It was designed and manufactured by the company "Française de Mécanique", a joint venture created by Peugeot (as predecessor to Groupe PSA) and Renault in 1969, and built in Douvrin in northern France.

It was an all-aluminium alloy SOHC inline-four design with two valves per cylinder driven by a chain, using petrol as fuel.

The integral transmission is mounted on the rear side of the crankcase (thus appearing to be underneath the power unit when it is mounted in the vehicle), and is driven by transfer gears which give a distinctive "whine" — a trait shared with the BMC A-Series engine, which uses a similar construction.

The X was used until 1990 in PSA vehicles — Renault discontinued the unit in 1982 when it reverted to its own Cléon-Fonte engine powerplants when the R14 was replaced by the R9/R11.

It was replaced in PSA vehicles by the more modern belt driven camshaft TU which was introduced in 1986 in the Citroën AX.

The 90 PS (66 kW; 89 hp) could be found in the Peugeot 104 ZS Coupé and Talbot Samba Rallye, and their respective racing versions.

The 72 PS (53 kW; 71 hp) variant could be seen in deluxe versions of these models, such as the Samba Cabrio and 205 XT, the Citroën BX and the Renault 14 TS.

The 80 PS (59 kW; 79 hp) version was reserved for the intermediate sports levels Visa GT, 205 XS/GT, Samba S and the 104ZS.