w245 CDI euro5 won't start

[Exp21]

Good morning, I really need your help because my w245 B200 CDI won't start some times. Engine cranks but won't start. It started with this issue yesterday, and today starts once every 5 attempts I would say. The only fault code I have is a 169100 error due to the B16/14 exhaust gas temperature sensor, a story that goes on from 2 years. So I don't think this could be the cause. I replaced the sensor weeks ago, and error code is still there. I'm trying to determine the cause with some people from France and here in the forum but nobody (included mechanics can determine the issue).

When it starts, engine goes well, as always. No engine light, no trouble codes (at least with my Autel scanner). Does anyone know how to proceed for a step by step diagnosis? The fact that starts only some times makes me exclude a burn fuse.

If I detach the inlet diesel hose that goes from tank to diesel filter I can measure the flux of diesel in litres/min. Is it a good way?

Thank you so much for help

 

[robin.large]

I'm not the expert but in general my experience of pumps is that they work, don't work very well, or don't work at all.
Because you say that when started all is good then I'm thinking it probably isn't the pump.
It may be that the fuel pressure is bleeding away when stopped? Injector bleeding down? Pressure regulator? Fuel Pump seals?

Sent from my ONEPLUS A5010 using Tapatalk

 

[mattkh]

Good morning, I really need your help because my w245 B200 CDI won't start some times.
Thank you so much for help

Engine code..?
Mileage.?

 

[Exp21]

Thanks for your answer. If it's a leaking or rail issue, shouldn't I have trouble codes?

@mattkh OM640 (the exact part after the . I don't remember I have to check), mileage is low, 90k miles. And head gasket already replaced

 

[mattkh]

Thanks very much.
Why was the head gasket replaced..?
Sorry, a Pass on the leak question.

 

[Exp21]

It had a small oil leak externally. So many jobs have been done on this car that if I told you, you wouldn't believe me

 

[mattkh]

It had a small oil leak externally. So many jobs have been done on this car that if I told you, you wouldn't believe me

In that case, the line of action normally is whatever was the last thing done to the car is the first suspect.
By the way, has the tensioner for the timing belt been changed..?

 

[Exp21]

yes, chain and tensioner kit. The thing that seems absurd is the absence of error codes. I have to proceed like any "won't start" diagnosis. Step by step I suppose

 

[mattkh]

yes, chain and tensioner kit. The thing that seems absurd is the abscence of error codes. I have to proceed like any "won't start" diagnosis. Step by step I suppose

Generally, with diesels not firing, one thinks of air bubbles in the fuel..
Have the O rings in the fuel lines been replaced..?

 

[mersum1es]

Low fuel pressure at cranking won't trigger a code. Try read live data and see what is rail pressure.

 

[Exp21]

During cranking I think it was 215 bar, I tried before.

About o-rings I don't know. All jobs have been done at MB dealers. The only job that did an indy was replacing the hp pump with a used one (certified).

 

[mattkh]

During cranking I think it was 215 bar, I tried before.

There is your answer, should be 1600 bar.

 

[Exp21]

Years ago a MB technician told me that w169 and w245 cdi models suffered from low pressure diesel pump issues. Honestly I have the suspect that it's the responsible for that. It goes once, and then not for 3-4 times. The ultimate proof could be hammering it under the tank when it doesn't start. I know it often works.

The fuel flux should be about 2L/min. If I detach the fuel hose going to the diesel filter I can watch how much diesel comes right away. What do you think?

 

[mattkh]

Years ago a MB technician told me that w169 and w245 cdi models suffered from low pressure diesel pump issues. Honestly I have the suspect that it's the responsible for that. It goes once, and then not for 3-4 times. The ultimate proof could be hammering it under the tank when it doesn't start. I know it often works.

The fuel flux should be about 2L/min. If I detach the fuel hose going to the diesel filter I can watch how much diesel comes right away. What do you think?

Risky, because you may be introducing air bubbles.
I would also look into the O rings for the fuel lines.

 

[Exp21]

Risky, because you may be introducing air bubbles.
I would also look into the O rings for the fuel lines.

If I only detach the hose and turn ignition on I shouldn't damage anything I think . I only see if diesel arrives at the filter. Then when I put the hose back on the filter I purge air turning ignition on 2-3 times for 30 seconds and it should be fine. I also found that many times the relay gives problems.

And also a cable near the low pressure pump that oxidizes. It won't be easy

 

[mattkh]

I also found that many times the relay gives problems.

Which relay is this..?
I would definitely rule this out first.

 

[Exp21]

I just checked, the relay is the K100K (A0009828023), you find it under the glovebox (at least for mine with lefthanddrive). If you need you find it on youtube.
Minutes ago car started perfectly, many times. And I could hear clearly the relay "clic" after 10 seconds I turned ignition on, when the fuel pump stops working. Now I have to wait until the problem shows again to see if it's the relay.

 

[mattkh]

I just checked, the relay is the K100K (A0009828023),

Thanks.
That is the Fuel Pump relay.
Just pull it out. Use a very very fine sand paper to clean all the pins, and push it back in firmly.
Take a picture of the relay pins before and after.

 

[Exp21]

I think I'll try to swap the relay with the rear window heater one, they should be identical. If it starts I'll know it's the relay. And if the heater won't work at the same time with the suspect relay, it'll be even clearer the diagnosis.

 

[mattkh]

I think I'll try to swap the relay with the rear window heater one, they should be identical. If it starts I'll know it's the relay. And if the heater won't work at the same time with the suspect relay, it'll be even clearer the diagnosis.

Good idea BUT I will be surprised if they are the same.