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  #1  
Old 01-19-2002, 12:34 AM
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Location: Houston
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Nailing - What causes it?

On my 82 300SD, I have had a nailing problem for several years.
It used to vary in intensity, but now is louder and constant in intensity. It only seems to occur at low RPM. I don't hear it above around 1000 RPM and I don't think that engine and road noise is masking it.

I have isolated it to cylinder 3. If I loosen cylinder 3's fuel line at the injector, it goes away. When I open any other cylinder's line, it increases a tad.
I have taken it to my local MB repair shop and they concur that the problem is nailing. They say it is annoying, but will not hurt anything. I have searched the web for more info, and from the little I could find, they also say that it will do no harm.
My local MB shop has also worked on other 300's with the same problem and were not able to cure their nailing either. They have replaced injectors, moved injectors and replaced pumps. The nailing remains and is constant on one cylinder.
If I run straight Lubro Moly Diesel Purge, the noise goes away (Cetane boost?). I use RedLine 85 Plus, but it doesn't seem to make any difference.

Does anyone know what causes it and what it takes to get rid of it?

The only thing I have come up with is that is some kind of pre-ignition, but I don't understand how pre-ignition could make such a sharp sound.

Wayne

82 300SD
98 ML320

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  #2  
Old 01-19-2002, 12:43 PM
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Whayne:

"Nailing" is actually usually called injector knock. It is in fact LATE fuel ignition, not "pre-ignition" -- you can't get pre-ignition in a diesel unless you do something silly like use ether to start it, or run propane or acetylene into the intake.

There are several causes of injector knock:

Bad injector (the usual cause) -- pintle sticking open or closed, worn nozzle not giving a good spray, etc. Cured by replacing nozzle.

Low compression, causing low initial heat and poor ignition -- large cloud of fuel mist ignites all at the same time instead of buring as injected, goes "bang". Cured by fixing the cause of low compression.

Missing or broken ball pin in prechamber, or badly burned prechamber. In really serious cases, chunks can fall into the combustion chamber and ruin the piston, rod, and sleeve. Cured by replacing pre-chamber, best done with head off.

Bad seal on pressure valve holder on IP. This causes serious vibration/shaking problems at idle, too as very little fuel gets injected at low speeds. Cured by replacing the seal in the IP.

Defective IP, cured by replacing. Very uncommon.

To determine which is which:

You've already isolated one cylinder (#3), so here goes:

Low compression or a bad injector will usually also result in excess black smoke, and large amounts of white smoke on startup. If you pump the accelerator with the car out of gear, intermittant black smoke usually means a bad injector.

Bad prechamber is similar, but you can pull the offending injector and look in so see if the ball pin is in place or if the pre-chamber has eroded. Check for burned out glow plug parts in the bottom of the prechamber, too, as that can cause a similar problem.

If you have IP problems, usually only a bad pressure valve holder seal, you will have low power, vibration, injector knock, but no excess smoke. When you crack the injector line, you will have normal fuel delivery around the nut. Engine runs normally above 1500 rpm or so, has good power once wound up, and doesn't smoke excessively at speed. The quick and dirty check is to loosen the injector line at the pump then tighten the lower nut -- should be 20 ft/lbs or so. The seal is a copper washer, and if re-used can fail to seal properly.

On my 300D the pressure valve holders were so loose I could unscrew two of them by hand, no wrench! Ran badly, shook like crazy, knocked something awful on #4, with some knock on #2 and #3. I replaced the pressure valve holder seals and it doesn't knock at all at idle warm!

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #3  
Old 01-20-2002, 10:59 AM
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Peter,

Thank you very much for the information.

I have replaced the injector several times.
I have also checked and replaced the ball pin.
I have checked the precombustion chamber, but I will recheck it more throughly again. This chamber has been dirtier than the others.
I have not done anything with the seal on pressure valve holder on the IP. I will do what you suggest on this.

I have not done a pressure test on the cylinder.

I recently replaced the timing chain. Before I replaced it, it didn't take much to get black smoke during acceleration but it is much reduced now.

