Starting issues when cold om642

[BlueRubber]

Hi all,

Got a s212 e350 facelift 120,000 miles. Sometimes the car takes an unusually high amount of cranks to start when cold.
The battery was replaced earlier this year.
The fuel filter was replaced with OEM 12,000 miles ago ( less than 2 years ).
As far as I know, the glow plugs have never been replaced.

Any ideas on what to check next?

 

[W1ghty]

New glow plugs and a new relay module should see you sorted for a few years .

 

[Smiley]

The glow plugs are easy enough to check with a multimeter - the resistance should be a small single digit ohm value - if it shows a high resistance or open circuit then it is dead. If the plugs are OK then it is most likely the relay - check to see if there is 12v at the plugs. If you are going to change the plugs yourself then do them hot and with patience; they can snap and you will have created yourself a much bigger job at that point. There is no point changing a working plug unless you are paying someone else to do it and then it may make sense to have all 6 done at one time.

 

[W1ghty]

Hi all,

Got a s212 e350 facelift 120,000 miles. Sometimes the car takes an unusually high amount of cranks to start when cold.
The battery was replaced earlier this year.
The fuel filter was replaced with OEM 12,000 miles ago ( less than 2 years ).
As far as I know, the glow plugs have never been replaced.

Any ideas on what to check next?

You have an excellent MB specialist just outside Reading.
Ian at Star Services .

 

[toteimerced]

If one’s gone, the rest won’t be far behind.

 

[DSM10000]

If a glow plug or plugs are faulty the glow plug light in the instrument cluster normally illuminates for about 30 seconds after starting.

 

[BTB 500]

As above you should know from the cluster if there's a problem with the plugs or relay (the latter normally causes the glowplug light to come on after the engine has started and stay on for a minute or two). I ran my OM642 with two failed plugs for a year and it started fine, even in winter. The first glowplug on mine failed at 35k miles ...

But. There's a 225A 'mega fuse' for the glowplug circuit which will knock everything out if it blows. Worth finding & checking that as cold starts would take some cranking with no plugs at all working.

 

[DSM10000]

As above you should know from the cluster if there's a problem with the plugs or relay (the latter normally causes the glowplug light to come on after the engine has started and stay on for a minute or two). I ran my OM642 with two failed plugs for a year and it started fine, even in winter. The first glowplug on mine failed at 35k miles ...

But. There's a 225A 'mega fuse' for the glowplug circuit which will knock everything out if it blows. Worth finding & checking that as cold starts would take some cranking with no plugs at all working.

I had the light on for a time after starting. Two failed plugs as with you but it still started promptly.

I believe that the glow plugs stay on after the engine has started for a time to help reduce emissions

 

[BTB 500]

I believe that the glow plugs stay on after the engine has started for a time to help reduce emissions

Yes I read this somewhere and it makes sense I think.

 

[BTB 500]

Just as an aside the glowplug circuit got disconnected on my tractor (3 cylinder Mitsubishi engine - half an OM642?!), and that wouldn't fire at all when cold no matter how much it was cranked Filled my storage shed up with what looked like steam - unburnt atomised diesel puffing out of the exhaust

 

[Smiley]

If one’s gone, the rest won’t be far behind.

not my experience. I used to change one or two at a time; over many years there was no consistency at all, some cylinders had two changes others one or none. And always beru plugs. Might make sense to change all if paying someone else though.

 

[BlackC55]

Its probably just the relay.

We had one recently that went wrong and took out all of the glow plugs twice. So in some cases a new relay and set of glow plugs is needed. Not a cheap job nowadays.

We tend to replace glow plugs one at a time because of the risk of snapping them in the head. Steel glow plug and aluminium head doesn't mix well. Wen fitting we use high temp grease on the threads and some at the bottom of the plug at the seat.

 

[BlueRubber]

Thanks for the info everyone. I try to do as much as work as possible myself on vehicles, so bear with me ...
My understanding is that I can test the glow plugs with a multi meter set to resistance from the connector that goes to the relay module.
Could someone please post some instructions on how to do this?
Which pins am I testing and is the other end of the multi meter going to the chassis ground?

If any of the plugs do need swapping I'd probably take the car to a garage given the risk of them snapping in the block.

 

[W1ghty]

Thanks for the info everyone. I try to do as much as work as possible myself on vehicles, so bear with me ...
My understanding is that I can test the glow plugs with a multi meter set to resistance from the connector that goes to the relay module.
Could someone please post some instructions on how to do this?
Which pins am I testing and is the other end of the multi meter going to the chassis ground?

If any of the plugs do need swapping I'd probably take the car to a garage given the risk of them snapping in the block.

YouTube . Just search “testing glow plugs with a multimeter “

 

[T5R+]

OP, have you had the battery thoroughly checked out?

 

[Smiley]

Thanks for the info everyone. I try to do as much as work as possible myself on vehicles, so bear with me ...
My understanding is that I can test the glow plugs with a multi meter set to resistance from the connector that goes to the relay module.
Could someone please post some instructions on how to do this?
Which pins am I testing and is the other end of the multi meter going to the chassis ground?

If any of the plugs do need swapping I'd probably take the car to a garage given the risk of them snapping in the block.

To check the glow plug you need to measure it's resistance - one lead from the multimeter on the centre of the glow plug and the other lead on an earth point. It should be a few ohms - I don't know the exact spec but somewhere in the range of 5-10 ohms. When they fail they tend to read either very high k ohms or completely open circuit ie 0 resistance between the power connection and earth. In either failure mode it won't heat up.

 

[Smiley]

Oh and careful who you take it to if you get someone else to do it. It's a job for a patient mechanic who is prepared to work them backwards and forwards - if you get the "I don't really give a f*** it's not my car" mechanic who is just going to say sorry it snapped.....
Some techs break very few, others make a mess.

 

[BTB 500]

To check the glow plug you need to measure it's resistance - one lead from the multimeter on the centre of the glow plug and the other lead on an earth point. It should be a few ohms - I don't know the exact spec but somewhere in the range of 5-10 ohms. When they fail they tend to read either very high k ohms or completely open circuit ie 0 resistance between the power connection and earth. In either failure mode it won't heat up.

I've never actually looked at one, but curious about how they fail with high resistance? I always assumed there was just a heating element (resistance wire) which is either intact/connected or not ... in which case you could just use a continuity tester??

Oh and careful who you take it to if you get someone else to do it. It's a job for a patient mechanic who is prepared to work them backwards and forwards - if you get the "I don't really give a f*** it's not my car" mechanic who is just going to say sorry it snapped.....
Some techs break very few, others make a mess.

100%

I've actually had dealers refuse to change them if the engine is still staring OK. My local garage uses a vibration gun (more delicate/precise version of an impact driver) to loosen them, but still no guarantees!

 

[W1ghty]

This is why I change my glow plugs every 3-4 years and apply some high temp paste to the threads. It’s been a cheap job with Bosch or Beru bought in sales (£40-60).
Almost guarantees that they come out .

 

[BlueRubber]

YouTube . Just search “testing glow plugs with a multimeter “

Thanks I found out how to test the glow plugs directly, but I'm looking for some information on how I can test them through the connector that goes to the relay module.
ie. what are the pinouts for that connector? As it's going to be a lot easier to test that way than by checking each plug directly due to access.