After dealing with a lube oil leak on my 1982 300SD, I end up with a new problem that is bothering me. A week ago after drive to work and had my car parked with engine running in idle, I heard a loud knocking from somewhere from my engine. I turned it off quickly and after about five minutes I start it again and the knocking came back but in idle only. If I bring the engine at 1300 RPM the knocking will stop. Since that day I drove my car many times and I heard NO MORE knocking but it start to smoke a lot of white smoke specially when in idle and taking of after be stopped. It is a lot of smoke but again, the knocking has gone since the first time. I did couple things to try to find out the reason for this smoke: I disconnected the vent hose at the top of air cleaner because I found that was a lot of blowby but it didn't help stop smoke. Even with the vent hose disconnected the oil refill cap bounce a lot when opening it with engine running in idle. I observed fuel consumption and it looks to be normal to my car. I did not open the valve cover yet to see if there are any internal damage. The coolant is clean and maintain level. I did not check compression because I do not have that gauge.
The engine power does not seem to be lower than before. I am planning to change this engine but prior to do that I would like to see what members from this forum has to tell me about this issue. All suggestions are welcome.
Thanks.

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Nyck - TX - USA

I am not sure but would loosen each fuel hard line. One at a time on each fuel injector. Watch if the smoke goes away. If not tighten the line back up again and do the next one. The problem occuring right after knock at idle was experienced might mean an injector has developed a problem.

White smoke may be water, light blue smoke is oil.
Check both levels.

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83 SD

84 CD

White smoke is also unburned fuel on a diesel.

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84 300SD was driver,now donor for 89
89 420SEL diesel swap
84 300TD parts car,soon to scrap

You mean that there is a chance of bad fuel injector or bad injection pump?
If fuel injection is the problem, the engine should not run like misfiring?
After that knocking on my garage I put a steal piece rod, like stethoscope, to hear every fuel injector and head of the engine and could not find any abnormal noise because I use to do this kind of hearing every once a while on my engine. I just came back from my car and I found engine oil level almost in the maximum on dipstick and oil around of the exhaust pipe right bellow the flexible area. I also put back the vent pipe to air filter.
Tomorrow I will follow your suggestion and see what a happen and let you know.
Thanks for your help.

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Nyck - TX - USA

If you have an early model vacuum pump which vents into the air cleaner, a failed vacuum diaphragm will deliver crankcase oil directly into the air cleaner.

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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

To make sure that the oil was not going into the air filter through the vent from valve cover to top of the air filter, I disconnected that vent from air cleaner and drove the car for two days and the smoke still the same. Then I assumed that oil from engine is not going into the air cleaner through that way. Is there any chance of the oil be traveling through the valves and reaching the combustion chamber? As my oil level is almost on the maximum on the dipstick can interfere on it?

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Nyck - TX - USA

I understand unburned diesel fuel is black.

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83 SD

84 CD

Partially burned is black. Unburned is white.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

If you want to be sure that the problem is not in the fuel injectors or the pump and you have access to a laser thermometer, one thing you can do is start your engine, run it for a few minutes, then check the temperature at each exhaust port. If one is colder than the rest, then fuel is not burning properly in that cylinder.

In order to determine whether the problem is in the injector or the pump, switch the injector with one form a "good" cylinder and repeat the above procedure.

The early vacuum pump vent is not the same as the pcv hose from valve cover to air filter. The early vacuum pump has a separate clear or white plastic hose from the vacuum pump into the air filter.

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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

This procedure is new to me and it makes sense. Supposing that the fuel injector is bad, the engine should not have a poor performance?
In my case the engine performance is same as before but producing a not normal smoke. It's like a gasoline car with valves stuck.
I will try to check the injector following your suggestion which I liked.
Thanks

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Nyck - TX - USA

My vacuum pump does not have any hose from vacuum pump to air filter.
The only connection to the vacuum pump is a metalic line that goes from pump to brake booster. Any other idea?

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Nyck - TX - USA