CLK320CDI Hard to start cold

[SamJ83]

Hi, I'm hoping someone could give me some advice on my 2009 CLK320CDI which is hard to start when cold. I have had new glow plugs and new battery but the only way I can get the car to start after normal pre warm is to warm glow plugs twice then it'll start fine. My local garage has done all checks on glow plug module and glow plug relay and has told me they can't find any codes and all seems ok? I've tried fuel treatment to clean system clutching at straws without any effect car is very well looked after and does 60 miles per day so gets good run, I'm now at total loss and any thoughts would be great help.....Thanks

 

[M80]

Watch live readings on fuel rail pressure while attempting to start.
Injector leak off test might show excessive leak off causing a failure to build pressure fast enough.

 

[SamJ83]

Watch live readings on fuel rail pressure while attempting to start.
Injector leak off test might show excessive leak off causing a failure to build pressure fast enough.

Ok thanks , I've been told checks have been done on diesel run back but unsure if they did live readings?? I'm trying to book Mercedes specialist near me they may have come across this before on these engines, I'll run this by them

 

[supernoodle]

If by warming glow plugs twice you mean ignition on-off-on then crank, that can't be injector leak off related. Leak off is the spill from the HP fuel side of the injector to the LP. There is no HP fuel until you're cranking.

When you ignition on you'll have glow and the low pressure pump will prime for a short duration. So if you are meaning key on off on you need to isolate which of these is helping.
Don't know what country you are on but it's not cold enough in the UK that glows should be really necessary at the moment.

 

[alexanderfoti]

If by warming glow plugs twice you mean ignition on-off-on then crank, that can't be injector leak off related. Leak off is the spill from the HP fuel side of the injector to the LP. There is no HP fuel until you're cranking.

When you ignition on you'll have glow and the low pressure pump will prime for a short duration. So if you are meaning key on off on you need to isolate which of these is helping.
Don't know what country you are on but it's not cold enough in the UK that glows should be really necessary at the moment.

+1 if you have to pre glow twice, it's likely that the module is failing or the plugs are not getting as hot as they should. I see many modules that fail without codes.

Keep in mind the v6 diesels are relatively low compression and will not start when cold, without glow assistance, even when it's warm outside.

 

[Doug1234]

Maybe they did check relay and plugs out or because they found no codes for either presume all is ok…. But anyway here is how to check them out and the relay if you need too. I know it’s a Jeep but engines the same

 

[pgh13]

I'm sure I've read that there are 2 specs of glow plug; one for 7 volt and one for 12v. Is it possible that 12v plugs are fitted when they should be 7v?

 

[SamJ83]

If by warming glow plugs twice you mean ignition on-off-on then crank, that can't be injector leak off related. Leak off is the spill from the HP fuel side of the injector to the LP. There is no HP fuel until you're cranking.

When you ignition on you'll have glow and the low pressure pump will prime for a short duration. So if you are meaning key on off on you need to isolate which of these is helping.
Don't know what country you are on but it's not cold enough in the UK that glows should be really necessary at the moment.

I'm in the UK and yes has to be at least 20c for it to start when cold on single ignition on then crank for it to start ok. Thanks for replying have gathered a lot of helpful information on what action to take next to resolve this problem.

 

[SamJ83]

I'm sure I've read that there are 2 specs of glow plug; one for 7 volt and one for 12v. Is it possible that 12v plugs are fitted when they should be 7v?

Could be for sure , I'd like to think my garage had fitted like for like but these days you never know! I will check my bill to see if any details were recorded about what was fitted? but I'll make note of this as possibility.......

 

[SamJ83]

+1 if you have to pre glow twice, it's likely that the module is failing or the plugs are not getting as hot as they should. I see many modules that fail without codes.

Keep in mind the v6 diesels are relatively low compression and will not start when cold, without glow assistance, even when it's warm outside.

Thanks that is very interesting! would you say just try new module or relay and module together?

 

[Doug1234]

Glow plugs for the om642 are 4.4 volts

https://www.hkt-jp.com/images/glow_plug_catalog.pdf

 

[pgh13]

Just out of interest, has it always had this problem while you've had the car or did it start at some point and did anything immediately precede it starting?.....
Or not starting ?

 

[SamJ83]

Just out of interest, has it always had this problem while you've had the car or did it start at some point and did anything immediately precede it starting?.....
Or not starting ?

I've had the issue for 12 months odd now but it didn't have problem when I first bought the car in 2019. I have found / tried just recently that doing one pre-warm of glow plugs and then when light goes out just leaving it extra 3-4 seconds before cranking over does seem to be helping and staring has improved. The warmer weather now is helping so that plays a big part but I'm sure it still isn't right and come the winter will have to get it checked out if I have to return to doing two pre-glow before cranking

 

[mioba]

Has it been to a MB specialist yet?
keep us updated