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Mitsubishi 3A90 Specifications
| Engine Model: Mitsubishi 3A90 |
| Engine Type: 4-cycle inline 3-cylinder DOHC 12-valve liquid-cooled gasoline |
| Total Displacement: 60.9 cu.in (0.99 L) |
| Rated Engine Power: 70 Hp (52 kW) at 6000 rpm |
| Fuel System Type: Sequential multi-point electronic fuel injection |
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| General Technical Data |
The Mitsubishi 3A90 is a 1.0-liter inline three-cylinder gasoline engine developed as part of the 3A9 engine family by Mitsubishi Motors. Introduced in 2012 for the Mirage (Space Star) compact car series, it was engineered to deliver exceptional fuel efficiency, compactness, and low emissions, while maintaining adequate power for urban and suburban driving.
The engine belongs to Mitsubishi’s modern
lightweight aluminum engine generation, replacing older iron-block
small-displacement units such as the 3G8 series. It was designed with a
focus on friction reduction, thermal efficiency, and low NVH
characteristics, aligning with Mitsubishi’s “Global Small” vehicle
program. The 3A90 has since been produced in several emission-compliant
configurations, including Euro 5 and later Euro 6 variants.
The early Euro 5 version debuted in markets such as Japan and Southeast
Asia, meeting emissions and fuel economy standards through conventional
multipoint fuel injection and simple exhaust aftertreatment. The later
Euro 6 iteration incorporated improved combustion chamber design,
revised cam profiles, optimized piston ring coatings, and an upgraded
catalyst system.
The later models also benefited from
recalibrated engine management software and enhanced exhaust gas
recirculation to meet stricter European emission norms without
compromising drivability. Both versions share a common core design,
emphasizing low weight, serviceability, and reliability. Despite its
small displacement, the 3A90 exhibits smooth operation due to an
integrated balance shaft system and a lightweight rotating assembly.
The Mitsubishi 3A90 engine has a total displacement of 999 cc (60.96
cubic inches), achieved by a bore of 75.0 mm (2.95 inches) and a stroke
of 75.4 mm (2.96 inches). The configuration is inline-three, with dual
overhead camshafts operating four valves per cylinder for a total of
twelve valves. The cylinder block and head are both made from aluminum
alloy to minimize mass.
Cast-iron cylinder liners are integrated into
the block to provide wear resistance. The crankshaft is made of forged
steel, supported by four main bearings, and is paired with light
connecting rods and aluminum pistons designed for reduced reciprocating
mass.
Compression ratio varies slightly between versions: the Euro 5 engine
operates at approximately 11.0:1, while the Euro 6 variant is slightly
higher at 11.5:1 due to optimized combustion efficiency and knock
control strategies. Maximum power output for the standard configuration
is rated at approximately 52 kW (71 PS, 70 horsepower) at 6000
revolutions per minute. Maximum torque is about 88 Nm (65 lb-ft) at 5000
rpm.
The Euro 6 version produces similar peak
figures but with a broader torque curve thanks to improved ECU mapping
and enhanced intake efficiency. The firing order is 1–2–3, and the
crankshaft rotates clockwise when viewed from the flywheel end. Idle
speed is controlled electronically and typically maintained at 750 ± 50
rpm.
The engine employs a chain-driven valvetrain for maintenance-free
operation. A single-row roller chain connects the crankshaft to the dual
overhead camshafts, with a hydraulic tensioner maintaining proper chain
slack. The camshafts operate via roller finger followers and hydraulic
lash adjusters to eliminate manual valve clearance adjustments.
Valve diameters are approximately 31 mm (1.22 inches) for intake and 25 mm (0.98 inches) for exhaust. The pent-roof combustion chamber shape promotes efficient air-fuel mixing and combustion stability. The redline is around 6500 rpm, with fuel cutoff occurring near 6800 rpm.
| Fuel System |
The Mitsubishi 3A90 uses an electronically controlled sequential multipoint fuel injection system. Fuel is supplied by an electric in-tank pump delivering fuel at approximately 350 kPa (51 psi) to the fuel rail. Three solenoid-operated injectors spray atomized fuel directly onto the intake ports.
