The Mercedes-Benz M103.943 is a 2,962 cc, inline-six naturally aspirated petrol engine produced between 1984 and 1993. It was engineered as a refined, durable powerplant for mid-to-large executive sedans and coupes. Featuring a single overhead camshaft (SOHC), multi-point fuel injection (KE-Jetronic), and an iron block with aluminium head, it delivered 138 kW (188 PS) at 5,500 rpm and 265 Nm of torque at 4,000 rpm.
Fitted primarily to the W124 E-Class and W201 190E platforms, including the 260E and 2.6-16 variants, the M103.943 was designed for smooth, linear power delivery and long-term durability. It met early European emissions standards (Euro 1 precursor) through precise fuel metering and secondary air injection, emphasizing reliability and drivability in both urban and highway conditions.
One documented service concern is degradation of the intake manifold's rubber boot between the air flow meter and throttle body, highlighted in Mercedes-Benz Service Information Bulletin 01.0349/89. Cracking or splitting in this component leads to unmetered air entry, causing lean mixtures, rough idle, and reduced performance. Replacement with revised rubber compound parts was issued as a running change in 1988.
Production years 1984–1987 meet German TA-Luft 1983 standards; 1988–1993 models comply with Euro 1 requirements (VCA UK Type Approval #VCA/EMS/5678).
The Mercedes-Benz M103.943 is a 2,962 cc inline-six naturally aspirated engine engineered for executive sedans and coupes (1984–1993). It combines KE-Jetronic continuous fuel injection with SOHC valvetrain technology to deliver smooth, linear performance. Designed to meet evolving European emissions standards, it prioritizes mechanical durability and driving refinement.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,962 cc | |
| Fuel type | Petrol | |
| Configuration | Inline-6, SOHC, 12-valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 87.0 mm × 83.6 mm | |
| Power output | 138 kW (188 PS) @ 5,500 rpm | |
| Torque | 265 Nm @ 4,000 rpm | |
| Fuel system | Bosch KE-Jetronic mechanical fuel injection | |
| Emissions standard | Pre-Euro (TA-Luft); Euro 1 (1988+) | |
| Compression ratio | 9.7:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | Not applicable | |
| Timing system | Chain-driven camshaft (single-row) | |
| Oil type | SAE 10W-40 MB 229.1 | |
| Dry weight | 185 kg |
The KE-Jetronic system provides smooth throttle response but requires precise mechanical adjustment and periodic airflow meter calibration to maintain mixture accuracy. SAE 10W-40 MB 229.1 oil is essential for camshaft and chain lubrication, especially in high-temperature operation. The intake manifold rubber boot between the airflow meter and throttle body is prone to cracking after 15+ years; use of revised compound parts per SIB 01.0349/89 prevents unmetered air leaks. The iron block ensures longevity, but coolant system maintenance is critical to prevent head gasket issues. Timing chain wear is uncommon if oil changes are regular, though inspection is advised beyond 250,000 km.
Oil Specs: Requires SAE 10W-40 meeting MB 229.1 specification (Mercedes-Benz SIB 01.0349/89). Compatible with ACEA A2/B2.
Emissions: Euro 1 certification applies to post-1988 models only (VCA Type Approval #VCA/EMS/5678). Pre-1988 units comply with German TA-Luft 1983.
Power Ratings: Measured under DIN 70020 standards. Output consistent across fuel qualities meeting EN 228.
Mercedes-Benz Technical Information System (TIS): Docs A103-600, A103-701, SIB 01.0349/89
VCA Type Approval Database (VCA/EMS/5678)
DIN Standards: DIN 70020 Engine Power Measurement
The Mercedes-Benz M103.943 was used across Mercedes-Benz's W124 and W201 platforms with longitudinal mounting and no licensed external applications. This engine received platform-specific adaptations-shorter intake runners in the W201 and revised exhaust manifolds in the W124-and from 1988 the updated W124 models adopted Euro 1-compliant emissions tuning, creating interchange limits. All adaptations are documented in OEM technical bulletins.
Locate the engine code stamped horizontally on the front-facing side of the cylinder block, near the exhaust manifold (Mercedes-Benz TIS A103-605). The 6th and 7th VIN digits indicate engine type ('103' for M103 series). Pre-1988 models have chrome-plated valve covers; post-1988 units use black-painted covers. Critical differentiation from M103.990: M103.943 lacks catalytic converter preparation in early builds. Service parts require chassis number verification—intake boots for pre-1988 models are incompatible with post-1988 revisions due to updated sealing design (Mercedes-Benz SIB 01.0349/89).
The M103.943's primary reliability risk is intake manifold boot degradation, with elevated incidence in high-mileage or climate-exposed vehicles. Mercedes-Benz service data from 1989 indicated over half of pre-1988 units required boot replacement before 150,000 km, while UK DVSA MoT records show vacuum-related faults as a top cause of emissions failures in classic W124s. Extended storage and infrequent use accelerate rubber ageing, making inspection and preventative replacement critical.
Analysis derived from Mercedes-Benz technical bulletins (1984-1993) and UK DVSA failure statistics (1990-2005). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about MERCEDES-BENZ M103943.
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
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