C250D knocking and smoking.

[munstermerc]

Ive had my C250D for 2 years and its been great up until last month. Its a '98 non turbo, 5 cylinder diesel. I began to have trouble with air in the fuel. After the car sat overnight I had to crank the starter continuously to purge the air out of the system before it would start. I changed the fuel filters and checked all the fuel line connections and replaced a couple of o rings that looked suspect including the one between the stop switch and the injector body which I hadnt realized was there previously. However none of this helped.
I took the car to a local garage and the mechanic there detected leakage from the connections on the top of the injection pump. He tracked it down to the no.5 cylinder pipe connection He removed the pipe and the metering unit ( or whatever it is called), replaced an o ring which looked very ragged. He refitted the pipe and metering unit. The car is now starting better, although not perfectly but knocks and smokes very badly. The smoke is blue and is particularly bad when the engine is cold. The knocking does not seem to come from any particular cylinder and loosening the injector pipes one by one does not identify the source of the knock. Ive run out of ideas and need help please.

 

[Dieselman]

If cracking free an injector pipe doesn't fix it it's not an injector issue, although knocking indicates it is.

Did this smoke only come on after the delivery valve seal was replaced or was it here before.?
Pull the breather pipe off and see if it's breathing heavily. That would indicate ring wear.
Next step would be a compression leak down tests.

Check the EGR valve is functioning properly. Try disconnecting the vac line as a test, or permanently.

It could still be air in the system, check the feed pipes thoroughly.

 

[bolide]

I think you need to put the car in front of someone who really knows what they're doing. It's possible to waste lots of time (=money) on this kind of thing

Nick Froome
www.w124.co.uk

 

[Number_Cruncher]

>>but knocks and smokes very badly.

This is quite a common problem after a delivery valve O ring replacement.

It's probably worth doing it again - there's a copper crush washer in there that should be replaced (but many don't even know it's there), a lapped joint which is all too easy to disturb, and a 3 stage torquing procedure which many don't follow correctly, and even a speck of dirt will ruin the job - lots to go wrong in other words.

I know that Dieselman thinks that delivery valves are easy to re-seal, but, I'm quite wary of them.

 

[Dieselman]

But the O-p said cracking an injector didn't stop the smoke. If only one valve was disturbed it should only affect one cylinder.

Worth a look though, as you say.

A quick check is to feel the injector lines, you should feel them knock with each injection, if one is soft then that's the faulty one. A listen with an engine stethoscope would probably reveal a dodgy valve or injector.

 

[Number_Cruncher]

>>A listen with an engine stethoscope would probably reveal a dodgy valve or injector.

I think that's really good advice - well worth following up on.

 

[munstermerc]

The engine was running perfectly before the delivery valve seal was replaced, no smoke or knocking.
Ive checked the breather and the dipstick tube, both ok.
Ill check the ERG valve tomorrow and report back.
There is still air in the fuel system, I can see it in the transparent fuel pipes which are all brand new. all of the o rings on the fuel pipes are new as well.
The mechanic did not replace the copper crush washer, he refitted the old one, could that be the source of the problem?
Just from the feel of the injector lines the knocking seems to be coming from cylinders 2 and 3 but its quite vague. I dont have a stethescope but I may be able to borrow one.
Thanks a lot.