Mitsubishi 4A91 MIVEC Engine Specs

The Mitsubishi 4A91 MIVEC is a 1.5-liter naturally aspirated inline-four petrol engine produced since 2008, used across a range of Mitsubishi's compact models including the Lancer, ASX, and Colt. It represents a mainstream, general-purpose engine in Mitsubishi's lineup, built around simplicity, reasonable efficiency, and affordable ownership rather than outright performance.

Producing 109hp and 143Nm of torque from 1,499cc, the 4A91 uses a DOHC 16-valve aluminum head with Mitsubishi's MIVEC variable valve timing on the intake camshaft, along with a balance shaft system to smooth out the inherent vibration of a small-displacement inline-four running at higher RPM. A compression ratio of 10.5:1 and conventional port fuel injection keep the design mechanically straightforward, and a timing chain drive removes the cost of scheduled belt replacement from the ownership equation.

Reliability has generally been solid across the 4A91's applications, and its mechanical simplicity - no turbocharger, no direct injection - means fewer potential failure points than more advanced modern engines. That said, a handful of items are worth checking on a used example. The balance shaft bearings, which smooth out engine vibration, can wear over very high mileage, sometimes producing a faint rattling or knocking noise that is worth having a mechanic assess if noticed. The MIVEC solenoid, like variable valve timing solenoids generally, depends on clean oil to function correctly, so consistent oil changes with the correct viscosity are important for keeping the variable timing system working as intended. The oil pump and its pickup screen should be part of routine inspection on higher-mileage examples, and the timing chain, while durable, is worth having checked for stretch or noise as the vehicle ages. The PCV (crankcase ventilation) system should also be serviced periodically to prevent oil-related deposits from building up over time. None of these issues are expensive relative to the engine's low purchase and running costs, and the 4A91 remains a sensible, low-risk choice for buyers prioritizing affordable, predictable ownership over performance.