The ECU regulates fuel delivery based on inputs from the throttle
position sensor, manifold absolute pressure sensor, oxygen sensor, and
coolant temperature sensor. The throttle body is electronically actuated
(ETC), allowing fine control of idle speed and transient response. The
fuel pressure regulator maintains consistent pressure differential
relative to manifold vacuum.
The system operates with unleaded gasoline rated at 95 RON (91 AKI
minimum). In markets where available, the engine can operate on E10 fuel
without modification. Fuel economy in the Mirage with the 3A90 engine
can exceed 4.5 liters per 100 km (approximately 52 mpg US) under
standard driving conditions.
Later Euro 6 versions incorporate an improved evaporative emission control system (EVAP) and lower-permeation fuel hoses to minimize hydrocarbon losses. The fuel filter is integrated into the tank module and designed for the life of the vehicle.
| Lubrication System |
The lubrication system is a fully pressurized wet-sump type driven by a trochoid oil pump mounted in the timing cover and driven by the crankshaft. Oil is drawn through a pickup strainer and delivered through the oil filter to the main galleries feeding the crankshaft bearings, connecting rods, camshafts, and valve train components.
The oil filter is a spin-on type with an internal bypass valve. Normal
oil pressure is approximately 300 kPa (43 psi) at 3000 rpm, dropping to
around 100 kPa (15 psi) at idle. Piston cooling oil jets are used to
spray the undersides of the pistons for temperature control and
detonation resistance.
Total oil capacity, including the filter, is approximately 3.0 liters
(3.2 US quarts, 2.6 Imperial quarts). Recommended oil viscosity is SAE
0W-20 or 5W-30 meeting API SN or higher and ILSAC GF-5 standards. The
Euro 6 version benefits from reduced friction coatings on cam lobes and
piston rings, necessitating high-quality synthetic oil.
Oil change interval is typically 15,000 km (9,000 miles) or 12 months, whichever occurs first. Under severe conditions such as frequent short trips or dusty environments, the interval should be halved. The crankcase ventilation system includes a PCV valve integrated into the rocker cover.
| Cooling System |
The 3A90 uses a liquid-cooled pressurized system with a belt-driven
centrifugal water pump circulating coolant through the block, head,
radiator, and heater core. The thermostat begins to open at 82 C (180
degF) and is fully open at approximately 95 degC (203 degF). Coolant
temperature is monitored by sensors that provide feedback to the ECU and
dashboard gauge. The system operates at a pressure of about 88 kPa (13
psi). Total coolant capacity is approximately 4.2 liters (4.4 US quarts,
3.7 Imperial quarts).
A lightweight aluminum cross-flow radiator and electric cooling fan
maintain stable operating temperature. Later Euro 6 versions introduced
a more efficient coolant flow path and a low-drag water pump design to
reduce parasitic losses. Recommended coolant is a 50/50 mix of ethylene
glycol-based antifreeze and demineralized water, offering freeze
protection to –35 degC (–31 degF). Coolant replacement interval is every
160,000 km (100,000 miles) or 5 years.
| Intake, Exhaust, and Emission Control Systems |
The intake manifold is molded from composite plastic to reduce weight and improve thermal insulation. Long, narrow runners promote strong low- and mid-range torque. The air cleaner uses a replaceable paper-element filter, typically replaced every 30,000 km (18,000 miles). The throttle body is electronically controlled and positioned close to the intake manifold to minimize airflow lag.
The exhaust manifold is integrated into the cylinder head, allowing the
catalytic converter to be positioned near the exhaust ports for rapid
light-off. The system includes an upstream oxygen sensor for closed-loop
fuel control and a downstream sensor for catalytic efficiency
monitoring.
The Euro 5 version uses a conventional three-way catalytic converter
with a secondary air injection system for cold-start emission reduction.
The Euro 6 model features a higher cell-density close-coupled catalyst,
improved O2 sensor response, and enhanced exhaust gas recirculation
(EGR) to reduce nitrogen oxide emissions.
The evaporative emission system (EVAP) includes an activated charcoal canister and purge control solenoid. Combined, these systems enable compliance with global emission standards while maintaining low fuel consumption and drivability.
| Ignition and Electrical System |
The ignition system is fully electronic, utilizing coil-on-plug ignition modules controlled by the ECU. Each cylinder has an individual ignition coil mounted directly above the spark plug, ensuring precise spark timing and eliminating high-tension leads. Spark plugs are iridium-tipped for longevity and efficient combustion.
