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

NZ-Merc

Hi,
As a possibility might be worth properly testing the engine computer temp sensors just incase when it is fully cold the computer is getting air or water temp signals saying the engine or air temp is still hot and trying to start cold with no cold enrichment.


You mentioned no fault codes, was this with an aftermarket scanner or at a Mercedes dealership?
I would think at this stage if it was not at a dealership, it would be money well spent getting it scanned and left overnight there so they could experience the problem and diagnosis it.

zima25

Hi,

yes, temp sensors have been checked and they work correctly. This garage is not a dealership, but they are MB specialists since 1993 and they have proper diagnostic equipment. Going to dealership is really the last step as it is quite expensive and dealership here does not have very good reputation. But the true is that current bill for these repairs is approx 4 500EUR so if it will be 5 of 5,5 it does not make such a difference anymore

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.