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 en…
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 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.
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.
The most common questions about engine codes, what they mean, how to find them and how this database works
The 4A91 is generally reliable, especially post-2013 models with updated pistons. Early units (2009–2012) had oil consumption issues, but with regular oil changes (every 10,000 km) and correct 5W-30 oil, most engines exceed 200,000 km without major issues.
Top issues include excessive oil consumption (early builds), MIVEC solenoid faults due to sludge, plastic thermostat housing leaks, and intake runner sticking. All are documented in Mitsubishi TSBs and can be mitigated with proper maintenance.
The 4A91 appears in the ASX (2010–2023), Lancer (2009–2017), Colt (2009–2012), and Outlander Sport. It was also used by Smart (Fortwo 1.0 MHD) and Mercedes-Benz (A150) under co-development agreements from 2009–2014.
Modest gains are possible. ECU remaps typically yield +5–8 kW, limited by naturally aspirated design. Forced induction is rare and requires extensive modification. Most owners focus on drivability improvements rather than significant power increases.
Excellent for its class. In an ASX 1.5, expect ~7.2 L/100km (city) and ~5.1 L/100km (highway), or about 48 mpg UK combined. Real-world mixed driving typically returns 45–52 mpg (UK) with conservative driving.
Yes. The 4A91 is an interference engine. If the timing chain were to fail (extremely rare), piston-to-valve contact would cause severe internal damage. However, the chain is designed to last the engine’s lifetime with proper oil maintenance.
Mitsubishi specifies SAE 5W-30 oil meeting API SN/ILSAC GF-5 (or ACEA A5/B5). Always use a quality synthetic blend and change every 10,000 km to protect MIVEC components and prevent sludge-related issues.
Comprehensive technical documentation and regulatory references
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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