Mercedes-Benz M104 engine

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M104
Overview
Manufacturer Mercedes-Benz AG
Production 1989-99
Combustion chamber
Configuration Straight-6 (Except M104.900, refer VW VR6)
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
Combustion
Fuel system Bosch KE-Jetronic electronically controlled, mechanical fuel injection
Management Electronic
Fuel type Gasoline
Oil system Wet sump
Cooling system Water cooled
Output
Power output 162 kW (217 hp) SAE J 1349 M104.98x
Torque output 265 N·m (195 lb·ft) @ 4600 RPM M104.98x
Chronology
Predecessor M 103
Successor M 112

The Mercedes-Benz M104 was a straight-6 automobile engine produced from 1989 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 chassis.

2.8 L M104.900[edit]

Mercedes needed a compact 6 cylinder for their vans and asked Volkswagen if they could use the VR6 Golf/Jetta engine. An agreement was reached and the engines were sold semi completed to MB. Basically only the engine cover and aircleaner housing is by MB.

3.0 L M104.98x[edit]

This 3.0 L(2996cc) 24v DOHC was introduced as a sports car resp. top model completing the line-up of M103 12V engines. M103 and this engine were replaced by the later 2.8l and 3.2l versions of M104. It was found in the W124 300E-24 models, C124 300CE-24 models, T124 300TE-24 models and R129 300SL-24 models. The 3.0 L M104 produced 217 hp (162 kW) to 231 hp(without catalytic version) and features KE-Jetronic fuel injection, cylinder specific ignition-timing, variable valve timing and under-piston cooling jets. Due to the missing switchable induction pipes low end torque was quite poor.

2.8 L M104.94x[edit]

In 1993, two capacities replaced the 3.0 litre: a 2.8 litre replaced an old single-cam M103 engine and a 3.2 litre replaced a double-cam M104.98X. The 2.8 L M104 produced 193 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 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[edit]

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, Ssangyong Musso and Rexton

AMG 3.4 L[edit]

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 300E AMG 3.4, AMG 3.4 CE and 300TE-3.4 AMG (Mercedes-Benz W124, C124, S124) vehicles, Produced between 1988-1993. Amount of oil in engine is 7.5 litres and amount of coolant in engine is 9 litres. It made 200kW at 6500rpm and used Bosch KE-Jetronic (CIS-E) injection.

AMG 3.6 L M104.941[edit]

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 280 horsepower (210 kW) at 5,750 rpm and 284 pound-feet (385 N·m) of torque at 4,000 rpm using the HFM engine management system. AMG later conceded that since the engine was hand modified, power outputs could vary slightly from 276 hp to 287 hp.

The boost in displacement was obtained by boring the 2.8 litre M104 block by 2.1MM and using a highly modified version of the crankshaft from the 3.5L OM603 to increase throw by 18.9MM; this necessitated the use of new forged pistons with shorter skirts. A larger intake crossover pipe, freer flowing exhaust, a unique intake camshaft, minor changes to the cylinder head, and modifications to the HFM fuel computer also contribute to the increase in power.

AMG 3.6 Liter M104 in a W124 E36T AMG

Turbo Conversions[edit]

Turbocharger kits were offered for both the M103 and M104 engines by Turbo Technics, Mosselman, Lotec, Turbobandit, MAD modify and other tuners. These conversions typically raised engine output to between 300 and 800 horsepower (600 kW)(depend on Boost Target). 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). Today turbocharger kits for M103-M104 engines are available from later tuners in Europe and Asia.