Hi all,

Just noticed an issue starting on my 83 300D, and I would like some advice. I have noticed a knocking/moderate hammering sound when the car is started and the motor is cold. It does not knock at idle, but only if you lightly rev it a bit or put it under load when it is cold. Also, it does not knock if you rev it more aggressively. When driving if you put it under moderate load from about 1200-1500 RPM, you can hear it knocking a bit unless you either back off on the accelerator or accelerate more aggressively. Above 1500 RPM it seems to go away.
Once the car warms up the sound pretty much goes away. On occasion you can make it knock a bit if you rev it moderately off idle, but the sound is much softer when the engine is warm. On the highway it runs fine, with no knocking, but I have noticed a tad rougher idle if you are sitting at a red light.
Oil pressure is fine at both idle and on the road, oil level is fine, and it runs and drives normally. I have noticed that the exhaust has more black smoke than it used to, especially in the cold weather. The injectors as far as I know are original and have about 270K on them. I plan to have them done in the near future. It is also due for a valve adjustment and oil change in about 1500 miles.
So…What do you think, injector knock due to worn injectors, or something more sinister.
I have described it as best as I can, and I am not able to post a sound clip or video right now as I am on the road for work for the next couple days.
Thanks in advance for any advice/help

Glenn

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Cracking a line (with engine running and making the knocking noise) on each injector in turn will help to rule them out

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

I will do that once I get a chance. My main thought is since it only does it when cold and/or under moderate load, and does NOT do it at idle and not much at all once warmed up, it isn't anything real serious like a rod or bearing knock. I guess I am looking for advice on how serious it sounds based on my description. I plan on looking into it as soon as I can just the same. I suppose it could even be just a bad batch of fuel but I kind of doubt it.

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

A leaking injector can become pretty serious if not addressed quickly.

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CENSORED due to not family friendly words

There was a pic on one of the Forums of a Prchamber that had a hole cut into it from an Injector that was spraying to the side.

Someone had the Prechamber Ball Pin come loose and go to the bottom of the Prechamber and the tip of the Prechamber blew off of and the when the Piston came up they were trapped between the Cylinder Head and the Piston Head; damage resulted.

Use your best judgement.

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84 300D, 82 Volvo 244Gl Diesel

Ok, here is the latest,

Tonight when I drove it around I did a bit of an Italian tune up. It helped some but still have the knock, but only at about 1200-1500 RPM under light to moderate load. After driving about 25 miles (so the motor was definitely warmed up) I pulled into a small empty parking lot and played with it a bit. At idle in park or drive it is fairly smooth and quiet, but if I lightly increase the throttle to about 1200 rpm it will start to knock. It will knock between 1200 and 1500 RPM and if you hold the RPM steady it will knock as long as you are in the 1200-1500 RPM range. Once you go above 1500 RPM the knock stops. If you increase the load on it, it will stop knocking as well.

Now for the interesting part. I had a bottle of Diesel Kleen as well as some fuel hose and another empty jug. Sooooo, I quickly disconnected the fuel lines and ran the fuel feed and the return into a jug with Diesel Kleen in it. When I ran it on straight Diesel Kleen, no knock (or if it did knock it was so quiet I could not hear it clearly). Next I bought a quart bottle of pure vegetable oil and tried running it off of that. Same result, little or no knock if ran on straight vegetable oil Finally, I hooked the lines back up to the diesel fuel supply, and within a minute or so it started to have the knock again at the 1200-1500 rpm range.

My thoughts are this. If it was something major (rod bearing, crank bearing wrist pin, etc...) it would do it at all RPM ranges and on all types of fuel. Since it only seems to do it on straight diesel fuel I either have some bad fuel, or an injector or two that are getting weak. Still not sure why it only does it in the narrow RPM range and will not do it at idle or under a heavy load.

Again, any thoughts? I need to drive the car for the next week to ten days, a total of about 650 mile or so.

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2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

I think you need to narrow it down to one or more injectors

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

I would not expect continated Fuel to damage Main, Rod or Piston Pin Bearings.
The exception would be if the Cylinder got flooded with liquid Fuel and a hydraulic lock developed mixing Gasoline with Diesel Fuel should not cause that.

Diesel Kleen even when mixed with Disel Fuel claims to raise the Cetane rating and that tends to decrease the sound of the typical Diesel Knock.

You might want to look up what causes the Diesel Knock on the internet.
Abnoral Diesl Knock/Nailing happens when the Fuel is burning at the wrong time/stage and in the wrong place in the Combustion/Pre-combustion Chamber.

