Diesel knock noise? w211 220cdi

[haydar]

Hi guys

I need some help.

I've got a 220cdi w211 which has covered some 100k miles. Now when I start the car for a few seconds the engine note is perfect, but then it suddenly hardens and gets louder. It's almost as if there is a slight diesel knock.

Now over the last few months I've changed the following:-

i. New main drive pully
ii. New belt tensioner
iii. New auxiliary belt
iv. New water pump
v. New injectors
vi. New MAF
vii. New EGR valve
viii. New valve seals
ix. New turbo

I'm now kind of running out of ideas, what could be causing the problem. Once the car revs rise over about 2k rpm it all quietens down.

My question is does anyone know what could be causing the hardening of the engine note. Like I said, when the car is started for a few seconds the engine note is beautiful, but then suddenly it hardens!! Is there something that turns on at this time that can be causing this?

The cars performance is fantastic and it is noticeably quicker than other 220cdi here!!!

Here is a wav of the engine sound sound.wav

This is the car starting first thing in the morning. The was was in a large garage and I was standing over the engine with the bonnet open.

The car changes note regardless of it being hot or cold, but it sounds more prevalent was cold. The oil used in the car is mobile 1 fully synthetic.

I guess my question is that the noise changes after a few seconds of startup. What could be making that happen.

Here is a wav file of the car when it's warmed up with the bonnet closed sound2.wav

 

[Dieselman]

Have the injection timing checked. The knock is a result of rapid temperature rise in the cylinders and can be exaccerbated if the timing is advanced.
You mention that the car is quicker than most, this can also be an indicator of advanced timing.

I suspect the sudden onset is when the glow plugs switch after the post ignition stage.

 

[haydar]

Whenever I've spoken to the MB guys here they say that there is no timing adjustment for this car?? That it's all computer controlled. They've got the proper DAS diagnostic system, does this let them adjust the timing? If so do you know in which memu so that I could point them in the right direction.

Listening to the engine, did you find it abnormally noisy?

Thanks

 

[Bazzle]

Sounds the same as a Nissan and Hilux I used to own. When cold is not a good time to diagnose diesel noise.

It amaxing some of the knocks and rumbles that come from diesel engines at the best of times with no fault found.

Even fuels blended for different times of the year make more/different noises.

Bazzle

 

[fredfloggle]

I can hear the note changing - mine does that when pushed at almost exactly 3500 rpm , actually I had meant to ask why - I assumed that there must be either a dynamic timing change or some sort of resonator opening - also 220 CDI .
I wouldn't say yours sounds that sweet though - no offence !

 

[haydar]

Remember that the car in an enclosed space, cold and I was standing right over the engine. But you are right, it's not sweet.

There is definitely a diesel hard knock and not a soft knock as in other 220cdi's I've heard!!!!!

Dieselman's idea that the timing might be advanced could be something worth exploring as I've just about changed everything else. By the way, the MB diagnoistic system finds no fault with the car at all, all compression tests are spot on. Anyone know how the timing can be adjusted on this car???

Thank guys

 

[fredfloggle]

After reading your post , I stuck my head under the bonnet of mine for a cold start - after the key is turned and the engine fires , the note is perhaps a tiny bit "growly" for perhaps half a second - this can be down to loads of things at that point .
After a second or so , the engine is pretty much as it is when warm -
On some earlier diesels , there used to be a wax capsule that served to advanced the pump timing when cold to make for easier starting (in fact didn't some Vauxhalls have this as a manual control)
I don't know whether the CDi engines do anything clever like advance the pump timing when cold for easier starting , or whether a dodgy water temp sender could cause this to happen all of the time . As far as I am aware , timing is fixed - though I assume that the crank angle sensor provides a datum , though at how many points through a revolution is anyones guess .
If I keep mine at around 1700 RPM and make it hold top gear , and feather the throttle , all that can be heard with the windows open is a nice turbo whistle , and a smooth engine note , it only get an edge to it at almost exactly 3500 RPM when being pushed through the gears - not when cruising (fast) .

The only other comment I would make is that there is a possibility that your fuel quality is not what it could be - next time you are in the UK , buy some Redex Cetane improver - I used to use it on an old Perkins engine in a landrover , and it made for an alltogether much sweeter and more powerful engine - actually , I'll give it a try in my CDi as well , all fuels are NOT equal !

