Several Volkswagen (VOWG_p.DE) engineers have admitted manipulating carbon dioxide emissions data, saying the ambitious goals set by former Chief Executive Martin Winterkorn were difficult to achieve, Bild am Sonntag reported. The paper said VW engineers tampered with tire pressure and mixed diesel with their motor oil to make them use less fuel, a deception that began in 2013 and carried on until the spring of this year. “Employees have indicated in an internal investigation that there were irregularities in ascertaining fuel consumption data.