Mercedes-Benz M104 engine

M104

Manufacturer	Mercedes-Benz AG
Production	1990-1999
Predecessor	M103
Successor	M112
Configuration	Straight-6
Displacement	2.8 litres (171 cu in) M104.94x 3.0 litres (183 cu in) M104.98x 3.2 litres (195 cu in) M104.99x 3.6 litres (220 cu in) M104.941
Cylinder bore	88.50 mm (3.484 in) M104.98x
Piston stroke	80.20 mm (3.157 in) M104.98x
Cylinder block alloy	Cast iron
Valvetrain	DOHC, 4 valves per cylinder
Compression ratio	10:1
Fuel system	Bosch KE-Jetronic electronically controlled, mechanical fuel injection
Management	Electronic
Fuel type	Gasoline
Oil system	Wet sump
Cooling system	Water cooled
Power output	162 kW (217 hp) SAE J 1349 M104.98x
Torque output	265 N·m (195 ft·lb) @ 4600 RPM M104.98x

The Mercedes-Benz M104 was a straight-6 automobile engine produced from 1990 through 1999. It was a double overhead cam design with 4 valves per cylinder. It replaced the M103 and was replaced by the M112 V6 starting in 1997. The M104 continued in production until 1999 where its last use by Mercedes - Benz was in the W140 chasis, it was later manufactuered under license by SsangYong Motor Company of Korea.

3.0 L M104.98x

This 3.0 L 24v DOHC engine replaced the 12v 3.0 L M103 engine. It was found in the W124 300E-24 models, W124 300CE-24 models, W124 300TE-24 models and R129 300SL-24 models. The 3.0 L M104 produced 217 hp (162 kW) and features KE-Jetronic fuel injection, cylinder specific ignition-timing, variable valve timing and under-piston cooling jets. It was replaced by the 2.8 L and 3.2 L M104 engines.

2.8 L M104.94x

After the W124 received a facelift, two capacities replaced the 3.0 litre: a 2.8 litre lower-power version and a 3.2 litre version. The 2.8 L M104 produced 194 hp (145 kW) at 5500 rpm. Max torque was 270 N·m or 199 ft/lbs at 3750 rpm. Lubrication system is pressure circulation lubrication. Amount of oil in engine was 7.5 litres (which was later revised to 7 litres) and amount of coolant in engine is 9 litres. The 2.8 features dual overhead camshafts and four valves per cylinder. The camshaft is driven by duplex roller chain. The electrical starter motor produces 1.7 kW. Ignition system is ignition mapping control. The 2.8 L M104 was also used in the W202 C-Class model C280 and in the W140 S-Class model S280 (the latter was not sold in North America).

Whilst the M104 is known to be a reliable engine, there were some technical issues with smooth running. The wiring loom which passed from the Idle Speed Control unit (an electronic box situated in the engine bay) to the ignition coils (housed on the top of the engine) was enclosed under plastic covers. High temperatures were experienced in this region. In addition the plastic insulation was a type which bio degrades with time and heat.

The ignition coils provided current for two spark plugs each. A system of “Wasted spark” was used where one coil powers two spark plugs. But the coils were still subjected to a high heat zone.

Idle speed problems could be experienced if the coils / wiring breakdown damaged the Idle speed controller. This manifested itself with engine not idleing at the correct rpm, normally 667, but hunting could be experienced with the engine ranging up to 1200 rpm. If the coils become damaged they may still operate at low engine rpm normally, but at higher engine loads the coils can break down resulting in engine power loss as the number of power producing cylinders reduce from six to four or even in worse case scenarios two.

Wiring loom upgrade kits were made available with upgraded insulation to resist the heat.

Another problem area is the viscous coupling on the fan. This can degrade over time, resulting in slippage and reduced airflow through the radiator. Higher cooling water temperatures will result, which can overheat the radiator and cause thermal cracking of the radiator headers. (This is considered more of a wear-and-tear issue, which occur with most older cars.)

3.2 L M104.99x

The 3.2 L (3199 cc) version produced 220 hp (161 kW) at 5500 rpm and 310 N·m (229 ft·lbf) at 3750 rpm. This engine was found in the W124 and W210 E-Class, W140 S-Class, W463 G-Class, R129 SL-Class, and Ssangyong Musso.

AMG 3.4 L

There were 3.4 L conversions done to the 3.0 L M104.980 by AMG, prior to their formal cooperation with Daimler Benz.

AMG developed a 3.4 L M104 that was used in the E34 and E34T AMG (W124) vehicles. Amount of oil in engine is 7.5 litres and amount of coolant in engine is 9 litres. It made 272ps at 6500rpm and used Bosch KE-Jetronic (CIS-E) injection.

AMG 3.6 L M104.941

There were 3.6 L conversions done to both the M103 and M104 by Brabus, among others.

AMG developed a 3.6 L M104 that was used in the W202 C36 AMG (W202), the W124 E36 AMG (W124) and the E36 AMG (W210) vehicles.

The AMG 3.6 M104 was rated at 276 horsepower (206 kW) at 5,750 rpm and 284 foot-pounds force (385 N·m) of torque at 4,000 rpm using the HFM engine management system.

The boost in power was obtained by stroking the 2.8 litre M104 using the crank from the 350sd engine.

AMG 3.6 Liter M104 in a W124 E36T AMG

Turbo Conversions

Turbocharger kits were offered for both the M103 and M104 engines by Turbo Technics, Mosselman, Lotec and other tuners. These conversions typically raised engine output to between 300 and 400 horsepower (300 kW). During the 1990s UK customers were able to buy new vehicles equipped with a Turbo Technics conversion directly from Mercedes dealer Hughes of Beaconsfield (limited run of 75 conversions).