 

[haydar]

It's interesting your point about the timimg being advanced? Something worth looking into. I've also noticed that once the engine is warm and over 1500rpm, is seems very smooth and quiet, and yes, the turbo whistle is all I hear. It's just on idle that she seems off beat??

I'll try the redex stuff and see if that makes a difference. Any chance of you posting the engine sound of your car as a comparision?

By the way, how hot does your engine run? Mine is mostly just below half way. On a few occasions when it's been run in heavy traffic it's edged just above half way. For some reason I think it runs better at this higher temperature and the engine is quieter?? Am I just being delusional??

It's so bloody frustrating!! I mean the car doesn't give off a puff of either black or white smoke, performance is really good. It's just seems too noisy (yes I know it's a diesel but on idle it's noisy for a diesel).



Regards

 

[fredfloggle]

I'll see what I can do WRT a .wav file - I can sing a few songs as well if you think it may help . I don't know how the crank angle sensor is located , but one way initiators like this can be changed for timing without moving them laterally with respect to the timing notch is to move them further away or closer to it , this also has the same effect - is there a facility to do this ?

 

[haydar]

I'm not sure the songs will help, but you could play me the tune from the old hamlet adds .

OK, some internet search time on the crank angle sensor me thinks.

 

[haydar]

OK
Took car to MB dealer today. All the mechanics gathered around to listen to the change in the engine note after the car is started. One by one different components were disconnected, such as the glow plugs switch, EGR, MAS, etc... Yet everytime the car was started, after a few seconds the engine note would change.
Putting the car on the diagnostic machine, I was there as they ran through ever test available, compression, egr, mas, boost pressure, idle speed, etc... everything checked out!! No issues at all!
They then decided the knocking noise must be coming from the timing chain. So they dismantled the head, but the chain looked OK. However they changed the timing chain tentioner, changed the hydraulic elements (lifters), resealed the injectors, put the car back together again and no joy. The car is still making the same noise.
They however observed that the inlet manifold seemed to be extremely carbonated (which may have happened when the turbo seals had leaked) and hence could have some kind of blockage. Hence tomorrow they are going to dismantle and clean this out. I believe there are some inlet valves that also may not be working properly.
Let's see what tomorrow brings.

 

[Kompressor_Dude]

Sounds like you could've bought an SLR with all the money you've spent trying to sort this out bud!

Hope they resolve the problem for you tomorrow!

 

[haydar]

The way the tax laws are in Pakistan, an SLR would have cost a cool £800,000!!!!

In fact a 4 year old 220cdi will still cost over £40,000!!!

 

[Dieselman]

The way the tax laws are in Pakistan, an SLR would have cost a cool £800,000!!!!

In fact a 4 year old 220cdi will still cost over £40,000!!!

I can see a booming export opportunity here.


Haydar, the noise sounds like the timing is being advanced for cold start and after a short while is retarding again.
This is normal, although I'm not saying the noise is necessarily.

 

[LastMinute]

I can see a booming export opportunity here.

Not really - isn't it down to punitive import duty?

 

[Dieselman]

Not really - isn't it down to punitive import duty?

Ahhh of course.
In that case wouldn't it make exported cars cheap, similar to buying from Denmark.

 

[haydar]

The noise seems normal on start up, it's after a few seconds it changes to a knocking noise.

As for the import opportunity, unfortunately after one pays the import duty one is likely to make a loss!

 

[LastMinute]

wouldn't it make exported cars cheap

Exporting cars TO Pakistan is unattractive because of the import duty that has to be paid.
Exporting cars FROM Pakistan is unattractive because you'd be unlikely to be able to recover the import duty that has already been paid.

 

[haydar]

I can see a booming export opportunity here.


Haydar, the noise sounds like the timing is being advanced for cold start and after a short while is retarding again.
This is normal, although I'm not saying the noise is necessarily.

How about some reverse engineering. What in the engine could be making the knocking noise? The cams were checked and all seemed fine. Hydraulic lifters have been changed. The timing chain was not changed but seemed OK, although the chain tensioner was changed. The MB guys are convinced the noise is coming from the top end and not the bottom end.

 

[haydar]

Exporting cars TO Pakistan is unattractive because of the import duty that has to be paid.
Exporting cars FROM Pakistan is unattractive because you'd be unlikely to be able to recover the import duty that has already been paid.

You've been to Pakistan me thinks .