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Mitsubishi 4A90 Specifications
| Engine Model: Mitsubishi 4A90 |
| Engine Type: 4-cycle inline 4-cylinder DOHC 16-valve liquid-cooled gasoline |
| Total Displacement: 81.3 cu.in (1.33 L) |
| Rated Engine Power: 95-105 Hp (70-78 kW) at 6000 rpm |
| Fuel System Type: Sequential multi-point electronic fuel injection |
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| General Technical Data |
The Mitsubishi 4A90 is a 1.3-liter inline four-cylinder gasoline engine developed as part of the 4A9 family co-engineered by Mitsubishi Motors and DaimlerChrysler during the early 2000s. It was introduced in 2004 as a modern lightweight power unit designed for compact vehicles, combining aluminum construction, efficient combustion, and smooth operation.
The 4A90 featured double overhead camshafts
(DOHC) and four valves per cylinder, with a focus on reducing weight,
friction, and emissions while achieving adequate performance and fuel
economy. It replaced earlier Mitsubishi small-displacement engines such
as the 4G13 and 4G15, offering improved refinement and compliance with
Euro 4 and later Euro 5/6 emission standards.
The early standard 4A90 variant employed a fixed-timing DOHC design with
multi-point electronic fuel injection, producing moderate power suitable
for urban and subcompact cars. Later developments included the 4A90
MIVEC version, equipped with Mitsubishi Innovative Valve timing
Electronic Control, allowing variable intake cam phasing for improved
torque, responsiveness, and emissions control.
These updates helped the engine meet stricter
environmental regulations and enhanced drivability. The engine was
widely used in Mitsubishi Colt, Smart Forfour, and several other compact
models, known for its smoothness, low vibration, and long service life
when maintained correctly.
The Mitsubishi 4A90 has a total displacement of 1,332 cc (81.3 cubic
inches), achieved through a bore of 75.0 mm (2.95 inches) and a stroke
of 75.0 mm (2.95 inches), forming a square engine geometry for balanced
performance. The compression ratio is typically 10.5:1 for the standard
version and slightly increased to 10.9:1 in MIVEC-equipped variants. The
engine utilizes an aluminum alloy block with cast-iron cylinder liners
and an aluminum alloy cylinder head.
This configuration ensures strength and thermal
efficiency while minimizing weight. The crankshaft is forged steel,
supported by five main bearings, providing stability at higher engine
speeds. Pistons are lightweight aluminum alloy with molybdenum-coated
skirts to reduce friction. Connecting rods are fracture-split forged
steel for high precision and durability.
The valvetrain layout consists of twin overhead camshafts (DOHC)
operating four valves per cylinder via low-friction roller rocker arms
and hydraulic lash adjusters. Camshafts are driven by a single-row
timing chain with an automatic hydraulic tensioner. The firing order is
1–3–4–2, and the engine rotates clockwise when viewed from the front.
Idle speed is electronically maintained at approximately 750 ± 50 rpm.
Maximum power output for the standard 4A90 is rated around 70 kW (95 Hp, 94 bhp) at 6,000 revolutions per minute, with maximum torque of approximately 125 Nm (92 lb-ft) at 4,000 rpm. In the later MIVEC variant, power increased to 78 kW (106 PS, 105 bhp) at 6,000 rpm, and torque rose to about 133 Nm (98 lb-ft) at 4,250 rpm. The redline is near 6,800 rpm, with ECU-controlled fuel cut around 7,000 rpm.
| Fuel System |
0The 4A90 engine employs a multi-point electronic fuel injection (MPI) system. Fuel is delivered by an electric in-tank pump through a high-pressure line to the fuel rail and solenoid injectors positioned on the intake ports. The fuel pressure regulator maintains constant differential pressure relative to manifold vacuum, around 300 kPa (43 psi).
The engine control unit (ECU) monitors multiple sensors, including
throttle position, mass air flow, intake air temperature, oxygen, and
crankshaft position sensors, to optimize fuel delivery and ignition
timing. The standard version uses a conventional throttle cable, while
later MIVEC and Euro 5/6 variants employ an electronically controlled
throttle (drive-by-wire).
The recommended fuel is unleaded gasoline with an octane rating of 95
RON (approx. 91 AKI). Fuel consumption varies depending on vehicle model
and transmission but generally averages between 5.5 and 6.0 liters per
100 km (43–47 mpg US). The injectors should be inspected and cleaned
every 80,000 km (50,000 miles), and the fuel filter replaced every
40,000 km (25,000 miles). The fuel return line ensures excess fuel is
sent back to the tank, maintaining stable pressure and preventing vapor
lock.
| Lubrication System |
0The lubrication system is a fully pressurized wet-sump design. A
trochoid oil pump driven by the crankshaft supplies oil to the main
gallery, feeding the crankshaft journals, connecting rods, camshafts,
and valve train components. Piston cooling jets are incorporated to
spray oil on the undersides of pistons, reducing temperature and
preventing knock. The oil filter is a spin-on type located on the front
side of the block. Normal oil pressure at 3,000 rpm is approximately 400
kPa (58 psi), while at idle it is around 100 kPa (15 psi).
