Daimler engineers were the first to create a diesel engine with four valves per cylinder. This was the inline 6-cylinder OM606, introduced in 1993. It was followed by the debut of 4- and 5-cylinder engines. All of these engines were the last Mercedes pre-chamber diesels, with production of the fours ending in 1998, and the fives and sixes in 2001.
The blocks of these engines are cast iron, with cylinder liners. The drive of the timing and the fuel injector is carried out by one double-row chain.
The younger 4-cylinder OM604 was available only in atmospheric versions with a capacity of 2.0 and 2.2 liters, with power from 74 to 94 hp. For fuel injection on the “fours” was responsible rotary single plunger pump Lucas EPIC of distributive type with electronic control. This pump is capricious and demanding to fuel.
“Five” and ‘six’ were equipped with Bosch in-line fuel injectors with mechanical (only on W124) or electronic control. There were both atmospheric and turbocharged versions. The 5-cylinder OM605 developed from 111 to 148 hp. 6-cylinder OM606 produced from 134 to 174 hp.
Mercedes-Benz 3.0 TD OM606 engine options
| Engine variant | Car model | Power | Torque | Power system | Environmental class |
|---|---|---|---|---|---|
| OM606.910 | W124 E 300 Diesel (non-turbocharged) | 136 hp | 210 Nm | Mechanical fuel injection Bosch | Euro 2 |
| OM606.912 | W210 E 300 Diesel (non-turbocharged) | 136 hp | 210 Nm | Mechanical fuel injection Bosch | Euro 2 |
| OM606.962 | W124 E 300 Turbo Diesel, W210 E 300 Turbo Diesel | 177 hp | 330 Nm | Turbocharged, Bosch VE 44 | Euro 2 |
| OM606.964 | G-Class (G 300 TD) | 177 hp | 330 Nm | Turbocharged, Bosch VE 44 | Euro 2 |
Main characteristics of the OM606 engine
| Characteristics | Value |
|---|---|
| Exact volume | 2996 cm³ |
| Configuration | R6 (inline 6-cylinder) |
| Cylinder block | Cast iron |
| Cylinder head | Aluminum, 24 valves (DOHC) |
| Fuel system | Mechanical injection Bosch |
| Hydrocompensators | Yes |
| Transmission timing | Chain |
| Turbocharging | Yes (for OM606.962, OM606.964) |
| Recommended oil | 10W-40 |
| Fuel type | Diesel |
| Ecological class | Euro 2 |
| Engine life | About 500,000 km |
- Versions OM606.910 and OM606.912 are atmospheric engines, without turbocharger, installed in W124 and W210 cars.
- Versions OM606.962 and OM606.964 are turbodiesels, installed in W124, W210 and G-Class cars.
- The OM606 engine is known for its reliability and durability, thanks to its rugged construction and lack of complex electronics.
Resistance and reliability of older Mercedes diesels
Mercedes diesels are very reliable mechanically. They do indeed easily last a million kilometers or more. If, of course, they receive more or less quality service, not bad oil and not the dirtiest diesel fuel.
Although it is considered that Mercedes diesel engines with 4 valves per cylinder (specifically, OM604, OM605 and OM606) are more capricious than their predecessors.
This diesel still interests tuners, because it is relatively easy to remove from 300 to 500 hp. It is enough to tinker with the turbine (install a high-performance one) and with injection pressure.
Air intake
Criticism deserves fuel lines, which on these motors have switched to quick-release connections, semi-plastic tubes and hoses, flanged fittings and clip-latches. They are not durable, they wear out, crack – as a result, in the under-hood space in some places, there is a dribble of fuel and there are air intakes. Experts say that these particular engines without air bubbles do not exist anymore. But even with air bubbles in the fuel pipes, the OM606 engine starts confidently, but it starts, but it is moving and twitching when working. To combat air sucking, it is desirable to change all the tubes and sealing rings. They are now and the original cost inexpensive.
The dulling of the engine
The OM606 (OM605) engine with a turbine can dull, lose traction or go into emergency mode because of problems with vacuum and vacuum valves (it has two of them, on the turbine and on the EGR valve; number A0005450427).
The problem could also be a faulty boost pressure sensor or even clogged filter-moisture separators (A0000780956) on the EGR valve lines.
Fuel filter housing
On the fuel filter housing, the fuel tubes are connected through rubber rings. Over time, the rings lose elasticity and begin to leak air. In this case, during the night idle time, the fuel simply runs away into the tank, and the system is bled. Starting the engine becomes more difficult, because after turning the key in the ignition switch it takes time to pump the fuel.
Tensioner roller rocker
Inexperienced craftsmen often tear off the thread in the timing cover for the mounting bolt when replacing the tensioner pulley of the timing belt. As a result, the timing cover has to be replaced or something has to be invented to screw the bolt in.
EGR
OM604-OM606 engines are equipped with an exhaust gas recirculation system. It’s fairly simple and usually doesn’t cause any trouble. On the atmospheric engines in this family, it has worked for decades without problems.
On turbocharged versions, the EGR valve is equipped with a position sensor (B28/3). The sensor can fail due to destruction of contact tracks, and the engine will go into emergency mode. The diagnostics will show an error indicating an EGR valve position error.
The EGR valve itself is vacuum controlled by an electromagnetic pneumatic valve, also known as a “transducer” or pressure transducer. Accordingly, EGR problems and related engine behavior problems occur when vacuum leaks or the valve malfunctions.
