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. For example C250 instead of 230E or 280SE or190E, etc.

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 .

Mercedes-Benz OM605.910 engine

The Mercedes Benz W202 range of Petrol  & Diesel Cars

C180 and the C180T,  
C200 Kompressor, C200 Diesel, C200T Diesel, C200 CDI  
C220, C220T, C220 Diesel, C220 Diesel T,
C230, C230 Kompressor, C230T, C230T Kompressor, 
C240 and the C240T, 
C250D and the C250 Turbodiesel 
C280, C280 (V6) and the C280T (V6) , 
C36 AMG. 
C43 AMG and the C43T AMG 
C55 AMG and the C55T AMG 

However, the only  engine of interest at this point in time is :- Mercedes-Benz C250D 83kw normally aspirated in-line (straight) diesel engine (OM 605.910). Only 44,801  cars with the aforementioned engine were manufactured between 1992-1996. The Mercedes Benz C250D 110kw Turbodiesel  engine (OM 605.960) is essentially the same engine but sports an added turbo charger. Again only 59,772 were manufactured between 1995-2000. These two engines are in fact the little brothers of the Steyr-Daimler-Puch tractor (OM 606.964) 3.0 litre engine which is essentially the four valve per cylinder successor of the OM617 two valve per cylinder engine. An engine proven  to  exceed  500 000 to 1 million miles before needing an overhaul and is therefore considered to be one of the most reliable engines ever produced.

Mercedes-Benz OM605.910 dual overhead cam engine with intake manifold,
valve cover and high pressure injector pipes removed 

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. 

Mercedes-Benz C250D diesel fuel seals

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 your fingerprints off . I've encountered glow plugs with good continuity (1.5 ohms) but when I connected the 12V  across them, using  jumper leads, all I got was a spark on connection and no steam nor heat, it was  dead glow plug even though  it had continuity. Also bear in mind, there are three things needed to start a diesel engine.

1) Compression - The air in the combustion chambers is placed under such enormous pressure that it's hot enough to ignite the diesel spay spontaneously.

2) Diesel - Supplied under pressure (115 bar) must be devoid of air bubbles. Bleed off air before attemtping to start the engine.

3) Electricity (12V) - 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 likelihood when it doesn't start wouldn't be compression  associated. Diesel engine compression range between between 275 psi and 495 psi,  with typical compression ratios of between 15:1 and 23:1. When diesel is sprayed into the combustion chambers through the diesel injector nozzles - the moment the air in the chambers are under great pressure - it's normally hot enough to ignite the diesel spontaneously. However, when compression is suspect, an average pressure of 300 psi is good but no cylinder should vary by more than 10 percent.  Anything greater than 50 psi difference between cylinders will also cause starting problems,  poor acceleration, diesel knock, excessive smoke and can lead to rough idling. 

The part numbers for the 6 hoses are 605 070 12 32, 605 070 10 32,
605 070 15 32, 605 070 07 32, 605 070 08 32, 605 070 14 32,

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.

The part numbers for the 6 hoses are 605 070 12 32, 605 070 10 32,
605 070 15 32, 605 070 07 32, 605 070 08 32, 605 070 14 32,

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.

Clear diesel pipe attached to clogged filter

Fuel filter cleaned out 

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 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.

Shutoff valve with the seals removed

O rings slightly bigger than the ones that were removed.

 The only way I was going to get the end caps back in place was with a clamp.

Shutoff valve closed with "O" ring on nozzle that fits into diesel pump.

MERCEDES BENZ W202 C-CLASS C250D

MERCEDES BENZ W202 C-CLASS 250D 

The Internet without any doubt, is the world's largest data repository of information. It sports information of every kind and virtually topic. Yet, I find it very surprising how little useful information it actually contains. I'm not trying to be facetious, but that is just the reality of the situation - It is what it is. Much of this "information" is however duplicated, often copied from the same sources, regurgitated,  blogged, forumed and re-echoed by millions of websites in virtually every language.

Out of the tens of billions of web sites globally, there is truly very little origination, containing genuine helpful details that unselfishly assists others, expecting nothing in return.  Virtually every website out there is trying to sell you something online. Ranging from services to physical products to vapour ware. Some trying to scam you with things ranging from snake oil to overpriced trinkets. Others entice you to register with their sites  that deliver porn related pop-ups of  naked females and sex toys. There are even some with links and pop-ups that promises great wealth. Not forgetting those that spam you with junk mail, Trojans and viruses that hijack your browser. All of them shouting credit card very loudly.

