Or a bad batch of fuel. I would crack the injector lines 1 by one while a second person is holding the engine to the right RPM to narrow it down.

__________________
CENSORED due to not family friendly words

Narrow it down to what?

__________________
'79 240D

A single faulty injector.

__________________
CENSORED due to not family friendly words

That won't tell you that you have a faulty injector. It will tell you only that you have a misfiring cylinder. If you find one that seems to be bad, you can confirm only by putting it in another hole, or by pop testing it. If you are reasonably certain that you have a bad injector you would be wasting your time going through those steps. You may as well just pull them all and test them all, since that is the next logical step anyway. If you have one bad one, you still want to at least have the rest of them cleaned and balanced.

__________________
'79 240D

Hi folks,

Just a small update. Since I am away from my tools and garage I did what I could to try to narrow this thing down. I'm pretty sure it is either a fuel or injector issue. When the engine was cold I started it up and was able to get it to knock when revved, and this time I was able to get it to increase in frequency as the RPMs went up or decrease as they went down. It was still fairly quiet at idle.
I then drove the car gently until the temp gauge showed it was fully warmed up. Then I stopped the car in a parking lot and gently revved it in park, sure enough, it was still knocking, but not quite as loud as when cold. Then I tried running the hot engine off of another quart of vegetable oil that I bought (like I did last night). Within about a minute or two on veg oil, it quieted down and would not knock no matter how hard I tried to get it to. I let it run on the veg oil for about 5 minutes (all the time trying to get it to knock and it would not). So, I switched back to regular dino diesel and in about a minute or minute and a half I was able to get it to knock when revving off idle.
Now the common sense side of me says if it was a rod or bearing knock, not only would it sound a lot heavier, but it would not go away when warm, and definitely not go away with one type of fuel and return again with the other.

SO, I am down to bad injectors or bad fuel. Would bad injectors run fine with veg oil and cause a knock with Diesel?

Thanks so much for the help and advice so far. I do appreciate it. Once I get it home I will start work on it.

__________________
2012 Mercedes ML350 Bluetec 102K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 238K (mine)
1998 Volvo S70 T5 Turbo 211K (kids)
1994 Ford F150 4WD 246K (firewood hauler)
1983 Mercedes 300D 384K (diesel commuter)

Possibly. Some alternative fuels have a higher cetane rating that diesel fuel and ignite more easily, reducing fuel knock. I agree with your conclusion on bearing knock, they would make noise regardless of the fuel used.

__________________
'83 300D, 126K miles.

Got the car home today and had some time to work on it. Started it cold and it started knocking right away. So, I shut it off and then hooked up a jerry can with fresh diesel and ran it off of that. No change, so since the fuel was fresh and from a different station I pretty much eliminated bad fuel. Next I hooked it up to a can of Diesel purge and ran it. Within 15 seconds no more knock! I ran it for about ten minutes on the purge and it sounded great. So, I let it cool and hooked the regular fuel line back up. Started it cold again, and the knock was back, but not nearly as bad as before.

So......I pulled all the injectors, and sent them off to be re-built along with the set of Monark nozzles I had sitting on the shelf for the last couple months. I guess 270K is pretty good for the original injectors and nozzles.

More to follow once I get them back in about a week.

__________________
2012 Mercedes ML350 Bluetec 102K (hers)
2005 Corvette 55K (fun car)
2002 VW Jetta TDI 238K (mine)
1998 Volvo S70 T5 Turbo 211K (kids)
1994 Ford F150 4WD 246K (firewood hauler)
1983 Mercedes 300D 384K (diesel commuter)

Do a valve adjustment first BEFORE anything else. With the cold temperatures, and tight valves, less air enters and more black smoke, due to air/fuel mixture being rich.

Valve adjustments on the OM617 are ROUTINE maintenance, like checking the air pressure in your tires, or oil level, why wait for the flat, or low oil light to come on?

__________________
Closing the store
Benzbonz.biz on your smart phone or tablet.