A single faulty injector.

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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.

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'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.

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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)