Oil capacity with filter change is approximately 3.3 liters (3.5 US
quarts, 2.9 Imperial quarts). Recommended oil grade is SAE 0W-20 or
5W-30 meeting API SM or SN standards. Mitsubishi specifies oil change
intervals of 10,000 km (6,000 miles) or six months, whichever comes
first. The positive crankcase ventilation (PCV) system reduces blow-by
gas emissions and maintains clean crankcase operation. Excessive oil
consumption is rare if the engine is serviced regularly and high-quality
oil is used.
| Cooling System |
The 4A90 employs a liquid cooling system with a belt-driven centrifugal water pump and aluminum cross-flow radiator. The thermostat begins to open at approximately 82 C (180°F) and is fully open by 95°C (203°F). The cooling circuit circulates coolant through the block, head, heater core, and radiator to ensure uniform temperature distribution.
The radiator fan is electrically controlled by the ECU, switching on at
about 96°C (205°F) and off at around 90°C (194°F). The cooling system
capacity is approximately 5.5 liters (5.8 US quarts, 4.8 Imperial
quarts). The coolant mixture should be 50% ethylene glycol antifreeze
and 50% distilled water, providing freeze protection to –35°C (–31°F).
The coolant should be replaced every 40,000 km (25,000 miles) or every
two years. The system includes sensors for coolant temperature, which
feed data to both the ECU and the dashboard gauge. Overheating is rare
if the radiator and thermostat are maintained in good condition. Proper
coolant maintenance is essential to prevent corrosion in the aluminum
components.
| Intake and Exhaust Systems |
The intake manifold is made from lightweight composite material to
reduce heat absorption and weight. The intake system is tuned to enhance
mid-range torque and uses a resonator to suppress induction noise. The
air filter element is a dry paper type, replaceable every 20,000 km
(12,000 miles). MIVEC versions utilize an electronically controlled
throttle body for precise airflow regulation.
The exhaust manifold is cast stainless steel and connects to a
close-coupled catalytic converter to ensure rapid light-off during cold
starts. Downstream oxygen sensors monitor catalyst efficiency. Later
MIVEC variants feature secondary air injection during cold starts to
accelerate catalyst heating and lower emissions. The exhaust system
includes a flexible joint to minimize vibration transmission.
| Ignition and Electrical System |
The 4A90 uses a distributor-less ignition system with four individual coil-on-plug units controlled by the ECU. Spark plugs are iridium-tipped for long life, typically NGK IFR6E11 or equivalent, gapped to 1.1 mm (0.043 inch). Replacement interval is 100,000 km (62,000 miles).
The alternator output is rated around 90 amperes, and the 12-volt electrical system uses a 45–55 Ah battery. The starter motor is a compact reduction-gear type rated at approximately 1.0 kilowatt. Ground connections are made through reinforced straps to ensure consistent electrical performance.
| Valve Timing and Drive Mechanism |
Timing is by a roller chain connecting the crankshaft to the camshafts, with an automatic hydraulic tensioner maintaining correct tension. In standard 4A90 engines, valve timing is fixed. The MIVEC versions incorporate a hydraulically actuated intake cam phaser that varies cam timing up to approximately 30 degrees of crankshaft rotation.
This allows optimization of valve overlap for improved torque at low speed and increased efficiency at high speed. The system operates through oil pressure regulated by a solenoid valve controlled by the ECU based on load, rpm, and temperature. Chain replacement is not part of regular maintenance but should be inspected after 150,000 km (93,000 miles) for elongation or tensioner wear.
| Dimensions and Weight |
The overall dimensions of the 4A90 engine assembly are approximately 610 mm (24.0 inches) in length, 630 mm (24.8 inches) in width, and 670 mm (26.4 inches) in height. Dry weight is around 95 kg (209 lbs) for the standard version and approximately 100 kg (220 lbs) for the MIVEC variant due to additional components. The engine’s compact dimensions and light weight contribute to efficient front-end packaging and balanced vehicle dynamics. The engine mounts are rubber-isolated to minimize noise and vibration transmission to the chassis.
| Maintenance Data |
Engine oil and filter replacement are recommended every 10,000 km (6,000 miles). Air filter replacement should occur every 20,000 km (12,000 miles). Spark plug replacement is due at 100,000 km (62,000 miles) for iridium types. Coolant should be replaced every 40,000 km (25,000 miles) or two years. The accessory drive belt should be inspected every 40,000 km (25,000 miles) and replaced at 80,000 km (50,000 miles).
Valve clearance is maintained automatically by hydraulic lash adjusters, eliminating periodic adjustment. The timing chain requires inspection at high mileage but generally lasts the life of the engine. Compression pressure for a healthy engine is approximately 1,400 kPa (203 psi) per cylinder, with a minimum allowable of 1,000 kPa (145 psi). The permissible difference between cylinders should not exceed 100 kPa (15 psi).
| Tightening Torques |
Cylinder head bolts: 30 Nm (22 lb-ft), then 90 degrees, then an
additional 90 degrees.
Main bearing cap bolts: 60 Nm (44 lb-ft).
Connecting rod bolts: 40 Nm (30 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: 25 Nm (18 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).
Engine mount bolts: 60 Nm (44 lb-ft).
Valve cover bolts: 8 Nm (6 lb-ft).
| Vehicle Applications |
The 4A90 engine was widely fitted in compact cars from Mitsubishi and
Smart, reflecting its efficiency and reliability.
Notable applications include:
– Mitsubishi Colt (Z30, 2004–2012)
– Mitsubishi Colt Plus (2005–2013)
– Mitsubishi Mirage (limited markets)
– Smart Forfour (W454, 2004–2006)
– Proton Savvy (with derivative design elements)
– Various export-market compact Mitsubishi models
The engine was produced in several global manufacturing plants,
including Mizushima, Japan, and MDC Power in Germany. Its combination of
low emissions, lightweight construction, and reliable performance made
it popular in both Asian and European markets.
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