W204 350CDI cold starts issue

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zima25

New Member
Joined
Jul 24, 2021
Messages
3
Location
Czech republic
Car
W204 350CDI 195Kw 2012
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.
 
W204 350CDI - spark plugs check - OK. First diesel I have heard of with spark plugs.
Are the glow plugs or relay working OK?
 
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.

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

If it was checked on a proper MB Star diagnostic then it would have identified if the GPR was at fault and any faulty glow plugs.

The GP`s are not expensive and if they are out then i would just replace them with new ones.

K
 
A basic diagnostic machine would bring up codes for a faulty glow plug module.. pretty sure for glow plugs also
 
£37 each for my 350 glow plugs .
 
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.
 

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