2 of the causes of that can be poor spray pattern and poor atomization of the Fuel. This is why I targeted the Injector Nozzles in my best guess since they are the tinyest parts of Metal exposed to the heat.

You also have to remember as you increase the Engine Speed the Timer advances when the Fuel is Injected. The advance in the time of injection is one of the reasons the knocking is different at different rpms.

One thing about abnormal knocking is you should not hear it after the Engine is up to operating temp.
It is typical for worn out Injectors to have an abnormal knock right after starting but once the Engine warms up to operating temp and the Ball Pin inside of the Pre-chamber is nice and hot the knocking usually goes away. The exception might be if it is really cold like freezing or below.

So to Me having an abnormal knock after the Engine is up to temp is not good.

Detonation in the Pre-combustion Chamber might also cause cracked Piston Rings. But, I have not witnessed that happening.

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84 300D, 82 Volvo 244Gl Diesel

I think the OP is in some partial denial that that anything was damaged; seems relucatant to accept that.

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84 300D, 82 Volvo 244Gl Diesel

Here is some advice to the OP. If other members on this forum, in particular those with a lot of experience, take the time to reply to you and tell you, as a first step, to crack the injector lines to isolate if it is an injector problem, its a really good idea to follow the advice before you make any other move.

Going on an "Italian tune up" run... not so much. That is what you do if you have demonstrable evidence that the problem is a sticky injector. Not when you are still asking if its a mechanical issue.

BTW where did you ascertain hat Diesel Kleen is formulated to be run as a sole fuel source? I have a bottle in my trunk and it specifies a very low mixing ratio to diesel fuel.

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

valve adjustment....

have injectors rebuilt..

r&r injectors along with new filters....

report back to us.....

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Folks,

Let me say, I appreciate the advice and suggestions. If I didn't I would not have asked in the first place. I also want to say that I am not in denial about something being damaged/worn out. Abnormal noises are never a sign that everything is just fine and dandy.

If you look back at my second post, I replied to Stretch saying that I WILL crack the injector lines as soon as I get a chance. What I forgot to mention is that I am not at home right now (out of town on a work related trip) with limited space, time, and tools to tear into the car. That is why I tried some quick and easy things to do (Italian tune-up, Diesel Kleen and Veg Oil as sole fuel) to try and see if the issue changes and possibly narrow down the problem. I was then reporting my findings so those who are helping me had the same info I had. I too am leaning toward injectors as the issue since the noise only occurs at a certain RPM range and gets softer/goes away when warm or if a different type of fuel.

I'll be home on Tuesday and will be able to tear into it then, and yes, I'll report back what I find

__________________
2012 Mercedes ML350 Bluetec 91K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 231K (mine)
1998 Volvo S70 T5 Turbo 196K (kids)
1994 Ford F150 4WD 249K (firewood hauler)
1983 Mercedes 300D 376K (diesel commuter)

Sorry your between that "Rock and a hard Place" on this one.

Different Car but over 1 Month ago I had My Belt break due to the Alternator siezing and sat on a Bridge in Heavy Traffice as My Coolant temp climed. It was near My House so I drove it home. That was actually bad idea but sometimes We make those choices.
The Coolant was boiling as I pulled into the Driveway.

Fixed now the Engine so far has shown no sign of damage from overheating but.

Now that I look back on it it since I was close to Home; once off of the bridge it would have been safer had pulled over, walked home and called the Auto Club for a tow.

Note: The third case I know of where someone pumped Gasoline into the Tank they realized they had done that and dumped 4 quarts of ATF into the Tank and drove 2 miles to our Shop.
We drained the Tank and and checked His Injectors and they are OK.

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84 300D, 82 Volvo 244Gl Diesel

Everything that OP has described points to injectors. Merely cracking lines to isolate a cylinder without moving suspect injector(s) to a different position, as everyone knows, is not conclusive evidence of a bad injector, and is basically a waste of time. At this point, doing the full test and shuffling injectors around would do little more than provide the extra 10% of confirmation.

The only way to know if you have a nozzle that is pissing is to pop test it, and that is the condition that demands swift action to prevent damage. So get those injectors out and into the shop for testing and servicing ASAP! Do the valve adjustment while you wait for your injectors. Change the fuel filters too, after running off of straight Diesel Kleen and corn oil. If you must go a few hundred miles before you can do the service, then don't worry about it-- but don't put it off beyond what is absolutely necessary.

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'79 240D

The fact that the noise goes away on different fuels suggests to me that it's something related to fuel. I'm going with the injectors.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13