Mercedes 2.2 CDI OM646 Engine Specs, Problems, Reliability

The 2.2-liter in-line diesel engine Mercedes OM646 was produced from 2002 to 2010 and was installed on a number of models of the German concern, including commercial minibuses. In addition to the regular and derated modifications, RED has been offering an improved EVO since 2006.

The engine was equipped with a Common Rail 2 fuel system. Such an injection is capable of delivering 1600 bar. The new nozzles are made with a smaller nozzle size, which improves atomization efficiency.

Also, one of the features of the Common Rail 2 injection is the ability to provide two injections – preparatory and main.

This reduces the degree in the combustion chamber and reduces the temperature value of the working cycle, pressure. Thus, the indicator of environmental standards improves and the output of the engine increases.

Read Also: Mercedes 2.2 CDI (OM611) Engine Specs, Problems, Reliability

2.2 CDI OM646 Engine Specs

Fuel typeDiesel
Cylinder arrangementIn a row
Number of cylindersFour
Number of valves16
Working volume2.2 l
Maximum power, hp at rpm150 / 4200 (170 / 3000 for turbo version)
Maximum torque, Nm at rpm340 / 2000 (400 / 2800 for turbo version)
Maximum crankshaft speed4000 rpm
Cylinder diameter88 mm
Stroke88.3 mm
Gas distribution system4 valves per cylinder
Compression ratio18.0:1
Characteristics of diesel fuelGOST 305-82
Supply systemDirect fuel injection
Engine locationEngine compartment

The Mercedes 2.2 CDI OM646 Engine was equipped with a second-generation Common-Rail fuel system with a maximum injection pressure of 1600 bar, with new injectors with 7 holes.

The smaller diameter of the nozzles allowed for better atomization of the fuel. The fuel system provided 2 pilot injections.

Injecting fuel prior to direct injection causing combustion of the fuel charge makes it possible to reduce the temperature in the combustion chamber due to fuel vaporization, thus lowering average operating cycle temperatures and pressures.

Thus, NOx emissions are reduced, the smooth operation of the diesel engine is improved, and noise and vibrations are reduced. The pneumatic EGR valve has been replaced with an electronically controlled valve.

In 2006, Mercedes-Benz upgraded the OM646 diesel. The updated OM646 EVO has 90 parts replaced. The diesel compression ratio was lowered from 18.0 to 17.5. Higher pistons and short connecting rods were used.

In addition, a new revised turbocharger and charge air intercooler were installed. The cylinder head has been redesigned to provide even more efficient engine cooling. To improve engine starting, ceramic glow plugs began to be used.

Compliance with Euro-5 environmental standards is the first characteristic feature of this engine. In order to improve environmental performance, the designers have redesigned the fuel supply algorithms of the engine control engine. Other changes have also been made:

  • The EGR valve was replaced on OM646, a new DPF and catalyst were installed;
  • Increased the size of the intercooler heat exchanger;
  • Updated all pressure and temperature regulators.

Modifications:

  • OM 646 DE 22 LA RED or 200 CDI
  • OM 646 DE 22 LA or 220 CDI
  • OM 646 DE 22 LA EVO RED or 200 CDI
  • OM 646 DE 22 LA EVO or 220 CDI
AspiratedTurbo version
Engine volume, cc21482148
Maximum torque, N * m (kg * m) at rpm.340 (35) / 2000400 (41) / 2800
Fuel usedDiesel fuelDiesel fuel
Fuel consumption, l/100 km6.84.8 – 8.9
Engine’s typeIn-line, 4-cylinder, direct injectionIn-line, 4-cylinder, direct injection
Number of valves per cylinderfourfour
Maximum power, hp (kW) at rpm150 (110) / 4200170 (125) / 3000
Add. engine informationDOHCDOHC
CO2 emissions, g/km127 – 237127 – 237
Cylinder diameter, mm8888
Compression ratio16.2 – 18.116.2 – 18.1
Piston stroke, mm88.388.3

2.2 CDI OM646 faults and how to fix them

  1. Frequent problems of the Mercedes 2.2 CDI OM646 Engine are badass. 2 and 3 connecting rods are deformed, liners wear out. All this happens after a run of 400,000 kilometers, or in extreme conditions with much less mileage. Wiping on the liner leads to knocking, stopping idling.
  2. The solution is to replace the crankshaft, liners. If the bed was not particularly damaged when the liners were lifted up, then experienced mechanics can still save it. The repair will be difficult and will cost money. Check crankshaft bearings for alignment.
  3. Therefore, Common Rail equipment becomes a problem. It most often crashes in the vehicle. The system is capricious. Loves high-quality and clean fuel. Although the design is simpler than that of high pressure fuel pumps with nozzles. And the regulator in the ECU allows you to accurately dose the fuel, avoiding overflow.
  4. Bearing wear leads to oil leakage into the cold or hot part. This problem cannot be determined in garage conditions. Since a special stand is required. Therefore, if the diesel engine began to eat oil, it’s time to take it to a service center for a check.
  5. Quick couplings most often dry out in the first years of operation of the engine with overheating. The system is aired. The engine starts to sneeze, stalls. Experienced mechanics recommend replacing the fitting.
  6. Alternator pulley failure is accompanied by noise. If you miss this moment, you can get wear on the belt tensioner. Solved by installing a new pulley.
  7. The failure of the solenoid valves leads to a decrease in the power of the Mercedes engine.
  8. Stretching the timing chain is a favorite problem of the 2.2 CDI OM646 Engine . Solved by replacing the chain with a new one. Also, the cylinder head camshaft drive often wears out.
  9. Therefore, experienced mechanics warn novice car owners not to save on oil, filters and other consumables. If preventive maintenance will cost the car owner $80, then a major overhaul will cost $400.

By contacting the service center in time, it is possible to identify the problem at an early stage. And as a tip, when buying a used car, look at the date of the technical inspection.

Conclusion

Despite the fact that the engine from the Mercedes 2.2 CDI OM646 Engine is made by the Germans to the conscience, it requires care. Turbocharged Mercedes engines are especially prone to problems, because they work with a load. Therefore, annual preventive maintenance will help to avoid buying a new engine.

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