The standard specification is NGK DILFR6A11 or equivalent, with a gap of 1.1 mm (0.043 inches). Replacement interval is 100,000 km (62,000 miles). The alternator provides approximately 85 amperes of charging capacity, while the starter motor is rated at 1.0 kilowatt. The electrical system operates on 12 volts DC, and the ECU features OBD-II diagnostic capability.
| Valve Timing and Drive Mechanism |
The timing system uses a single-row roller chain for camshaft drive. The Euro 5 engine has fixed valve timing, while the later Euro 6 variant introduced Mitsubishi’s MIVEC (Mitsubishi Innovative Valve timing Electronic Control) system on the intake camshaft. This allows continuous variation of valve phasing for optimized torque, emissions, and fuel economy.
The MIVEC mechanism uses oil pressure to hydraulically advance or retard cam timing based on engine load and speed. This system broadens torque delivery and enhances fuel efficiency, particularly at low and mid rpm.
| Dimensions and Weight |
The overall dimensions of the Mitsubishi 3A90 engine are compact, with a length of approximately 580 mm (22.8 inches), width of 600 mm (23.6 inches), and height of 700 mm (27.6 inches). Dry weight is approximately 69 kg (152 lbs) for the Euro 5 version and about 72 kg (159 lbs) for the Euro 6 version due to additional emission hardware. The lightweight design contributes significantly to the Mirage’s overall fuel efficiency and balanced handling.
| Maintenance Data |
Recommended service intervals include:
– Engine oil and filter: every 15,000 km (9,000 miles) or 12 months.
– Air filter element: every 30,000 km (18,000 miles).
– Spark plugs: inspect at 60,000 km (37,000 miles), replace at 100,000
km (62,000 miles).
– Coolant: replace every 160,000 km (100,000 miles) or 5 years.
– Drive belt: inspect at 40,000 km (25,000 miles), replace at 100,000 km
(62,000 miles).
– Fuel system inspection: every 80,000 km (50,000 miles).
Compression pressure (standard) is approximately 1,400 kPa (203 psi) per
cylinder with a minimum acceptable limit of 1,100 kPa (160 psi). Maximum
variation between cylinders should not exceed 100 kPa (15 psi). Idle
speed is electronically maintained at 750 ± 50 rpm. The ECU stores fault
codes accessible through standard OBD-II scan tools.
| Tightening Torques |
Cylinder head bolts: 25 Nm (18 lb-ft) plus 90 degrees, then an
additional 90 degrees.
Main bearing cap bolts: 55 Nm (41 lb-ft).
Connecting rod bolts: 30 Nm (22 lb-ft) plus 90 degrees.
Camshaft bearing cap bolts: 10 Nm (7 lb-ft).
Crankshaft pulley bolt: 180 Nm (133 lb-ft).
Flywheel bolts: 85 Nm (63 lb-ft).
Spark plugs: 18 Nm (13 lb-ft).
Oil drain plug: 40 Nm (30 lb-ft).
Intake manifold bolts: 25 Nm (18 lb-ft).
Exhaust manifold nuts: 35 Nm (26 lb-ft).
Valve cover bolts: 8 Nm (6 lb-ft).
Engine mount bolts: 60 Nm (44 lb-ft).
| Vehicle Applications |
The Mitsubishi 3A90 engine has been widely used in small passenger
vehicles where light weight, fuel efficiency, and low emissions are
prioritized.
Principal applications include:
– Mitsubishi Mirage (Global model, 2012–present)
– Mitsubishi Space Star (Europe)
– Mitsubishi Attrage / Mirage G4 (sedan variant)
– Smart Forfour (in certain collaborations with Daimler)
The Euro 5 version was primarily installed in early Mirage and Space
Star models sold in Asia and emerging markets, while the Euro 6 variant
powers vehicles in Europe and Japan from 2016 onward. In some markets,
this engine was also tuned for hybrid and start-stop configurations,
further enhancing economy. The 3A90’s compact size, durability, and low
maintenance requirements have made it a cornerstone of Mitsubishi’s
small-car lineup, with over a million units produced worldwide.
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