an endless duplex hydraulically tensioned timing chain was used to drive the overhead cams. The chain measured . The casting and bearings for the standard underhead cam were repurposed for a shaft which drove the oil pump. Ignition was controlled by an EDIS-6 system, which would become a standard feature. The engine was known for its substantial increase in power delivery above 4000 rpm relative to the unmodified version; in recent years, the engine has become a popular choice as a replacement engine for the Ford Sierra XR4x4 and XR4i. An improved version of this engine (code BOB) was available in the restyled 1995 Ford Scorpio. Differences included two simplex chains with two hydraulic tensioners and the addition of a variable-length intake system called VIS. Power output was increased to . This was mated to a fully electronically controlled A4LDE automatic transmission. 4.0 The pushrod , with a bore and stroke version, although produced in Cologne, Germany, was only fitted to American vehicles. The OHV engine was produced until 2000 and was used in the Ford Explorer, Ford Aerostar, Mazda B4000, and Ford Ranger. Output was and . Though some variation exists, typically is quoted as horsepower for 1990–92 applications. Applications: Ford Ranger/Mazda B-Series Ford Explorer/Mazda Navajo Cross Lander 244X Ford Aerostar (1990–1997) SOHC The SOHC version was introduced in 1997 in the Ford Explorer, alongside the original pushrod version. It features a variable length intake manifold and produces and f. (The variable length intake manifold was discontinued in 1998, replaced by a standard intake.) It uses a jackshaft in place of a camshaft to drive a timing chain to each cylinder head. Three timing chains are used, one from the crank to the jackshaft, one in the front of the engine to drive the cam for the left bank, and one on the back of the engine to drive the cam for the right bank. In addition, the 4WD Ranger with the SOHC 4.0 had a 4th timing chain driving what Ford called a balance shaft. Ford has since phased out the engine in favor of the more powerful and efficient Duratec 37. Timing chain problems The 4.0 SOHC engine was notorious for the OEM timing chain guides and tensioners breaking, resulting in timing chain rattle or "death rattle". This problem can occur as early as in some vehicles. Due to the SOHC engine's unique design involving both front