Electronic fuel pump that leaks.

Be that as it may, when you have automotive trouble and the "automotive technicians" or service agents wants to charge you an arm and a leg to fix it, its time for DIY, especially if you have nibble hands.  However, when you get stumped and need a little assistance, it would really be nice to know that an Internet search would produce credible and helpful information and not fictitious, overused and worthless nonsense. My search on the subject I was interested in, delivered hoards of YouTube videos, flaunting mostly superfluous information. 

Their creators being more interested in potential advertising revenue that can be earned from those overbearing adverts prefixed to their video instead of actually creating content that will really help a fellow car owner. Here, I'm specifically eluding to information on the Mercedes Benz  C-Class 250D Sedan W202 phase-I 1993-1997 which seems to be in extremely short supply. Not even the Mercedes Benz service agent have any form of on-line help worth mentioning, considering the car in question is just about  20 years old.  But allow me to digress for a moment. 

My wife had endless trouble with her 1989 Mercedes Benz 124 230E, to the point that she threw in the towel because she just couldn't battle the constant high cost of repairs any longer. These cost didn't  even include the cost associated with its regular upkeep.

Her troubles started out with her car overheating which turned out to be a leak in the radiator which caused the cylinder head gasket to blow. The temperature warning light only came on when it was already over 120 degrees. Since the car already had more than 350 000 km on the clock we decided on a complete engine and radiator replacement, which came in at quite a cost. Shortly thereafter a leaking steering pump was replaced because she found it impossible to steer when the hydraulic fluid ran low. What a mission, the intake manifold and the steering rack had to be removed to replace it.



 Months later, the starter bendix started to drag and the starter was replaced. Thereafter the complete right front hub was replaced along with the knuckle because of two wheel nuts that broke off in the hub, that just couldn't be removed. Drilling it out and re-tapping the holes invariable was going to cost more than a complete hub, so new hub was fitted. Then the battery gave up the ghost and shortly thereafter the alternator died which were both replaced along with two new tyres.

Somehow after the steering rack replacement, the car just didn't perform well,  even though wheel alignment was done. For some reason the front wheels would shudder when driving over an expansion joint on bridges.  Thereafter the car suffered from intermittent switch off and had difficulty starting. Several weeks later the starter gave up the ghost a second time due to extended cranking. Hardly was the starter replaced when the sound of metal rubbing against metal alerted me to the fact that the brake pads were at end of its useful life. Front and back break pads were replaced, only to find out that the handbrake engaged but didn't stop the car from rolling. So it needed brake shoes as well. Meanwhile the car still switched off when getting to stop signs and had difficulty starting it again.



This turned out to be a stretched timing chain causing the distributor timing to change every so often. The gear driving the distributor  every so often slipped a tooth or two because of the slack in the timing chain . After battling to get the chain tensioner  bolt and spring out and removing a link, the chain was too short and the link was put back.  At this point we just had enough because the car had started to rust. We decided to scrap the 230E and went out to buy a slightly newer Mercedes Benz that we could afford, because it is the only car that my wife ever drove and couldn't drive stick either. Our choice was the Mercedes Benz Elegance 1996 C-Class 250D W202 which was in a relatively nice condition considering she just turn 20. The best part, she was within our budget.

However, within  months we started having problems  with the C250D. The speedometer stopped working yet my wife continued using the car until the mailman delivered a traffic fine for speeding. So I went out a bought an instrument cluster. After replacing it ,  it still didn't work. It looked identical, the plugs were identical, each having the same number of pins. The difference was that the diesel version revved up to 6000 RPM whereas as the gasoline instrument cluster revved up to 7000 RPM. The rev counter behaved like  the speedometer and the fuel guage just climb towards full even though in reality there was less than a quarter tank showing on the original instrument cluster.



Shortly thereafter the the gearbox died which was due to a faulty radiator/oil cooler that allowed water to enter the gearbox through the oil cooler / radiator. Considering the W124 and the W202 use the same gearboxes, we fitted the W124 gearbox after swopping over the tail pieces. 

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Hardly was the gearbox replaced, when the Merc cranked with difficulty in the morning, and she smoked profusely when it eventually idled after several attempts to start her.  Somehow thereafter she would start every time and drove perfectly normal for the rest of the day.  Restated, the first start of the day often ran the battery down.

To Continue.... 
I intend to outline how each of these repairs were affected with pictures to assist those Mercedes Benz  250D W202 owners who are experiencing similar problems with Mercedes Benz C250D W202, 

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Mercedes Benz C250D.