300sd Injector Nailing

[usmma2013]

Hey guys,
I have a persistent nailing issue on my 1981 300SD. It occurs on multiple cylinders, at first constantly then more-so under light load, often until 10-15 minutes of driving fully warmed up. On B50 or biodiesel, said nailing disappears.

I have a fully rebuild head, #1930 injectors, timing chain, about the only thing I haven't done is IP timing. (Cam Timing is fine - new TC last year) Is it worth attempting to adjust the IP by ear? I have ordered a drip tool but it won't be here for two weeks and i hate to drive with this noise. The engine has great compression and IP timing is the only culprit left that I haven't checked. The mark on the IP is already lined up to the mark on the block as far as i can see.
As an aside but perhaps related, despite starting very quickly the idle is fairly horrid until fully warmed up and even then not stellar.

Thanks in advance!

[Desert Panther]

Modern diesel fuel isnt the same as it was when these engines were designed. After the switch to ULSD, a LOT of the older diesels started nailing. There is a product made by Liqui-Moly called "Diesel Additive" that makes a remarkable difference in the way my 4 personal diesel vehicles run, in that it ups the Cetane and lubricity of the fuel and really makes a difference that you can hear and feel. The engines idle smoother and NO nailing is present, ever. If I am low on fuel and fill the tank without adding the fuel treatment, I can tell within about 6 miles, as the nailing and knocking starts to return. This isnt as much of a problem with modern diesels that are Common Rail injected, but for these older ones it is like night and day.

There are many other diesel fuel additives that likely perform the same function. I have used Power Service, Star-tron, and a few others I cant remember. I just have been real happy with the quality of Liqui-Moly products. Your results may vary, but I would be interested to hear about your experiences with this subject of cetane & lubricity improvers.

[jabstick420]

I've also been using the LM diesel additive.

Pretty much every fill-up. I usually run the tank to almost empty. Dump a can in and fill the tank to full.

Also run the diesel purge every once in a while.

[Maxbumpo]

Poor idle and persistent nailing may be caused by either delivery valve seals or injectors. If you are sure that your injector spray patterns are all good, then you could try rebuilding the delivery valves (depending on your injection pump). Research for your IP and then decide. If your delivery valves use a copper washer as a seal, and have an o-ring, it's fairly common to rebuild the DV's every 100k miles or so. New springs are also recommended in the FSM, but most folks leave the springs alone I think.

[Diseasel300]

I'll add my bid for fuel quality as well. I recently eliminated a LOUD nailing on my SDL by doing the delivery valves. Been quiet and smooth since. Filled up with fresh fuel the other day and the car has been rough and loud since (was noisy before I even got home from the fuel change). Tossed in some white-bottle Power Service (all that anyone seems to have around here) and within a few minutes it shut right back up.

[tyl604]

I also have an '81 300SD. Have been using DieselKleen for quite a while. Happy with it.

[Diesel911]

Originally Posted by usmma2013

Hey guys,
I have a persistent nailing issue on my 1981 300SD. It occurs on multiple cylinders, at first constantly then more-so under light load, often until 10-15 minutes of driving fully warmed up. On B50 or biodiesel, said nailing disappears.

I have a fully rebuild head, #1930 injectors, timing chain, about the only thing I haven't done is IP timing. (Cam Timing is fine - new TC last year) Is it worth attempting to adjust the IP by ear? I have ordered a drip tool but it won't be here for two weeks and i hate to drive with this noise. The engine has great compression and IP timing is the only culprit left that I haven't checked. The mark on the IP is already lined up to the mark on the block as far as i can see.
As an aside but perhaps related, despite starting very quickly the idle is fairly horrid until fully warmed up and even then not stellar.

Thanks in advance!

Can you take a pic of the Timing Mark. Mine has no timing mark.


When mine nailed after 10 minutes when the engine was good an hot it turned out to be the Injector Nozzles were worn out and at the same time the original Bosch Nozzles have two tiny passages drilled in the tiny tip that get entirely plugged with Carbon.
See post #3 for a pic: Injector nozzles 300d

But, the issue could be a combination of timing, valve adjustment and Injector issues (low injector opening/pop pressure can also cause nailing).


B50 or biodiesel has a higher cetane rating so it ignites easier and is not as prone to knocking.

[usmma2013]

Thanks all! I'll have to look into the delivery seals. Would that not present itself as leakage around the top of the IP as well, or is this internal leakage which then affects the timing or pressure of fuel to the injectors?

I'll take a picture of the timing mark tonight.

