Ok, so you have a Merc diesel car you trust, but suddenly it will not start?
May have had some increasing problems (longer and longer time to start) unto it no longer starts, or just a suddenly stop on the road - and restart again after a lot of waiting?

I have been there, and I didn't find a tutorial to help me out in search for my error.
Probably because I had two errors at once, both regarding the diesel flow, and I only searched for one error at a time.

So this is a quick post that may be of benefit to you if you ever get problems with stops or starts on you diesel engine.

This post is put together after getting a lot of help from forum members here, and also another foreign language forum. I am very grateful, and want to give back by collecting much information into one post that can benefit many (hopefully).


You can probably use this guide / thought process on most diesel engines,
but since I have most experience with the MB E300 TDT (1998) s210, that will be the "model" for this post.

Word of warning: Do not crank more than appr. 30 seconds. I have cranked as long as 60 seconds, but the start engine may turn too hot and break.


Start and stop problems:
Can be caused by

• leakage in the diesel system
• by a mechanic error in the solenoid in the Shut Off Valve (SOV)
• or by an electronic error.

Symptoms:

#1: If the engine is NOT stopping:
If the engine is not stopping when you turn off the engine, it is most probably the SOV that is defect. The solenoid can be stuck.

The SOV should only be open (car is running) as long as it gets power (12V). The power is cut when the engine is stopped by the key, or the onboard computer turns off the engine due to a "alert". So if the engine is NOT stopping, then the SOV is defect. Solution: get a new SOV.


#2: If the engine is stopping while driving, and you need to wait 10-30 minutes before you can start it again:
It is most probably a detector/ sensor that is defect. I can't remember it's name in English, but one way to test this is to cool it down with a cooling spray (just after an unexpeckted stop) and see it the engine will start sooner than "normal".

I believe this sensor is placed below glow plug #5 on my car, but I am not sure, as I have never had this issue.


#3: If the engine will not start at all:
(This only applies if you can crank, but you get no start. If you can not crank, the error is a different place.) You can crank and crank, but it will not start.

My experience is that it can be 2 causes:

1) The engine can not suck enough diesel from the tank
or
2) The SOV is not activated/ open, and thus the injector pump does not get diesel.


In the case of 2) : SOV is not clicking
The most simple way to test this is to be 2 persons. One inside the car to turn the key, and one outside to hold onto the SOV. Then the person inside turn the key to position #2. (position where glow plugs glow, but before cranking) If the person holding on the SOV can feel a "click", then the SOV works.

If the SOV is NOT clicking, then either the SOV or the electronics is bad.

You can remove the SOV and put 12 V directly to two pins on the SOV. (there are 4 pins on mine, I can't remember what pins I put 12 V on). 2 pins are for ground + 12V plus. The other 2 pins is for a thermometer for the fuel temp.

Solution: IF the SOV is NOT opening when adding 12V to it directly, then it needs replacement.

IF the SOV is indeed opening, then you can mount it back (Tips: replace the o-ring while you have it up).


So, if the SOV is not defect, there can be some error sources:
a) defect K40-reley (google this)
b) defect cable (from K40 to the SOV)
c) an error code in the brain's memory that tells the brain not to start the engine

You need to read the engines error codes (STAR diagnosis) to get to know if the error source is c)

Check the K40-reley. Check it for burned solder. Check the print card visually. Also slap it carefully just to give the relays a little help to move. Replace it (of fix it) if it is burned.

If the K40 works, and there is no error code in the memory, it is most likely a defect power plug or cable. (On my car it is a bad connection between the cable and the plug that sits on the SOv itself. )


In the case of 1) . SOV is indeed working well , but no start
Ok, if the SOV is indeed working well (you can feel the "click" when turning the key), then the error is most likely a problem with the fuel system.

The error can come from:
1) Old and dirty diesel fuel filter (pre-filter and main filter)
2) A leakage in the o-rings (on each end of each fuel line)
3) A leakage in the fuel lines (you will NOT see diesel leaking out, since there is vacuum inside the lines)
4) Dirt in the tank that plugs the outlet for the fuel


Most probably there is a o-ring that leaks.
My second guess is that one of the transparent fuel lines around the diesel filter is leaking.
My third guess that the black fuel lines (tour / detour) that connects to the fuel pipes are leaking in one of the ends (they kind of turn rotten).

Be careful with the transparent fuel lines. Especially if they are more like orange. Then they are old, and getting hard and are easier to crack when you move them.

This is what I would do:

1) Check the diesel filters
Check the pre-filter to see if it has dirt stuck. Clean it with diesel.
Check the main diesel filter. If you are living a place where the temperature goes below 0' C, then replace it.

So:
If dirty : replace it.
If in doubt: replace it!
If you live in an area that has freezing winters: replace it EVERY fall.

2) Get yourself an overview of what fuel line goes where, and then check them
Then remove one and one, and look at the o-ring. The o-ring should be round (not pressed flat to be flat sided), and should not have any marks. O-rings are cheap, so replace all if you can.

3) If you see that a fuel line is cracked, replace it.
IF you have bad time, and a little money extra, replace all fuel lines. They will someday break, and you'd better change all.


Refill the diesel system
Now your diesel system is empty of diesel, and full of air. You may start to crank and crank the engine, but it will take TIME - and it will drain your battery (and may be kill it).

Yet as easy as this is, it took me quite some time to find this way of doing it...

I suggest this:
Pre-fill both diesel filters to the brim. (You should do this always).

Take an air compressor, a cloth or big paper towel, and detach the detour fuel line from the fuel pipe. Then put a 1/2 litre soda bottle or similar to catch diesel from the fuel line.

You need to be two persons:
One to "fill" the diesel tank with high pressure air (you need to use a cloth or a paper towel as a seal around the compressor gun, so the air is not leaking out there). This will force diesel to flow through the whole system, and get rid of the air.

The person by the engine needs to put his/ hers thumb to seal the fuel pipe that goes to the tank (to make sure air is not going out there), and should see diesel flow through the transparent lines together with air bubbles. The diesel will force most of the air out. This will go to the detour black fuel line, and all diesel spill will be caught in the bottle.

When there is only diesel coming out of the black diesel line, then keep on pumping in air in the diesel tank.

The person in the engine room then put the fuel line back onto the fuel pipe, and mount it back.

Then you can stop blowing in the diesel tank, and the system will be filled with diesel. If you just stops keeping the pressure in the tank before mounting the fuel line back, then the diesel will return to the tank, and suck air into the fuel lines again...


THEN glow the glow plugs and crank the engine. 30 seconds crank, 1 minute wait, 30 seconds crank etc. Stop when the engine revs up and it works.


OK, I hope this is helpful for you.

If you know what the sensor is called (that I mentioned), please name it.

Also please share your thoughts and helpful ideas here :-)


Thank you,
Preben

Good info thank you.

__________________
Diesel effcient