OM642 glow plug relay failed but no code?

[Anything101]

It’s a 2006 224hp version (CLK).

I assumed the car wouldn’t try to start until it is ready - good to know.

From my previous post, is the behaviour what people observe from out of spec injectors? Or what else would cause the symptoms to occur in that particular window?

 

[Supernoodle]

55deg certainly isn't glow plug territory.

Injection pattern (number of pilots/mains/posts) and timing changes dependent on temperature. I guess at 55 there's a change of either or both such that the in cylinder temperature profile change enough that the excess isn't getting burnt.

 

[BTB 500]

I assumed the car wouldn’t try to start until it is ready - good to know.

That would give prolonged cranking in cold temps, even if everything was working properly. If you stop the key before moving it to the start position does the plug light stay on for a couple of secs. and then go out?

 

[Anything101]

That would give prolonged cranking in cold temps, even if everything was working properly. If you stop the key before moving it to the start position does the plug light stay on for a couple of secs. and then go out?

No. I know the bulb works because it lights up with all the others (e.g SRS), but it never stays on longer than that. No matter what the temperature is.

So the consensus is that I should get the injectors inspected? Is it possible to rebuild these injectors? I’ve seen varying opinions, but many of the threads are quite old now.

 

[m80]

During my 642 saga some years back,
I had all 6 injectors checked, 5 good, 1 had an electrical issue. I would have expected that issue to be apparent while driving, other than smelly smoking.

Anyways 6 supposedly good injectors fitted my smoking issue, as you describe, remained.
New MAF, new DP sensor, new DPF......... Really trying anything in hope.
I found electrical issues, as in poor unreliable connections, to turbo actuator, EGR, and 1 more I forget. It was obvious by now that a previously there had been some one shoving test probes into the connectors and splaying them.
Still not cured.
Eventually a well respected Indie fitted 6 new injectors, updated software, no bloody difference, within 2 miles of his workshop it attempted yet another regen.
He suggested that previously when he was unable to resolve such a problem a remap did, it didn't.

I experienced high sump pressure, so assumed the bores were passing. I sold on with full honest description.

 

[Anything101]

I saw another thread on here about a c250 with a misfire. One of the replies suggested low compression which causes incomplete combustion at that particular window of operation. If that were the case, it would likely scrap this car.

As it’s a diesel, full throttle simply means injecting lots of fuel. So would low compression not be symptomatic at WOT? Or any other time?

I’ve had 3 other cars which use variations of this engine and this one feels very similar in terms of power delivery and smoothness.

 

[BTB 500]

No. I know the bulb works because it lights up with all the others (e.g SRS), but it never stays on longer than that. No matter what the temperature is.

My glowplug light appears to come on for a fixed length of time once the ignition is on, regardless of engine or ambient temperature. But if yours doesn't do this it could well be a failed relay, which would explain the poor cold starting.

Regarding the injectors ... out of interest, how many miles has the car done? If you run it on standard diesel then a couple of tanks of V-Power or similar (containing a good detergent package) wouldn't hurt, and there's a small chance it might help. Other cleaning additives are available of course, but IIRC MB say not to use them (although I suspect plenty do, without any issues).

FWIW my OM642 is a 204 bhp version but similar vintage to yours (2007) and approaching 160k miles. I run some V-Power through it now and then, just in case.

 

[Anything101]

Close to 150k miles. I’ve run an additive through it some months ago. I think it probably reduced the severity of the smoke/rough running under low load. I could give it another go, but it definitely didn’t cure it so I will need to do something else anyway.

The car is run on normal shell diesel, it may be confirmation bias but this seems to reduce the occurrence of the issue as well.

I went out in the car today. The glow light comes on for 1 second (timed) and then I don’t see it again. All the other lights stay on - I only ever paid attention to the glow light.

 

[TeddyRuxpin]

Sorry to ask the obvious, but does a 2006 CLK actually have a DPF? I thought they were Euro 4 with no DPF...

 

[Anything101]

I’ve checked the paperwork. I have option 926. DPF is 474, so that’s 1 less complication. Thanks.