I've ordered some LM Additive and I'm hopeful!

[volker407]

Originally Posted by usmma2013

Hey guys,
I have a persistent nailing issue on my 1981 300SD. It occurs on multiple cylinders, at first constantly then more-so under light load, often until 10-15 minutes of driving fully warmed up. On B50 or biodiesel, said nailing disappears.

I have a fully rebuild head, #1930 injectors, timing chain, about the only thing I haven't done is IP timing. (Cam Timing is fine - new TC last year) Is it worth attempting to adjust the IP by ear? I have ordered a drip tool but it won't be here for two weeks and i hate to drive with this noise. The engine has great compression and IP timing is the only culprit left that I haven't checked. The mark on the IP is already lined up to the mark on the block as far as i can see.
As an aside but perhaps related, despite starting very quickly the idle is fairly horrid until fully warmed up and even then not stellar.

Thanks in advance!

The B50 Biodiesel has a different behavior than normal Diesel fuel.

As the noise disappears after 10-15min it can be related to IP timing.
How old (how many miles) are the nozzles?
Does the noise go away with half or full throttle?
Is the idle knocky or uneven or both?

Fast testing:
Add 1 Liter of 2stroke oil and/or 5 liters of canola oil from a supermarket to a full fuel tank and observe / tell us what happens.

Gruß
Volker

[volker407]

Originally Posted by usmma2013

Thanks all! I'll have to look into the delivery seals. Would that not present itself as leakage around the top of the IP as well, or is this internal leakage which then affects the timing or pressure of fuel to the injectors?

I'll take a picture of the timing mark tonight.

I've ordered some LM Additive and I'm hopeful!

If you have a MW Pump on your OM617A W126 there is no O-Ring to start leaking.
In that case I would exclude the delivery valve seal. That is only relevant for M pumps which are on the OM603A SDL engines.

Gruß
Volker

[usmma2013]

The nozzles have about 3,000 miles on and around a year and a half old. They were just inspected, cleaned, and tested last week.
The noise goes away over half throttle. The idle is smooth sounding (no excessive knocking), but physically rough especially when cold and almost like the engine is having a difficult time staying running. When warm is smoother, but still shakes the car.

Originally Posted by volker407

The B50 Biodiesel has a different behavior than normal Diesel fuel.

As the noise disappears after 10-15min it can be related to IP timing.
How old (how many miles) are the nozzles?
Does the noise go away with half or full throttle?
Is the idle knocky or uneven or both?

Fast testing:
Add 1 Liter of 2stroke oil and/or 5 liters of canola oil from a supermarket to a full fuel tank and observe / tell us what happens.

Gruß
Volker

[volker407]

Originally Posted by usmma2013

The nozzles have about 3,000 miles on and around a year and a half old. They were just inspected, cleaned, and tested last week.
The noise goes away over half throttle. The idle is smooth sounding (no excessive knocking), but physically rough especially when cold and almost like the engine is having a difficult time staying running. When warm is smoother, but still shakes the car.

At first I would change the governor idle damper bolt.
Mercedes No 000 074 26 74,
35,50$ directly from Mercedes

Adjustment Bolt 0000742674 - Genuine Mercedes-Benz - 000-074-26-74 | Pelican Parts

You also need an O-Ring ID 8,0mm OD 10,0mm

It has to be a brand new idle damper bolt. If you compare the springs between the old and the new one you will know why.

And test the 2stroke oil / canola oil. That is a very cheap diagnose for further decisions.


Gruß
Volker

[usmma2013]

Volker,
I have the new style rack bolt; i installed last year when i did the timing chain.

I'll add a bit of oil tonight, curious what is that function of that/what will that tell us?
Thanks again!

[Rogviler]

Sounds like what I went through chasing the nailing on mine. It's satisfying when it's finally fixed though, so keep at it.

-Rog

[usmma2013]

What ended up being the problem with your car?

I just went out and added some DieselKleen + Cetane Boost, as well as added 5 gallons from a good fuel station down the street, just in case i got a bad/old batch of fuel.
I drove around for a bit and it didn't seem to help much, if at all.

Given that a higher cetane fuel (B50+) eliminates the nailing/chattering, would that indicate excessively advanced timing or excessively retarded timing? While the pump marks line up, I would not be surprised if the pump had been replaced or something at some point in this cars life.

Originally Posted by Rogviler

Sounds like what I went through chasing the nailing on mine. It's satisfying when it's finally fixed though, so keep at it.

-Rog