120Cdi Starting Problem in the cold

[Paul Ben]

Morning all this is my first time on the forum as I am at a lose end
I have the Merc Vito 120Cdi Sport 2008 model, this winter (not that its that cold yet) the van is becoming harder to start, it has always started very quickly but now turns over 5-6 maybe 7 times before coming to life, the other morning it started on the 5th attempt (the first 4 times it just turned over then timed out and the 5th time it started). Its done 80k and last serviced in Aug this year, I have read reports saying the fuel filter could be getting block so this was changed yesterday and no difference. I have had the van on a diagnostic and no fault codes were showing, rail pressure is good and no leak off from the injectors. The glow plug module was replaced last winter but I guess there is no way of testing this is ok? The glow plug light illuminates for 3-4 seconds then goes off when first starting the engine so I guess this is normal. I have been told by a merc mechanic that if a plug or the relay was faulty there would be a malfunction on the dash and or the light would remain on. I normally use supermarket fuel and never had a problem with any of the diesel cars I have owned.
Any help ideas would be great.

Thanks Paul

 

[mersum1es]

I still think it's fuel pressure problem. Injectors have to leak a bit (tank line leak) in order to work, but if leak is too high it shows worn injector. Leak test is easy to DIY. Electrical correction values should have been checked too via SDS tool.Fuel quantity valve has sometime been culprit too. How rail pressure was checked, during failed start attempt? Remember to do all tests under same conditions when start problems happens.

Usually glow plug light should show plug/relay faults. But plugs of some engines are PITA to measure, so usually they are changed all together when problems occur.

 

[Paul Ben]

I think I will need to get over to the merc specalist. The rail pressure was checked after me driving it to a local garage so the van had run for 2-3mile. What is the SDS tool? is this star as the local garage don't use this but the rail pressure on tick over was 250 - 260 bar. It would not start again this morning it actually killed the battery in trying, but with a jump start it started no problem.

Thanks once again

 

[mersum1es]

2-3 mile drive can make difference. If it started, of course there is no problem Car should be left waiting outside garage and tested cold = no start situation.

Yes SDS = Star Diagnostic System. Star has guided testing procedures for different components, some of them can be done if only all components can be controlled via another program and user knows what to do. I'm not sure can they show correction values. Injector tank line leak test needs no special equipment.

 

[Paul Ben]

Ok, it looks like I need to leave with the merc guys over night then, FYI I have today removed the glow plug relay connector and tested each cable going out to the plugs all of which came back with 0.6 ohm so they seem ok (unless failing under load). The only problem is I cannot check to see how long the relay is energised for as it may not be enough. For piece of mind in the morning I was going to hitch up another car for its first start, although I am 95% happy the battery turns over quick enough, I thought this would be a way to ensure plenty of power (starer motor turning quick enough) from the outset, as surly if the high pressure pump is conneted to the cam (assuming no leaks and not worn) I am thinking if its spinning fast enough the pressure should be at the required level. Then if this fails it looks like another trip to the garage. Thanks for your input.

 

[Paul Ben]

2-3 mile drive can make difference. If it started, of course there is no problem Car should be left waiting outside garage and tested cold = no start situation.

Yes SDS = Star Diagnostic System. Star has guided testing procedures for different components, some of them can be done if only all components can be controlled via another program and user knows what to do. I'm not sure can they show correction values. Injector tank line leak test needs no special equipment.

Hello again we spoke a while ago regarding my vito, a few checks have been done and the rail pressure is fine, a leak off test was also carried out and although SDS showed nothing out sync but with a manual test I have been told the 3 injector are letting by? One question I have, would this not cause starting problems every time and not just in the cold weather (below freezing) and would I not be getting lots of black smoke, lumpy idling and bad fuel economy as I have none of these, i just want to be sure as the cost to replace the injectors is quite a bit of money.

 

[mersum1es]

Hello again we spoke a while ago regarding my vito, a few checks have been done and the rail pressure is fine, a leak off test was also carried out and although SDS showed nothing out sync but with a manual test I have been told the 3 injector are letting by? One question I have, would this not cause starting problems every time and not just in the cold weather (below freezing) and would I not be getting lots of black smoke, lumpy idling and bad fuel economy as I have none of these, i just want to be sure as the cost to replace the injectors is quite a bit of money.

Injector tank line leak is very often temperature related and happens only at first start of the day. But in no start situation lack of sufficient rail pressure should be seen in star test... Then if even slightly warmed injector, it tightens itself better.

You should get refurb injectors around 150€ piece...

Hope you'll get it sorted!