320CDI long cranking and difficult start

[salihdeniz]

Dear Members,
This is Salih from TURKEY.
Mercedes 2007 R320CDI(W251) 210000km.
After the car stays a night; I try to start in the morning; the engine cranks but it does not start at the first time.
Second start; the engine starts like it's brand new.
During the day; no problem and so much fun to drive.

What we tried till now;
- Bosch diagnosis programme ==> No fault
- Injectors leakage test ==> 2 of 6 injectors replaced and introduced
- 6 glow plugs ==> replaced (eve no sign or errors dtedted)
- Crank angle sensor ==> replaced
- Rail sensor ==> replaced
- High pressure fuel pump sensor ==> replaced
- High pressure pump ==> replaced
- battery ==> replaced
- cranking speed measured and compared with another CDI320 ==> perfect
- fuel filter ==> replaced
- no leakage observed

We' ve been working on the car for a month but our minds stopped!
All comments are highly appreciated.
Do you recommend to replace the low pressure pump in the fuel tank or to insert a check-valve on the line that is from the low pressure tank to the fuel filter?
Thanks in advance.
Salih DENİZ

 

[Naraic]

Check the transparent fuel lines for air bubbles. If they are present change the o rings and the pipes.

 

[salihdeniz]

Check the transparent fuel lines for air bubbles. If they are present change the o rings and the pipes.

Dear Naraic,
Thanks for your suggestion.
Where are the transparent fuel lines.(all black rubber in our car)
Thanks again.
Salih

 

[alexanderfoti]

Don't think you will have transparent fuel lines on the v6 cdi.

Sounds like you have an issue with the fusible link in your glow plug relay/control module

 

[alexanderfoti]

Don't think you will have transparent fuel lines on the v6 cdi.

Sounds like you have an issue with the fusible link in your glow plug relay/control module

Replacing it should sort it.

 

[salihdeniz]

Don't think you will have transparent fuel lines on the v6 cdi.

Sounds like you have an issue with the fusible link in your glow plug relay/control module

Thank you AlexanderFoti,
We are focusing on glow plug control module as well.
Only the question is, no error message on the screen or Bosch diagnosis programme?
Tomorrow We' re gonna replace the control unit with another ML320CDI which we do not have doubt of its performance.
HAve you faced the same situation and managed to solve with the glow plug control module?
Thanks again.
Salih

 

[alexanderfoti]

Thank you AlexanderFoti,
We are focusing on glow plug control module as well.
Only the question is, no error message on the screen or Bosch diagnosis programme?
Tomorrow We' re gonna replace the control unit with another ML320CDI which we do not have doubt of its performance.
HAve you faced the same situation and managed to solve with the glow plug control module?
Thanks again.
Salih

Yes it's quite common for the output of the glow break to break. They have a small fusible link inside them that breaks. Normally when the plugs short out.

They will often not log fault codes when broken in this scenario.

Good plan to swap controller, just make sure they are the same part number.

 

[salihdeniz]

Yes it's quite common for the output of the glow break to break. They have a small fusible link inside them that breaks. Normally when the plugs short out.

They will often not log fault codes when broken in this scenario.

Good plan to swap controller, just make sure they are the same part number.

Thank you Alexander,
We' ll check the part numbers and swap the control units; and surely let you know about the result.
Have shiny week.
Salih

 

[Steve@Avantgarde]

If the glow plug relay fails, it will log a fault code that it’s inoperable and the glow light will stay on the dash.

The things you need to establish are:

At ignition position 2 do you have 280-300bar of fuel pressure at the fuel rail? On crank do you have more than 160bar?

If yes, all of the fuel system is operative, the fault is injectors somewhere?

If no, there must be poor delivery or air in the lines getting in somewhere. The rubber hoses from the tank lines to the engine usually split on these.

 

[alexanderfoti]

D

If the glow plug relay fails, it will log a fault code that it’s inoperable and the glow light will stay on the dash.

The things you need to establish are:

At ignition position 2 do you have 280-300bar of fuel pressure at the fuel rail? On crank do you have more than 160bar?

If yes, all of the fuel system is operative, the fault is injectors somewhere?

If no, there must be poor delivery or air in the lines getting in somewhere. The rubber hoses from the tank lines to the engine usually split on these.

do these not fail silently when the fusible links melt?

 

[Steve@Avantgarde]

D
do these not fail silently when the fusible links melt?

No. Always leave a fault code.

 

[alexanderfoti]

Aha in that case, sorry for the wrong info OP

 

[salihdeniz]

If the glow plug relay fails, it will log a fault code that it’s inoperable and the glow light will stay on the dash.

The things you need to establish are:

At ignition position 2 do you have 280-300bar of fuel pressure at the fuel rail? On crank do you have more than 160bar?

If yes, all of the fuel system is operative, the fault is injectors somewhere?

If no, there must be poor delivery or air in the lines getting in somewhere. The rubber hoses from the tank lines to the engine usually split on these.

