E300TD Diesel Knock

[230K]

Hi

When i start my E300 Turbodiesel from cold she idles fine until after approx 3 mins she starts to clatter and bang (diesel knock). What would cause this any ideas there is a very definite change in engine note after 3mins and the clackety clack begins. What is the start up sequence for these cars what changes after 3mins.

Thanks,

230K

 

[TonyVianoAmbiente]

Perhaps the engine is tight (and therefore quiet) when cold. On warming up it clatters because the engine has some wear (240k) and the clearances increase as the engine warms? Just a thought.

Alternatively, could the timing chains and/or their tensioners need replacing?

 

[230K]

Hi

There is a distinct note change ( similar to when aircon clutch engages that type of change) and it happens at exactly 3 mins from a cold start up. It is diesel knock clatter that starts after this time. Just wondering what the start up sequence is do the glowplugs stay running for 3 mins does fuel quantity change after 3mins for cold starts that type of thing.

Thanks,

230K

 

[Dieselman]

They do this in cold weather once the glowplugs go out.
At first the glowplugs keep the cylinder temperatures up so the fuel ignites evenly, after they go out there is a greater rate of temperature rise and incomplete combustion until the cylinder is under more load, thus raising the temperature.

The ECU can't alter the timing so can only alter the fuelling, however the only change as I see it is the reduced load on the alternator thus the fuelling cuts back a little to steady the idle speed. I think the reduced fuelling is causing incomplete combustion due to such a small amount of fuel being sprayed into the cold air.

If the MAF is dying is can cause this and maybe if the EGR is stickinig, but if it's Ok when hot then it probably isn't an issue.

 

[TonyVianoAmbiente]

Sorry 230K. I realise my reply was not very helpful.

Tony

 

[230K]

Hi

She stays noisy clattery from then on even when warm although only at idle. I have toyed with the idea of changing the MAF but the last time i checked it she was ok on the voltage readings just slightly lower than yours.

Have cleaned it a few times since.

http://www.mbclub.co.uk/forums/showthread.php?t=9279

Does the MAF do anything at idle??

230K

 

[Wezzel]

Wack some injector cleaner in. This usually helps prevent diesel knock as it has a cetane improver (diesel equivalent of octane but the other way 'round).

 

[Dieselman]

Does the MAF do anything at idle??

230K

I thought not as there is an idle position in the TPS which takes the wiper off the bottom of the potertiomter track.

I once had serious clanking at idle in cold weather, which I couldn't get to the bottom of but changed the MAF and never had it again.

 

[230K]

I thought not as there is an idle position in the TPS which takes the wiper off the bottom of the potertiomter track.

I once had serious clanking at idle in cold weather, which I couldn't get to the bottom of but changed the MAF and never had it again.

Dieselman, just looking over my MAF results and at idle they are way lower than your new one gave.
New MAF from Bosch agent is £120 + vat MB one is £180 + vat.

Have to think about it i reckon,

230K

 

[Ian B Walker]

How about a dribbling injector?

 

[230K]

How about a dribbling injector?

Thought about that too but would it be quiet on start up and idle nicely for the 3 mins until the glowplugs cut out if i had dribbling injectors? Surely they would dribble at all times??

Really dont know now, car goes great otherwise.

230k

 

[KLP 92]

I had the same problem on my diesel. I changed the injectors, but the problem was still there. I was told its the injector pump, but i never changed mine. I gave the car a long run to Glasgow at high speed , problem has now resolved itself!

Basically when i started the car it was fine, then a few mins later it began to clatter slightly and would continue to do so when cold. When hot after you have driven the car and put it back into Park it was fine for a minute but then would start again.

Its 100% fine now. Yours could be an injector or injector pump, try injector cleaner followed by a hard run and see how it goes.