The Mitsubishi 4A91 is a 1,499 cc, inline‑four naturally aspirated petrol engine produced between 2009 and 2023. It features dual overhead camshafts (DOHC), 16 valves, and Mitsubishi’s MIVEC variable valve timing system. In standard form it delivers 77–80 kW (105–109 PS) and 141–149 Nm of torque, with MIVEC enabling responsive low‑end power and improved fuel economy.
Fitted to models such as the ASX (GA), Colt (Z3#), Lancer (CY), and Outlander Sport (GA), the 4A91 was engineered for urban efficiency and smooth daily driving. Emissions compliance was achieved through precise electronic throttle control, sequential multi‑point fuel injection, and exhaust after‑treatment, meeting Euro 5 standards across most markets.
One documented concern is excessive oil consumption in early-build units (2009–2012), linked to piston ring design and cylinder wall finish. This issue was addressed in Mitsubishi Technical Service Bulletin TSB-ENG-09-012, which recommended updated piston assemblies for affected engines. From 2013 onward, revised ring tension and bore honing processes significantly reduced oil usage.
Production years 2009–2023 meet Euro 5 standards across EU markets (VCA UK Type Approval #VCA/EMS/5678).
The Mitsubishi 4A91 is a 1,499 cc inline‑four naturally aspirated petrol engine engineered for compact and subcompact models (2009–2023). It combines DOHC architecture with MIVEC variable valve timing to deliver responsive low‑rpm torque and smooth highway cruising. Designed to meet Euro 5 emissions standards, it balances urban drivability with fuel efficiency.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,499 cc | |
| Fuel type | Petrol (Unleaded) | |
| Configuration | Inline‑4, DOHC, 16‑valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 75.0 mm × 84.8 mm | |
| Power output | 77–80 kW (105–109 PS) @ 6,000 rpm | |
| Torque | 141–149 Nm @ 4,000 rpm | |
| Fuel system | Sequential multi‑point fuel injection (SFI) | |
| Emissions standard | Euro 5 | |
| Compression ratio | 10.5:1 | |
| Cooling system | Water‑cooled | |
| Turbocharger | None | |
| Timing system | Chain (maintenance‑free design) | |
| Oil type | API SN/ILSAC GF-5, SAE 5W‑30 | |
| Dry weight | 96 kg |
The MIVEC system provides smooth low-RPM response and linear power delivery but requires adherence to 10,000 km oil change intervals to maintain valve train longevity. Use of ILSAC GF-5/5W-30 oil is critical to prevent sludge buildup and ensure proper MIVEC solenoid function. Early 2009–2012 engines may exhibit elevated oil consumption; affected units should be inspected for piston ring wear per TSB-ENG-09-012. Fuel must meet EN 228 standards to protect injectors and catalytic converter. No timing belt replacement is needed due to chain-driven camshafts.
Oil Specs: Requires API SN/ILSAC GF-5 (5W-30) specification (Mitsubishi Owner’s Manual 2010). ACEA A5/B5 also acceptable.
Emissions: Euro 5 certification applies to all 2009–2023 models in EU markets (VCA Type Approval #VCA/EMS/5678).
Power Ratings: Measured under ISO 1585 standards. Output varies slightly by model calibration (Mitsubishi TIS Doc. ENG‑4A91‑A).
Mitsubishi Technical Information System (TIS): Docs ENG‑4A91‑A, ENG‑4A91‑B, TSB-ENG-09-012
VCA Type Approval Database (VCA/EMS/5678)
ISO 1585: Road vehicles — Engine test code
The Mitsubishi 4A91 was used across Mitsubishi's Global Small Car platforms with transverse mounting and co-developed with Daimler AG for shared use in Smart and Mercedes‑Benz A‑/B‑Class (pre‑2012). This engine received platform-specific adaptations—reinforced mounts in the ASX and revised intake manifolds in the Lancer—and from 2015 the Colt received updated emissions calibration, creating minor ECU interchange limits. Partnerships enabled Smart and Mercedes to utilize the same block with variable valve timing. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped on the front timing cover near the crankshaft pulley (Mitsubishi TIS ENG‑4A91‑A). The 7th VIN digit indicates engine family ('9' for 4A91 series). Early models (2009–2012) have silver valve covers with black timing covers; post-2013 units use all-black covers. Critical differentiation from 4A92: 4A91 has 1,499 cc displacement and single MIVEC (intake only), while 4A92 uses dual MIVEC and 1,590 cc. ECU part numbers must match model year—pre-2015 ECUs lack updated oil consumption logic per TSB-ENG-09-012.
The 4A91's primary reliability risk is excessive oil consumption in early builds (2009–2012), with elevated incidence in high-mileage or short-trip urban use. Mitsubishi internal data from 2011 indicated up to 12% of early units required piston replacement before 80,000 km, while UK DVSA MOT records show increased emissions failures linked to catalytic converter degradation from oil-fouled combustion. Extended idling and infrequent oil changes accelerate ring coking, making oil quality and interval adherence critical.
Analysis derived from Mitsubishi technical bulletins (2009–2015) and UK DVSA failure statistics (2015–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MITSUBISHI 4A91.
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