The AJ6 (Advanced Jaguar 6-cylinder), and the similar AJ16, were inline-6 piston engines used by Jaguar cars in the 1980s and 1990s. The AJ6 was designed to replace the successful and long-used Jaguar XK6 engine, and was introduced in 1984. It was only the third all-new engine ever designed by the company. The AJ16 evolution was replaced in 1996 with the Jaguar developed AJ-V8 engine. Jaguar had considered cutting their existing V12 in half to build a V6, or possibly a V8, but chose instead to develop a new inline six. The cylinders are inclined, as in a slant-6, by 22 degrees. It uses an aluminium block to reduce weight, and has an optional DOHC head for higher efficiency and power. AJ6 The original engines were the DOHC 3.6 and the SOHC 2.9. The DOHC 3.6 was revised and enlarged to 4.0 in 1990. It is still essentially an "AJ6", however. This was, as per usual, offered for the XJ-S before it was built into the XJ40 saloon. 3.6 The was the first AJ6 engine, debuting in 1983 on the XJ-S. It had DOHC 4-valve heads with a bore and stroke. Power was with of torque. Power was reduced to for versions having catalytic exhaust system. Early versions of the AJ6 as used in the 1984 - 1987 XJ-S cars had a conventional distributor type of ignition system with electronics within the distributor body. This early AJ6 ignition system is nearly identical to the system used on the XK engine in the Series III XJ6 cars. The Lucas fuel injection system on the AJ6 engines in these early XJ-S cars sensed engine load using a Manifold Absolute Pressure (MAP) sensor just like the V12 cars from the same era. Later AJ6 engines as used in the 1986–1989 XJ40 cars had a crank-sensor type of ignition system with a bare distributor that only carried the spinning ignition rotor inside the distributor cap. The fuel-injection system used on the later AJ6 engines used a hot-wire Mass Air Flow sensor to determine engine load. Vehicles using the 3.6 were: 1984–1989 Jaguar XJ-S 1986–1989 Jaguar XJ6 1986–1989 Jaguar XJ6 Sovereign 1986–1989 Daimler 2.9 The used a SOHC head from the Jaguar V12 engine, and was prone to failure. The block is the same as the 3.6, with the crankshaft and pistons lowering the stroke to . Only the 1986–1989 Jaguar XJ6 used the 2.9.