Hi all diesel freaks!
My friend owns a W124 300d -91 and has some problems.
it all started when he ran out of coolant, and the engine overheated
he fixed the radiator but the engine is knocking harder now, and smoking black at idle.
first we thought an injector had stuck, so i loosened one line at the time but couldn't notice any major difference between the cylinders, the knocking was still there.
And when the engine is cold, it's hard to start, and when it starts it runs good and silent for 15-30 seconds, then it starts to knock harder. i recognize the sound as an advanced injection timing, i have quite good diesel experience and had a volvo 940TD, on that engine there was a thermostatic cold starting device that advanced the timing 4 degrees when the engine was cold, and as it warmed up, it went back to normal timing.
i wonder if there is something like this on my friends mercedes?
it's not that easy to see the injection pump under the intake manifold, but there is at least 2 vacuum controlled devices, and 2 electrical connectors at the back, the upper connector seems to be the stop solenoid as the engine dies when it is disconnected, but if i disconnect the lower one nothing happens, neither does it happen anything when i disconnect the vacuum hoses.

so how is the cold start timing advance controlled?
it seems to be a ****load of vacuum/electric control stuff on this engine compared to my volvo. and incerdibly bad space around the engine!

Greetings from Sweden!

 

I would put some thought into the fact that your Engine is supposed to start and run properly just as it came from the Factory.

The only cold starting aid on your car is the Preglow/Glow Plug system.

The only device to advance your timing is the Fuel Injection Pump Timer (centrifugal weights) on the drive end of the Fuel Injection Pump.

There is no other advance.

If your Engine has an Aluminum Cylinder Head they do not take kindly to being over heated.
It would be interesting to do a compression test.
It also would not hurt to check your Glow Plugs. The Diesel Giant website has a pictorial on how to do that. It is not for your year and model of Engine but the way it is done is the same.

Are any computer codes showing?

 

You did not mention if the Knock sounded like a Rod Knock or not?

Also I have found on my Mercedes that late timing will cause a Fuel knock and so will too advanced of a timing.