To disable an EGR with an electronic sensor for its position, the ECU must be re-flashed and re-soldered. If EGR without feedback, it will be enough to install a cheat in the wiring harness, install a plug in the path of recirculated gases and muffle the vacuum tube.
Turbo
The turbocharged OM606 engine is fitted with a BorgWarner K14 turbocharger. No controlled geometry, just a bypass valve. The turbine is a very reliable, durable turbine. It can even survive operation on rather mediocre oil.
The fuel injection system
Fuel supply and injection is provided by Bosch in-line fuel injectors. The atmospheric engine OM606, which debuted and was installed on Mercedes W124, has no control electronics, i.e. the engine has no “brains” at all. On other Mercedes, the OM606 engine already comes with “brains”, the TNVD is essentially the same, but with electronic control, and electronic gas pedal. By the way, the engine with ECU can be installed on an older Mercedes (for example, the motor from W210 to W124) and make it work without any problems. You just need to put in a mechanically controlled fuel injector. The mounts on the pumps and blocks are exactly the same. Even turbocharged OM605 or OM606 will work perfectly normally when converted to mechanical fuel injectors, but a small “tweaking” of the fuel supply will be required.
Fuel injectors are reliable and unpretentious, they are designed to work on low-quality fuel and easily last half a million kilometers. The wear of the fuel injector can usually be heard by a clearly audible noise at speeds up to 1500 rpm without load on the engine.
There are also cases of misadjustment of the fuel injector itself, which usually causes the fuel supply to increase and the injectors to start knocking. This knocking goes away when the nozzle connections are loosened, when part of the fuel is simply blown outward.
Oil and fuel leaks on the fuel injector
The Bosch inline fuel injector is simple and reliable. It has one plunger-piston for the injector of each cylinder. The plungers pressurize and deliver fuel in the required amount. Even after half a million kilometers, this fuel injector works properly, there is no wear.
What happens more often is the leakage of fuel and oil through the rubber seals and rings, which are located under the covers, in the fuel line connections.
All these seals are commercially available, are inexpensive and are changed quite easily.
Fuel injectors
The injectors of OM604-OM606 (and also OM601-OM603) engines are extremely simple. They are essentially a housing with a spring-loaded needle inside. The needle is lifted, opening the atomizer, by fuel pressure. The injectors need to be adjusted to open at the correct pressure. The correct opening pressure is about 135 bar.
The adjustment is made by a spacer between the spring and the needle: the thickness of the spacer affects the opening of the nozzle depending on the fuel pressure.
Due to their simple design and low diesel pressure, the injectors last almost forever and are very inexpensive to repair. When worn, they knock when the engine is cold.
Forcams
The injectors inject fuel into pre-chambers (pre-chambers, not to be confused with vortex chambers) located in the cylinder head. This is also where the glow plugs go (into the prechambers). First, the fuel-air mixture is ignited here, the pressure in the chamber builds up and pushes gases and unburned fuel into the combustion chamber. There they mix with air and burn completely. As a result, the pre-chamber diesel burns fuel in two stages. The combustion itself does not occur instantaneously, but over a period of time. All this is necessary for the sake of smooth pressure increase in the combustion chamber and noise reduction.
The chambers are placed in the cylinder head without any gaskets, and are pressed by special nuts from above. Nozzles are screwed into them and are seated on copper refractory washers.
There are some troubles with the prechambers: gases can burst from under them. But usually it happens because of a hydrostroke, when water gets into the intake or if the injector pours too much fuel.
Also due to a pouring injector or too early injection in the pre-chamber, the splitter – a small partition that stands in the way of the injected fuel – can collapse and fall off. A fragment of the splitter will then rattle in the prechamber when the engine is running. The prechamber will have to be removed (and before that the glow plugs must be removed) and replaced. To remove it, you need a special slotted wrench, which is used to unscrew the nut of the forkamera.
High glow plugs
Glow plugs play a major role in the successful starting of a pre-chamber diesel. They are glowing within a few minutes of starting the engine – until the antifreeze in the area around the cylinder-head has warmed up to 20°C.
If at least one glow plug fails, the pre-chamber diesel will let you know immediately with hesitant starting and ignition skips.
Replacing glow plugs on an OM606 engine is not an easy task. Firstly, the plugs of 2-, 3- and 6-th cylinders are difficult to access (pipelines from the fuel injector and oil filter housing are in the way). Secondly, plugs are broken at a force of more than 45 Nm. That is, if the plugs are even slightly prikoril, they will definitely break in half. Then they will have to be drilled out. Today this operation is carried out without removing the cylinder-head.
The timing chain
The double timing chain from the crankshaft drives the fuel injector and the exhaust camshaft. And the exhaust camshaft drives the intake camshaft by means of a gear drive. It is believed that the timing chain on OM604-OM606 engines tends to stretch. However, there are not many cases of its replacement, and it is changed without special difficulties. It can pass about 500 000 km. Significant stretching of the chain on this engine is an increase in its length by at least 3 mm. In this case, the chain will rattle, and there will be deviations in the fuel injection parameters.
Chain stretching can be checked by the marks on the crankshaft and camshaft: they must coincide with a difference of no more than 3°.
It is not difficult to change the chain, but it is advisable to change the guides and even the sprockets together with it.