel-injected engines for 260 and 300.