Loud At Idle
 

1985 300TD 315,000 miles

My car runs really well. It starts instantly, has good acceleration, burns less than 1/4 quart between oil changes and has been meticulously maintained since new with all service records.
Lately the car seems unusually noisy at idle. Not any weird noises, just a louder than normal diesel running sound. As soon as you raise the idle from 750 up to 1000 rpms, its sounds like a normal running MB diesel.
Has had recent motor mounts, valve adjustments etc etc. Oil has been changed every 3000 miles since day one.
The only record I CANT find is a change of injectors. Could bad/old injectors cause a noisy idle? It is not a "nailing" sound....just louder than normal diesel "clackity-clack". Could these still be the original injectors after 315K miles? Any other ideas on this?
John

There is Timing Chain Stretch that changes the Valve and Fuel Injection pump timing.

With the exception that if the Fuel Injection Pump Timing was done after the Timing Chain Stretch that would be OK.

The Stock Injectors have tiny passages in the Pintel that can get plugged solid with Carbon.

You might or might not be able to see that if you pulled one Injector and took a look at the very tip of the Injector to see if the Tiny Hole is open or not.

Also if you pull and Injector and the metal area of the Nozzle that is exposed to combustion is burned/erroded away those Nozzles have been in the Engine a long time.

Thanks D911.....I'll pull the injectors and have a look. So, if the injectors were old and worn, would this cause a louder than normal idle that smoothes out with a small rpm increase?
I'm not worried that something is seriously wrong with the car because it runs and drives so well, but I know what it is supposed to sound like at idle and it just has TOO much of a diesel sound if you know what I'm trying to say. Has me curious about the injectors or other possible causes
Thanks
John

Like I said you can pull one Injector and get some idea about them. Below is a pic; look directly in the center of the Nozzle and you will see the tiny drilled passage. There is that one and then further up in the Pintel is a larger passage drilled acrossed the Pintel.

My own belief is that once the passages are plugged solid a Diesel Purge is not going to get the Carbon out.
In the Manual the show picking out the holes with the correct sized Music Wire in a Pin vise. In a Fuel Injection Shop they would be a canidate for the Ultrasonic Cleaning Tank.

In this pic if the Black area around the Pintel is burned away or erroded; especially if that goes all the way to the Pintel; is a sign the Injectors have been in there a long time.

It is not the only thing that can cause that. I thought I mentioned the Timing Chain Stretch effecting the Valve Timing and also there is the Fuel Injection Pump Timing.

Concerning the Fuel Injection Pump timing. The timing can cause it to nail if it is too retarded/late and also if it is too advanced.

Now that I think of it low Injector pop/opening pressures can cause nailing if it is so low as to badly effect the ability to atomize the Fuel.

What is the correct music wire size?
 

As you can see from my user name, I have access to various sizes of music wire. We stock from .029 to .049 in .001 increments. This site has saved me much money & frustration, so, if anyone needs some within that range, pm me and I'll drop a few inches in the mail to you. Taped up to avoid piercing your mail carrier, of course.

Scot

Visit your dentist and ask for some used RTC files- they're great for this and for cleaning small engine carburetors. Very high quality and they're only used once.

Answer
 

Diesel Timing Chain Links Thread
Diesel Timing Chain Thread - PeachParts Mercedes ShopForum

I suggest you consult with this member to understand the value of rolling in a NEW timing chain.

http://www.peachparts.com/shopforum/diesel-discussion/330972-1985-300cd-new-timing-chain-%3D-shocking-benefits.html

http://www.peachparts.com/shopforum/diesel-discussion/325433-1985-300td-head-gasket-repair.html


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check your motor mounts