On the white smoke, during startup, I get a bunch, esp if I haven't driven the car for a few days. When it starts, it definely is not running on 5 cylinders. I have checked and replaced glow plugs so I am pretty sure this is not the cause. It takes normally 5 seconds to get the last cylinder (I assume it is the 3rd) running. I normally have to rev it up to 1500 RPM to get it going good.

I will work on the precombustion chamber and seals. Hopefully it is not a compression problem, IP problem or bad precombustion chamber.

It has been doing this for several years, do you see any problems in running it as it is? I mainly use it to go to work, only 6 miles, but with traffic it takes me 20 minutes to get to work and 30 minutes get home. Basically the car is sitting at idle most of the trip. I plan to replace it with a E320 in two years.

Do you have any idea why the Lubro Moly Diesel Purge gets rid of the knock? Maybe it provides enough Cetane boost to compensate for the other problems.

Thanks,
Wayne

82 300SD
98 ML320
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  #4  
Old 01-20-2002, 01:50 PM
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Whayne:

Unfortunately, you have eliminated all the standard possibilities except low compression and a leaking pressure valve seal.

I would, just for the hell of it, replace the pressure valve seal on the off chance it is bad. The seal is about 80 cents or so, and all you need is a 17mm wrench -- take the injector line for #3 completely off at both ends, then unscrew the lower "nut" at the IP -- this is the pressure valve holder. Clean carefully first, dirt in the IP is deadly!

Inside there is a spring, a little valve that the spring sits on, and a steel cylinder that is the pressure valve seat. Remove all three, being carefull not to drop the spring. Under the pressure valve seat there is a copper washer -- this is the seal. Drop the new one in, re-install all the bits, and torque to 20-22 ft/lbs twice, without unscrewing.

Re-install the injector line and see what happens.

Sadly, I suspect that compression is low on #3 -- this accounts for the white and black smoke, failure to run, etc. If the pressure valve seal eliminates the nailing, you are home free -- better combustion in #3 will usually burn off all the carbon, free up the rings, clean off the valves, etc.

Moly Diesel Purge increases the cetane rating and makes the fuel ignite better -- this will reduce or eliminate injector knock if you have marginally low compression. Won't usually make much difference with a bad seal -- didn't for me, anyway.

If you are not using significant oil (less that a quart in 1000 miles or so) or have other symptoms of worn rings, I think you have a valve problem on #3.

You did not indicate what the state of valve adjustment is on you car -- I would for sure check that, and check to make sure it doesn't change when you rotate the valve -- if so, the rotator is broken or dirty, and the valves need to be at least lapped if not ground.

I'm not too happy with the notion of driving a car with serious injector knock -- you are collecting serious carbon buildup in that cylinder, the valves will crap up, and eventually you will ruin the cylinder wall and face expensive repairs.

If nothing I've suggested fixes the problem, get a leakdown test done -- if the valves are bad, you should consider a valve job.

And, of course, there is the "Italian tuneup" -- get the thing on the freeway and stick your foot in it for an hour or so, at least 75 or 80 mph. Burns all sorts of crap out of the combustion chamber, cleans the injector, etc. Check valve clearance first. Dump a whole bottle of RedLine or Diesel Purge (12 oz) in the tank first, too. This is cheap and fun! All that idling and low speed short distance driving may have just loaded #3 up with carbon and gotten the rings stuck, valves stucking open, etc.

If you are not using synthetic oil, I would change to it next oil change, also -- you are driving that SD unde the most severe conditions I can think of!

Peter
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #5  
Old 01-20-2002, 11:24 PM
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Peter,

I will give the new seal a try. I wil post back with the results. It may be a few weeks til I get time to work on it.

I adjusted the valves recently. They only needed minor adjustment. I have not tried rotating them and will try that also.

George Murphy, one of the national tech reps for the MB Club gave a presentation at one of our local section's tech sessions about 2 years ago. He also recommended what you call an Italian tuneup. He says american's baby Benz, they are made to run hard and fast.

