W204 350CDI cold starts problems

[zima25]

Hello everyone. I would like to ask for help with following problem on my W204 350CDI 195Kw 2012 203 000km, VIN: WDD2042231F910844. Thank you very much for any tips.

Bad cold starts - longer cranking (5 - 10s), when starts, engine is running not very smoothly for approx 20- 30s, then its OK. Littlebit of white smoke. Only first start is bad, then all day OK. Car must stay at least 8 hours for bad start again.

What has been done:

• new battery (main one in trunk)
• new starter motor
• new fuel filter (and others filters, engine oil, etc...)
• spark plugs check - OK, battery check - OK

Still same problem.

• injectors - test - one was a bit clogged - cleaned - then test OK
• CR pump - test - OK
• fuel tank cleaning
• all fuel lines cleaning
• new fuel hoses
• new fuel filter again
• new low pressuer pump
• new DPF filter
• exhaust system cleaning
• magnetic metal shaving catcher installed
• new fuel pressure regulator on left rail module (tested also with complete left rail module from another car)
• everything set up using original diagnotic equipment
• all new gaskets, sealings (injectors, CR pump, etc...)
• diagnostic shows no errors
• everything checked by professional MB mechanic
• cylinder compression check - OK
• everything else is OK, car works perfectly

Cold starts still bad, but now with NO white smoke

- injectors tested again - OK

It seems to be a problem with low fuel pressure while engine is cold, but somewhere after CR pump, fuel pressure on CR pump is OK

Thank you for any tips

 

[mersum1es]

Change the garage if they have checked 'spark plugs'.... ok they might refer glow plugs...

What is 'injector testing'? Sounds like too much tank line leak as its most common culprit. IF that is ok, electric correlation values (I think THIS has been cheked now).

Has fuel quantity valve been tested?

Then - does 'double ingintion cycle' help? Is low pressure level tested (no clogged aux pump)?

 

[bembo449]

as above , replace the glow plugs or at least have them out and test , you need to rule them out

 

[zima25]

My mistake, I wrote wrong. Glow plugs, of course. They have been taken out yesterday, so by Monday I should know the result of test. Before they were only tested installed by voltmeter and vaules were OK, but there might be some other issue with them, I dont know.

Double ignition does not help. Aux pump is new and tested.

Dont know if fuel quantity valve has been tested, but I assume so as they have tested really everything in past ten weeks.

Tank line, if you mean the left one with fuel pressure valve is currently installed working one from another car and cold starts are same.

What you mean by electric coleration values? Which ones?

Thank you

 

[mersum1es]

I mean injector tank line leak test. That most common culprit for low rail pressure. I assume that has been investigated and found a culprit? If not then things go complicated...

Thre is electric correlation values (mm^3/hub or um/hub) for every injector). High value indicates internal leak / bad compression/ anything that ecu thinks injection amount should be increased. That should be checked in situ.

 

[zima25]

Injectors test has been done in another garage, in specialized diesel center and all values were in tolerance. No leak found. Unfortunetally in this case.

 

[Doug1234]

This screams glow plug relay failure /part failure to me, has the actual relay been checked ?.

 

[zima25]

Don´t know how to properly check the glow plug relay. Maybe it will be necessary to purchase a new one and try.

 

[zima25]

Solved! Three glow plugs and glow plug relay were broken. All new NGK glow plugs and BERU glow plug relay (and for sure also new cooling temperature sensor) and cold starts are OK.

 

[Doug1234]

Nice result eventually , You would be wise to find another garage / mechanic in the future because you have spent a fortune on something that is a simple fix.

 

[zima25]

Well, the problem was not only cold starts, but also the exhaust was very dirty and the car sometimes behaved weird - slow throtle pedal reactions, etc... I think that the fuel system cleaning was not useless as also the fuel analysis showed dirt in the fuel.