w245 CDI euro5 won't start

[Exp21]

Watching EPC they are the same

 

[mersum1es]

There is your answer, should be 1600 bar.

are you kidding?...

215bar should be enough.

 

[Exp21]

are you kidding?...

215bar should be enough.

Agree with you. I think that for starting 130 bar are enough. Now I'm trying to access the relays box but it's a real mess

 

[mattkh]

are you kidding?...

215bar should be enough.

No.
If it is a common rail direct injection (CDi) then it is that high a pressure...1600 bar.

 

[mersum1es]

So it is not fuel pressure/pump related.

I would check next if crank and cam sensor are getting sync (though that should trigger a fault).

 

[mersum1es]

No.
If it is a common rail direct injection (CDi) then it is that high a pressure...1600 bar.

LOL

1600 bar is max pressure of the system. I can't remember if I have ever seen 1600 bar even flooring my car (= max fuel injected).

At starting limit is indeed around 150 bar, which is sufficirent to allow injection. At idle pressure is somwhere 200-300 bar.

BTW too high pressure trigger a fault code too, if actual sensor value is much higher than asked pressure.

 

[Exp21]

So it is not fuel pressure/pump related.

I would check next if crank and cam sensor are getting sync (though that should trigger a fault).

Do you exclude the relay of the fuel pump? It starts some times, others not (only cranks)

 

[mersum1es]

well in diesel relay rarely is problem, and in malfunction it won't let pressure rise at all. If there is enough pressure to allow injection (~150 slightly depending which engine you have), its not pump related. Next possible culprit is problems with timing = crank sensor or cam sensor. If sync is confirmed, that also allows injection to start. So next thing is why injection is not happening... I am not familiar with OM640 engine and its fuel system, OM646 engine has a fuel temp sensor which fault may prevent starting. If OM640 has one, see what reading it is giving.

 

[mattkh]

OM646 engine has a fuel temp sensor

Is this sensor for heating the diesel fuel in the winter..?

 

[mersum1es]

Is this sensor for heating the diesel fuel in the winter..?

No, it is a sensor, not a heater!

And there is no such thing as a heater, if there is a heat exchanger in fuel return line, it is actually for cooling purposes.

 

[alexanderfoti]

No.
If it is a common rail direct injection (CDi) then it is that high a pressure...1600 bar.

Only at high rpm, high load. At low rpm or idle its 200-300bar

 

[alexanderfoti]

well in diesel relay rarely is problem, and in malfunction it won't let pressure rise at all. If there is enough pressure to allow injection (~150 slightly depending which engine you have), its not pump related. Next possible culprit is problems with timing = crank sensor or cam sensor. If sync is confirmed, that also allows injection to start. So next thing is why injection is not happening... I am not familiar with OM640 engine and its fuel system, OM646 engine has a fuel temp sensor which fault may prevent starting. If OM640 has one, see what reading it is giving.

Yes +1 check for cam/crank sync during non star, star will show you but a good aftermarket tools should also.

 

[Exp21]

Thank you all really for your answers. I explained not so well the problem. I don't know if during cranking (when it won't start) there's enough pressure to the rail. Because unfortunately when I tried to watch with diagnosis live data, the engine started immediately. Even today it started perfectly many times. My suspect is that when it doesn't start the fuel pump is not activated at all by the faulty relay.

As soon as problem comes back I'll update the post

 

[alexanderfoti]

Thank you all really for your answers. I explained not so well the problem. I don't know if cranking there's enough pressure to the rail. Because unfortunately when I tried to watch with diagnosis live data it started immediately. Even today it started perfectly. My suspect is that when it doesn't start the fuel pump is not activated at all by the faulty relais.

As soon as problem comes back I'll update the post

That really is annoying, we get it all the time!

 

[Exp21]

I'll keep you posted

 

[Exp21]

Is this the crankshaft sensor, right?

Anyway still no trouble codes and now car starts perfectly . I'll have to use it until it won't start again. In this situation I think that not even the dealer could do a correct diagnosis.

Thank you

 

[alexanderfoti]

Yes that is it. Crankshaft sensors usually fail when hot, then work again when they cool down. Often no faults, but when in "failed" state you will have no cam/crank sync.

 

[Exp21]

Thank you for help, really!

In my autel scanner there's a dedicated section for diagnosing "cranks but won't start". But if I start the car I see "Not synchronized" during cranking, and as soon as engine starts it says synchronized. So it's really hard to understand if it's a sync problem, because even when it starts properly, during cranking it says "not sync".

I'll let you know what I find

 

[Exp21]

I noticed a detail. During cranking, rpm tachometer doesn't move. Do you think this could lead the diagnosis to crank/cam sensors? Or in this car is normal that the tachometer doesn't move at all due to a too low cranking speed?

20210505_163208_1.mp4

www.amazon.it

 

[Exp21]

Hi everyone. Today won't start at all .

I made a video of the cranking from Autel diagnosis. It says "synchronized" so I suppose cranking sensor is fine? And I also see enough rail pressure. So I really don't know. If someone could help me I'd be grateful, thank you

cranking.mp4

www.amazon.it

When cranking I see a voltage dropping under 11V. Could this be the cause? Battery has only 2 years, genuine MB by varta