MERCEDES BENZ STARTING PROBLEM

MERCEDES BENZ STARTING PROBLEM

The Mercedes-Benz C-Class 250 TD (W202) sedan and the T-model station wagon with the OM605 5-cylinder engine manufactured from 1992-2000 is probably one of the rearest cars in the Mercedes stable. The W202 model C-Class cars were the first to display the modern Mercedes-Benz naming scheme, where the badged numbers are followed by letters. The W202 shape with the "facelift" replaced the original W201 190 series sedan; "Baby Benz" (1982-1993) though less than 2 million W202 models were produced since its inception. The W202 shape came in a number of engine capacities, with slight difference in their bodies. Below is a list of some of the W202's manufactured between 1992 and 2000 with engines ranging from the 4 cylinders in-line (straight) engines of the C180 to the V8 of the C55T AMG . This extremely successful Mercedes-Benz OM606 3.0 litre engine, is an inline-six cylinder double overhead camshaft (DOHC) diesel engine sporting indirect injection.

Likewise the Mercedes-Benz OM605.910 / OM605.960 is the 2.5 litre inline-five cylinder double overhead camshaft (DOHC) diesel engine also sporting indirect injection. These engines are relatively noisy because of indirect diesel injection yet they are strong and powerful, with low fuel consumption and excellent reliability. Diesel engines have two peculiarities, they are sometimes difficult to start and sometimes difficult to switch off. Both of which are relatively easy to repair. Often times starting difficulty is associated with the glow plugs. Glow plugs are essentially 12V heater elements fitted to the combustion chamber that heats up, to ignite the first sprays of diesel from the injectors. A continuity test between the the engine block (earth) and the glow plug connector node will determine whether any of them are open circuit. Continuity or a low resistance reading (typically between .5 and 4 Ohms) doesn't necessarily mean the glow plug is operational. The best test is to remove the glow plug, dip the heater tip into a bit of water and connect 12V to the glow plug using jumper leads.

Earth/negative terminal to the body of glow plug and Live/Positive to the connector node. The water will turn into steam even before the glow plug tip glows red. That's sufficient to know that the glow plug is functional. Be careful not to touch the tip, it will burn you the fingerprints off . Compression - The air in the combustion chambers is placed under such enormous pressure that it's hot enough to ignite the diesel spay spontaneously. Bleed off air before starting the engine. Needed to power the glow plugs , the electronic shutoff valve and the diesel pump. When engine is hot, glow plugs aren't needed any longer since the engine is fitted with a diesel pre-heater. So if any one of the above three is missing, the car won't start. The assumption is that if the car starts everyday and displays sufficient torque, the likely hood when it doesn't start wouldn't be compression associated.

Another problem with this engine are the clear diesel pipes or rather its seals that leak, allowing air into the fuel line causing the injector pump pressure to drop substantially. When this happens, the battery can often be drained before the engine is cranked long enough to buildup 115 bars of pressure. However, a squirt of Spanjaard Quick Start spray into the intake manifold should get her idling. But, this screams very loudly that there is some sort of problem that needs to be solved sooner than later. So remove intake manifold, check the glow plugs, test them as mentioned above. Next remove the six clear fuel lines and check the "O" rings for leaks and if they are wet with diesel replace them with those supplied by Mercedes-Benz. I've tried various "O" rings from several sources and believe me, they don't work and always leak. The ones from Mercedes-Benz agents are silicon rubber based, manufactured with a tight tolerance.

Next check the shut off valve for leaks. The "O" ring behind the shut off valve tends to perish because it endures the heat transferred from the engine block to the injector pump. Do yourself a favour and get the right one. It will save you time and money. The grime that clogged the fuel line. Also check the hoses clamps on the fuel lines between the non return fuel cut off valve and the fuel heater/exchanger. I had a very minute, hardly visable, crack in my car's heat exchanger. Early Mercedes-Benz W202, were fitted with biodegradable wiring harnesses. Unfortunately, this biodegradable insulation deteriorated much quicker than it was anticipated due to moisture and heat in the engine compartment. I had to replace mine because there was more visible copper than insulation on the wires. So check the harness between the shut off solenoid valve and the ECU for cracks and brittleness; replace if necessary. Also clean the small fuel filter, its bound to have dirt in it. Perished wiring harness and fuel hoses that needs replacement. And lastly, check the shut off valve at its ends for leaks, if it does leak, replace the seals. The seals are held in by four pins that needs to be pushed out in order to get to the seals. Unfortunately Mercedes Benz agents do not supply these seals separately. One has to purchase the complete shutoff valve at the some ridiculous price which I just couldn't justify. The ones I used were roughly 31.88mm in diameter, slightly larger than the ones that came out. Putting them back was an itch with a B. As can be seen I used a G clamp that worked wonderfully indeed.