I did do this for a short distance once. I dropped it down a gear or two and took it up to 80, after about a mile, a huge plume of black smoke blocked my rear view. It did run better even after this short distance. Guess I need to do it again, but for a longer distance.

It doesn't use excess oil, so it make just need some cleanout. I have been using a full bottle of 85 Plus with each refill.

I have not been using Synthetic oil, but plan to start doing so. I use Mobil 1 in my ML320.

Thank you once again for the help

Wayne

82 300SD
98 ML320
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  #6  
Old 12-02-2008, 12:32 AM
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Join Date: Mar 2008
Posts: 4,642
In post #4, Psfred supplies a fix for nailing related to the copper crush washers under the DV holders.

How is this possible?

What is the true action of these washers?

Should they be changed considering age even if expected to be undisturbed?

What other IP maintenance items are often overlooked?
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Last edited by jt20; 12-02-2008 at 01:01 PM.
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  #7  
Old 12-02-2008, 01:02 PM
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Bp /edit
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  #8  
Old 12-02-2008, 04:24 PM
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The delivery valve holds pressure in the injection line so that the rising plunger in the IP instantly (well, more or less instantly) opens the injector pintle and starts injection.

If the seal for the pressure valve leaks, it will take a significant amount of lift on the plunger for the pressure in the line to get high enough to pop the injector open, so the injection will be late and incomplete. This is particularly bad at idle.

Symptoms are hard injector knock but no smoke, white or black, and rough running that goes away at higher rpm, no oil consumption or obvious valve problems.

An injector sticking open will sound much the same, but it will smoke white cold and black hot.

Replacing the seals is a quick and easy repair, but they normally don't go bad. What usually happens is that the o-ring seal on the pressure valve holder goes bad and leaks, and someone replaces them without putting new seals in or does not torque them correctly (tighten to 25 ft/lbs, loosen, tighten to 25 ft/lbs, loose, then tighten to 30 ft/lbs).

Peter
__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #9  
Old 12-02-2008, 04:35 PM
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Join Date: Mar 2008
Posts: 4,642
That is identical to what I have noticed since timing my pump and installing freshly tuned injectors. Although my idle is set very low and may be aggravating this issue, it is still noticeable.

I did not know how critical the copper washers were and the FSM mislead me to believe that they need not be changed after timing (removal of DV).

How I found out, and good info:

http://www.peachparts.com/shopforum/showthread.php?t=238618

thanks psfred
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Last edited by jt20; 12-02-2008 at 04:49 PM.
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  #10  
Old 06-08-2009, 04:01 AM
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Quote:
Originally Posted by psfred View Post
Whayne:

If you have IP problems, usually only a bad pressure valve holder seal, you will have low power, vibration, injector knock, but no excess smoke. When you crack the injector line, you will have normal fuel delivery around the nut. Engine runs normally above 1500 rpm or so, has good power once wound up, and doesn't smoke excessively at speed. The quick and dirty check is to loosen the injector line at the pump then tighten the lower nut -- should be 20 ft/lbs or so. The seal is a copper washer, and if re-used can fail to seal properly.

On my 300D the pressure valve holders were so loose I could unscrew two of them by hand, no wrench! Ran badly, shook like crazy, knocked something awful on #4, with some knock on #2 and #3. I replaced the pressure valve holder seals and it doesn't knock at all at idle warm!

Peter
This description has my name all over it, as this is exactly my problem and issues. I hope new copper will make it all happy... here is my thread relating to similar issue:
Running worse after attempted tune up
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Old 06-08-2009, 10:15 PM
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Quote:
Originally Posted by rocketboy52 View Post
This description has my name all over it, as this is exactly my problem and issues. I hope new copper will make it all happy... here is my thread relating to similar issue:
Running worse after attempted tune up
Same here! Have one valve leaking at the base after removing and replacing the line while checking out the injectors (GNARLY almost covers it). Hoping nozzles and DV washers all the way around will go a long way toward reducing her rocking and thwacking so much at idle.

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