Thank you very much for your detailed explanation Steve.
There is no fault code on the dash. or Bosch diagmostic programme.
You mean the the rubber hoses from the fuel tank to the fuel filter?
We have observed the low pressure pump which is in the fuel tank; if there is anything wrong at its suction port.
It's all clean and working; during this operation we did not see any leakage on the pipes.
Since it is reaaly difficult to reach those hoses which are under the right back seat; today we are going to swap the glow plug control unit from another ML320CDI and try. (a hope)

If it does not work; as an idea; we think that there is a check valve mechanism inside the low pressure fuel pump that is in the fuel tank.
If that check valve is leaking back, the fuel hoses can not stay full of fuel as the car stays over the night.
do you recommend to put a check valve somewhere before the fuel filter so that the fuel will be ready as we first start cranking?
Thanks again for your suggestions.
Have a shiny week.
Salih

 

[salihdeniz]

Aha in that case, sorry for the wrong info OP

Dear Alexander,
Either case we' re gonna swap the glow plug control units; as a hope.
I could not understand the rubber hoses that Steve@Avantgarde advised us to change.
Are those the hoses from the fuel tank and all the way under the car to the fuel filter?
We thought that if there is air intake on those hoses, ther should also be a leakage out?
It is better to ask Steve.
Thank you very much again for your advices.
Kind regards.
Salih

 

[salihdeniz]

Thank you very much for your detailed explanation Steve.
There is no fault code on the dash. or Bosch diagmostic programme.
You mean the the rubber hoses from the fuel tank to the fuel filter?
We have observed the low pressure pump which is in the fuel tank; if there is anything wrong at its suction port.
It's all clean and working; during this operation we did not see any leakage on the pipes.
Since it is reaaly difficult to reach those hoses which are under the right back seat; today we are going to swap the glow plug control unit from another ML320CDI and try. (a hope)

If it does not work; as an idea; we think that there is a check valve mechanism inside the low pressure fuel pump that is in the fuel tank.
If that check valve is leaking back, the fuel hoses can not stay full of fuel as the car stays over the night.
do you recommend to put a check valve somewhere before the fuel filter so that the fuel will be ready as we first start cranking?
Thanks again for your suggestions.
Have a shiny week.
Salih

Dear Steve,
One quick question; did you mean the rubber hoses from the fuel tank to the fuel filter?(all the way under the car?)
second question is about the check valve issue which I mentioned on my previous post?
Thanks in advance for your response.
Salih

 

[Steve@Avantgarde]

Hi Salih

The hoses I mentioned are the rubber ones from the metal tank lines to the metal lines on the engine. They are connected by 2 rubber pipes and commonly leak.

You are going to technical too quickly looking at check valves etc. Although that is a possibility (one I have never come across though) establish the basics. Which is fuel pressure. A CDI engine just needs 2 fundamentals to start, compression and it requires the correct fuel pressure. If you have the basic answers to my questions above you can move on to the next step. You need to see if it has good crank pressure (above 160bar) and stable rail pressure 280-300bar on ignition pos 2.

From memory the tank pump is an electric fuel pump that should prime at ignition and hold between 3.8-4.2bar. That should be easy to test. All you would need to do is connect a fuel pressure tester in line after the pump on the fuel supply side and turn the ignition on. The gauge won't lie! It will then confirm or absolve the tank pumps from blame.

Have you also coded the quantity correction values into the ECU from the replacement injectors?

You may need STAR diagnosis to help you proceed.

 

[salihdeniz]

Hi Salih

The hoses I mentioned are the rubber ones from the metal tank lines to the metal lines on the engine. They are connected by 2 rubber pipes and commonly leak.

You are going to technical too quickly looking at check valves etc. Although that is a possibility (one I have never come across though) establish the basics. Which is fuel pressure. A CDI engine just needs 2 fundamentals to start, compression and it requires the correct fuel pressure. If you have the basic answers to my questions above you can move on to the next step. You need to see if it has good crank pressure (above 160bar) and stable rail pressure 280-300bar on ignition pos 2.

From memory the tank pump is an electric fuel pump that should prime at ignition and hold between 3.8-4.2bar. That should be easy to test. All you would need to do is connect a fuel pressure tester in line after the pump on the fuel supply side and turn the ignition on. The gauge won't lie! It will then confirm or absolve the tank pumps from blame.

Have you also coded the quantity correction values into the ECU from the replacement injectors?

You may need STAR diagnosis to help you proceed.

Hi Steve,
Grateful for your suggestions.
We are gonna start tomorrow with the "big boy" again(R320 CDI).
Of course first steps will be the ones you mentioned.
But as I declared before; long cranking occurs only after a few hours of stay.
Once the engine starts; long cranking and difficult start never repeats during the day.
I' ll keep you updated about the "big boy".
Thanks again.
Salih

 

[salihdeniz]

Aha in that case, sorry for the wrong info OP

No problem Alexander.
Fingers crossed; we' ll back on R320CDI tomorrow.
Take care.
Salih

 

[salihdeniz]

Hi Steve,
Grateful for your suggestions.
We are gonna start tomorrow with the "big boy" again(R320 CDI).
Of course first steps will be the ones you mentioned.
But as I declared before; long cranking occurs only after a few hours of stay.
Once the engine starts; long cranking and difficult start never repeats during the day.
I' ll keep you updated about the "big boy".
Thanks again.
Salih

Dear Steve, Dear Alexander and Dear All,

The long cranking issue on our 2007 R320CDI has been solved.
We' d replaced all of the glow plugs on May 2017 but not with the original spare parts.
What a mistake!!
Thanks to the cihef mechanic of the Ferser Garage in İzmir TURKEY;
We had dismounted one of the glow plugs, fed with the neseccaryvoltage and measured the time for gettig the edge of the glow plug in red colour.
The existing glow plug took approx. 7 seconds.
We tried the same process with the original glow plug and it took less than 2 seconds.
We replaced all of the glow plugs with the original ones, left the car for three day without starting it.
Yesterday afternoon it started like brand new.
I am grateful for all of your suggestions.
Have a shiny sunday.
Salih

 

[Frontstep]

My older 320cdi starts quickly without glow plug warming time ?