E 300 td diesel knock

[johnsco]

http://www.mbclub.co.uk/forums/howto/46736-howto-diesel-delivery-valve-leaks.html

This link to the "HOW TO" section of this forum will tell you just about everything you need to know about the job.
It's certainly possible ... albeit a bit complex.
Cleanliness is pretty-high-risk in my assessment.
Also - You will have to replace the seals and crush washers.
You don't know which one(s) are the problem.
You will have to re-fit all six.
Also - I understand that success is not always 100 per cent, even if the job is done correctly with proper cleanliness.
If it has to be done - Then it has to be done.
I hope it goes well.

 

[runningman]

Thanks Johnsco

Not going to tackle this job till next week, going to run a diesel purge first using Liqui Moly to see if that will shift the dirt if there is any.

 

[Dieselman]

It wont. That is for deposits of gum not particles.

As long as you ate careful there will be no issues doing the delivery valve O rings.

I doubt it is the problem.

 

[runningman]

Dieselman.

what's your thoughts on this problem, if you don't mind me asking.

Thanks

 

[runningman]

carried out a diesel purge this morning using liquid moly and within 2 minutes the knocking was completely gone. Engine sounded brand new. Purged diesel for about 10 minutes, then connected fuel lines back up and took car for a spin. When I got back home I let the engine idle and the knock was there again but sounded a lot quieter. Rev the engine and it sounds beautiful.
So now I know for sure that the problem is with the pump.
Why did the knock go away when using liquid moly? is it because its more oily than diesel?
I can still see bubbles travelling along the fuel pipes even though they have all been replaced with MB parts.

????

 

[Dieselman]

The noise went because liquid Moly has a higher cetane value.

Try running a tank of injector cleaner.

 

[runningman]

As there are still air bubbles in the system, surley this would cause a drop in fuel pressure at the fuel delivery valves therefore the injectors won't operate at the correct pressure!

Because i have replaced all fuel lines and filters with MB parts, you would think the O rings on the fittings will be up to standard. Maybe the're not.
If you look carefully at the point where the fuel pipe fitting enters the top of the pre-filter from the flow side, you can see it wet with diesel. Some of the other fittings are showing signs of this wetness as well.

Are MB 'O' rings too small for the apertures that the fittings fit into? causing them to weep fuel, hence the air bubbles. Will change them for VITON 'O' rings, see if they make a difference.

Where else could the air be intrained from? Also, when you switch off the engine the fuel drains back about an inch from the pre-filter to the fuel heater.

Ive read that some air the system is normal but surely that can't be right?

 

[Olivier]

There is the heat exchanger that can draw air and the pre'filter.
Where are the bubbles starting from?

 

[runningman]

Olivier.

the air can be seen in the lower most fuel lines and also the one from the filter head to the top of the SOV.
Can the fuel heater be bypassed? is it really needed.

 

[Olivier]

If you see the air coming from the filter head this is not the heat exchanger but the prefilter assembly. I had this on mine too, took me a long time to realise it was the assembly there...
All prefilter assemble leak some how. Some more then others. The proof is that once you stop the engine and let it sit for a while, there is always a little pocket of air in the top clear line after the prefilter. This has to be coming from somewhere...

First you could try to put some PTFE tape around the 3 Orings.
Clear pipe, filter and the second clear pipe.
The extra layer might do a better tighter fitting. Some reported it work.

I usually bypass the heater and the prefilter by connecting the intake fuel pipe to the clear pipe that come out the prefilter.
The clear pipe blak plastic connection fit nicely into the 10mm rubber pipe and the clip from the rubber pipe is good too
Do I make sense?

The only bother is that the pipe is screwed to the rear of the heater and the only possible way to unscrew it is by removing the Air intake manifold as the screw top is right up under the manifold
Well, I never got it out without removing the intake and I did tried few times to do it with the manifold in situ and this only resulted on braking the "brittle" plastic pipe from the heater as I was applying some force... Then maybe not a good idea...

Right now I am just waiting for my tank to be totally clean then I will do it but at the moment the prefilter is still catching some crap...

Hope you get it sorted soon Those bubbles can be really annoying to find where they are coming from...

 

[runningman]

Thanks Olivier.

Will do this over the weekend, but will PTFE tape react to the diesel? I don't want it to start breaking down/dissolve over time and get into the system. Just a thought, anyway I will give it a try and fingers crossed there is no more bubbles.

Cheers

 

[Olivier]

Should be OK and anyway the main filter would pick it up.
I did it before and the tape was still OK after awhile.

 

[runningman]

Olivier.

Was you engine experiencing knocking? and did fixing the o rings cure the air trapped in the system and the knocking?

 

[Olivier]

The Engine was OK, bypassing the prefilter and the heater cleared all bubbles.

 

[runningman]

Olivier

I done what you suggested and the engine is still knocking and bubbles in lower most fuel line. Slacked off injector number 3 and knocking seemed to go away, replaced number 3 fuel delivery valve crush washer and O ring but made no difference.
No smoke from exhaust, plenty of power, starts first time but engine over runs slightly when coasting to a stop.
Could it be a fault with the pump or timing mechanism on pump sprocket.
What else could it be.