Strange engine problem - help

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New Member
May 30, 2011
Swindon UK
Mercedes E320cdi E350cdi & SLK350 (W211, w212 & R171)
Driving yesterday engine at normal temperature accelerated off a roundabout bit of a bang then loads of smoke and a nasty metallic noise coming from the engine. Dead engine right. That's what I thought. Horrible day pouring with rain. Contacted the break down company, when the driver arrived he had quick listen to the engine and agreed it was toast. Got it towed to a mechanic friend of mine as it was late decided to drop it outside ready for the morning. Next morning towed it in to the workshop. Started it to show my mechanic the noise. Well started perfect, no noise, no smoke. Even revved it to 4000rpm no problem.....
Then once warm 6 or 7 mins boom knocking returned and loads of smoke. Filled the workshop. We are stumped. Any ideas.
Of course the car is not usable and my mechanic says it's dead. But why no metalic noises when cold. Surely if there was a mechanical failure it would show even when cold.
Car, engine, details etc please.

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My guess- the normal flow of gases through your engine is compromised in some way leading to excessive cylinder pressure build up / incomplete combustion could be a blocked catalytic converter/ dpf or a broken EGR system. Other possibility might be a leaking head gasket allowing coolant into the combustion chamber when the engine is warmed up? If it runs OK when cold then points to no immediate mechanical damage--- for now--- check the cooling system for excess pressure and engine oil for contamination or excessive unburnt fuel or coolant.
Sounds very much to me as if your engine is being over fuelled. My development engine has suffered this as a result of the ECU.Diesel knock is so loud one would suspect a big end had it been a petrol. I don't know about the pump on your car but certainly the common rail will have a pressure regulating valve. This is driven at a set frequency that varies the square wave in milliseconds to alter the pressure allowing varying amounts of fuel to return to the tank. This should have a known resistance that you can test with a multimeter. Also on the rail is a pressure sensor that measures the rail pressure. As mentioned before I don't know about the pump. Some have a solenoid valve to reduce the flow rate at tickover.
I think an Indy with Star or someone with Launch diagnostics would get you pretty close.
Another thought is a fracture in the EGR cooling circuit allowing water ingress. This could coincide with warm engine ( thermal expansion) and valve opening. It's only a thought and probably not the case but worth checking water levels.
When head gaskets go between cylinders they can sound really bad as well!
Thanks for the responses
E320 2004 W211 - is that enough detail or would engine number help
I did think of the EGR system but don't know enough to be able to check it
I do agree I find it difficult to believe actual mechanical damage that does not show when cold!
Thanks Tim 203. I like the common rail suggestion. I did actually have a common rail error code with engine management lamp come up a couple of weeks ago. At the time I thought nothing of it and simply reset it in diagnostics. I try and look in that area. Cheers.
Millfed you still haven't told us what engine it is - E320 diesel or petrol??

Surely a 320 with common rail must be diesel?

Don't think MB had a 320 CGI petrol engine in W210s and W211s.

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