Please, I need some help to fix my first mercedes 190D, 2.5L.
It starts very nice and smooth and after 1/2 minute it starts misfire at idle and below 1500rpm, pinging noise ( this sound is detonation), with blue smoke and knocking noise.
When it is warm, the idle is ok, but a little smoke still with pinging and knocking noise.
Also, I noticed the fuel injector pump return line which connects the injectors return lines has fuel going to the oposite direction with some pressure.
I found that by disconnecting the return line between the fuel filter and number # 1 injector with running engine.
Is this fuel back pressure normal in the return line between the fuel filter and the # 1 injector?
At that time no fuel was coming out from the injectors return lines.

I changed the fuel filter, injectors and prechamber are fine no leaks. I wonder if I have to refurbish the cylinder head or fuel system problems.

Again please, what is the next step should I follow to troubleshooting those problems.
I appreciated any help, thanks you all

The fuel pressure in the return line is OK.

Try to narrow down whether you have a single cylinder problem or a systematic problem. Crack each line while running one at a time. If the engine doesn't change running each time then you have found a cyl with a problem.

__________________
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

Hello Stevebfl

Thanks for your replay and appreciated very much it and is nice to know that we all ways find some one out there for help.
I had done this before and all cylinders work fine. The smooth start does only once at cold start, after that the engine is very noise. But if I start next morning it start nice smooth and after 1/2 minute the noise is back again with smoke.
I just bought a used cylinder head for refurbish, but I would like to know for sure what is going on with that engine, before replace the cylinder head.

Again thanks for your information and I'll keep trying to see what is next.


Tulio