Mitsubishi 4A91 1.5 MIVEC Engine - Replacement Cost, Problems & CompatibilityProblems & Compatibility

A reconditioned 4A91 supply-only typically costs between £480 and £800, with fitted prices ranging from £850 to £1,200 depending on labour and additional parts. Used units start from £358 supply-only, while full rebuilds run £800-£1,200. Used pricing is [THIRD-PARTY] from Motorinsul UK; reconditioned pricing is estimated. Prices vary by variant - 109 hp units may command a small premium over lower-output variants. Supply-only excludes fitting; add 6-8 hours at £65-£85/hr for specialist installation. Always compare quotes - prices can vary by 20% between specialists.

• Prices vary by variant - 109 hp units may command a small premium over lower-output variants.
• Supply-only excludes fitting; add 6-8 hours at £65-£85/hr for specialist installation.
• Always compare quotes - prices can vary by 20% between specialists.

Oil consumption is the most common issue on the 4A91, typically due to coking of the piston rings or wear of the valve stem seals. Oil consumption can reach 1 litre per 6,000-7,000 km (3,700-4,300 miles) on higher-mileage examples. Timing chain stretch and tensioner wear are also common beyond 80,000-120,000 miles, particularly if oil changes have been neglected. Oil leaks from the front crankshaft oil seal and exhaust manifold-to-catalyst o-ring failure are also documented. Timing chain inspection is recommended at 80,000-120,000 miles. The engine has an estimated lifespan of approximately 140,000 miles (225,000 km). Regular oil changes using 5W-30 or 0W-20 specification oil are critical to longevity.

• Timing chain inspection is recommended at 80,000-120,000 miles.
• The engine has an estimated lifespan of approximately 140,000 miles (225,000 km).
• Regular oil changes using 5W-30 or 0W-20 specification oil are critical to longevity.

The 4A91 is fitted to multiple Mitsubishi models from 2004 to 2015: Mitsubishi Colt Z30 (2004-2013) as the 1.5 MIVEC, Mitsubishi Lancer CY (2008-2017) as the 1.5 MIVEC/Inform, Mitsubishi Mirage Z30 (2004-2012) as the 1.5 MIVEC, and Mitsubishi Lancer Sportback CY0 as the 1.5 MIVEC. It was also used in the Smart Forfour (2004-2006) as a naturally aspirated option. 102-109 hp in UK applications. The engine is part of the 4A9 family and was widely used in Chinese-market vehicles. Check your V5C or engine block stamp to confirm your exact variant.

• 102-109 hp in UK applications.
• The engine is part of the 4A9 family and was widely used in Chinese-market vehicles.
• Check your V5C or engine block stamp to confirm your exact variant.

For most 4A91 owners, a reconditioned unit with new piston rings, valve stem seals and timing chain components is the recommended choice - it addresses the engine's key weaknesses and comes with a 12-24 month warranty. Used units (£358-£480) are very affordable but carry high risk without documented oil change history. Rebuilds (£800-£1,200+) are only justified for low-mileage, high-value examples or sentimental vehicles. Used: only with documented oil change history and timing chain condition. Reconditioned: best balance - all common weak points addressed, warranty included. Rebuilt: ideal for low-mileage, well-maintained examples or long-term keepers.

• Used: only with documented oil change history and timing chain condition.
• Reconditioned: best balance - all common weak points addressed, warranty included.
• Rebuilt: ideal for low-mileage, well-maintained examples or long-term keepers.

The engine code is stamped on a machined pad on the engine block (typically on the front, below the cylinder head) and appears on the V5C under 'Engine number' - the code will read 4A91 followed by additional characters. Use a Mitsubishi VIN decoder to confirm the exact variant from the build sheet. 4A91 (102 hp): 141 Nm torque, lower-output tune (Colt Japan spec). 4A91 (105 hp): 141 Nm torque, mid-output tune (Colt UK/Europe). 4A91 (109 hp): 145 Nm torque, highest tune (Lancer, Lancer Sportback). Fitting the wrong ECU variant will cause drivability issues.

• 4A91 (102 hp): 141 Nm torque, lower-output tune (Colt Japan spec).
• 4A91 (105 hp): 141 Nm torque, mid-output tune (Colt UK/Europe).
• 4A91 (109 hp): 145 Nm torque, highest tune (Lancer, Lancer Sportback).
• Fitting the wrong ECU variant will cause drivability issues.

The 4A91 is a generally reliable engine with an estimated lifespan of approximately 225,000 km (140,000 miles) with proper maintenance. The all-aluminium construction saves weight (approximately 25 kg over cast-iron designs), but the engine requires diligent maintenance - regular oil changes using 5W-30 or 0W-20 specification oil are critical, particularly given the timing chain's dependence on oil quality. Budget for timing chain inspection around 80,000-120,000 miles. Oil consumption should be monitored from around 60,000 miles. The 4A91 is significantly lighter and more fuel-efficient than the older 4G15 it replaced. Regular oil changes and good quality fuel are the best preventative measures.

• Budget for timing chain inspection around 80,000-120,000 miles.
• Oil consumption should be monitored from around 60,000 miles.
• The 4A91 is significantly lighter and more fuel-efficient than the older 4G15 it replaced.
• Regular oil changes and good quality fuel are the best preventative measures.