Mercedes-Benz M104 engine (1989-98)

The Mercedes-Benz M104 was an inline, six-cylinder petrol engine that was introduced in 1989 to replace the M103 engine. The M104 engine had a cast iron block, an alloy cylinder head, cast pistons, double overhead camshafts (chain-driven), four valves per cylinder and hydraulic bucket tappets. Furthermore, all M104 engines had camshafts adjusters on the intake camshaft. Of these,

• 104.98 engines advanced the camshaft 34 degrees on activation; and,
• 104.99 and 104.94 engines advanced the camshaft 32 degrees.

Production of the M104 engine ended in 1998, having been superseded by the M112 engine.

CIS-E, LH-SFI and HFM-SFI injection systems

Initially, the M104 engine had the electronically-controlled CIS-E (Bosch KE-Jetronic) mechanical injection system. The CIS-E system provided knock control and could advance camshaft timing, while ignition was controlled by a separate EZL (‘Elektronische Zündanlage’) i.e. ignition control module. M104 engines with the CIS-E system also had an exhaust camshaft-driven distributor.

From March 1991 to September 1993, the W140 E 300 and S 320 models with the M104.99 engine had Bosch LH-Jetronic (LH 4.1) sequential fuel injection (SFI). Commonly abbreviated as LH-SFI, these engines had exhaust camshaft-driven distributors and a separate EZL. The M104.99 engines were also distinguished by their aluminium intakes and round port cylinder heads.

From 1993, the M104 engines had fully electronic HFM (Hot Film Mass Airflow Sensor) ignition systems with integrated electronic ignition and sequential fuel injection. These HFM-SFI systems used coils that were mounted directly on the spark plugs, replacing the distributor at the front of the engine. Each coil pack provided spark to two spark plugs simultaneously: one connected directly to one plug and the other with a short high tension lead to the next spark plug. As a result, there were three coil wires and three high tension lead wires. The HFM-SFI system had adaptive technology that could compensate for conditions such as engine wear and u Nmeasured intake air to maintain driveability as the engine aged. Furthermore, the HFM-SFI system could retard spark timing to prevent knocking in affected cylinders, unlike EZL which would retard spark timing for all cylinders.

3.6-litre M104.941 AMG engine

The M104.941 AMG engine powered the W124 E 36 AMG, W202 C 36 AMG and W210 E 36 AMG models. With a 92.4 mm stroke and 91.0 mm bore, the 3606 cc displacement of this engine was achieved by increasing the bore of the 2.8-litre block by 2.1 mm and using a modified crankshaft from the 3.5-litre OM603 engine to increase throw by 18.9 mm. Other changes for the M104.941 AMG engine included:

• Aluminium-forged pistons (with shorter skirts) which were cooled by additional oil jets;
• A finely balanced crankshaft;
• A larger intake crossover pipe;
• A free-flowing exhaust;
• A unique intake camshaft;
• Minor cylinder head changes;
• Modified HFM-SFI engine management system (Motronic M 3.4.2); and,
• Sodium-cooled exhaust valves.