I have been working on my 1983 240D for a few years, every time I started it after doing work, such as replacing fuel return lines, replacing the fuel tank screen, and cleaning the fuel tank, there was no problem starting up, as it would start in about 2 seconds no matter what was done or how long the car sat. (see video 1 Url: https://www.youtube.com/shorts/KPaEEZYF7dA )
now after changing the fuel filter(attached picture), it barely starts, if at all, coughing up black smoke from the exhaust. (video 2 url: https://www.youtube.com/shorts/youG3Uja27A)
Any ideas as to what the issue is?
Thanks for the help.

Attached Thumbnails

 

Did you fill the filter with fuel before you put it on? Or maybe you are getting air in the system somewhere. You may be able to find out where by filling up the tank and parking the car with the nose at a lower level than the rear.

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1990 300d 2.5 turbo
1995 E300d

I did not prefill the filter with fuel, but after installation I pushed the primer pump at least 50 times.

You may have to bleed the air out of the hard lines by the injectors. I would do a bit of research to see what people usually do on the w123...I have w124, and with those they are self priming, but it takes tons of cranking.

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1990 300d 2.5 turbo
1995 E300d

Remove the filter and fill it with fuel completely, confirm that the seals are good at the filter, pump the primer repeatedly. Using a jump from another car to keep the voltage high crank the 240D with the accelerator to the floor until it starts. Keep the cranking to 10 second intervals with breaks in between for a minute to let the starter cool.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Thanks for the replies. I forgot to include the fact that after the car has started up, it will start like normal quickly after shutoff. I'm not sure how long after shutoff this happens, as in this video,(https://www.youtube.com/shorts/L61ED8u2fDA), it was only about a minute between shutoff and startup.

Is the car running ok now? Does the problem reoccur after it sits? If yes I'd be looking for an air leak particularly around the fuel filter seals and the fuel primer.

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

the car runs fine once started. i just went at it again today and the same problem occurs on initial startup. here is a video showing it https://www.youtube.com/shorts/DQ1ErMR62b0
this video was taken 2 days after the initial rough start video that i posted.
if the problem is air, how does that affect starting?

Air compresses, if it is in a line when it compresses there won't be enough pressure to pop injectors open to spray fuel or if there is just enough pressure to pop the injector air will be injected instead of fuel.. Liquid/diesel won't compress so any pressure the pump makes causes the injectors to reach their popoff pressure and spray fuel.

It ran fine until the fuel filter was changed, correct?

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Two burned out glow plugs could cause this type of starting.

X2 on the glow plugs. To the OP, does ambient temp seem to affect how it starts?

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

@sugar bear, thanks. I would have thought that once it is idle if true for 10 minutes, that means the system is purged of air. How is the air getting back into the fuel lines after I shut it off?
Ambient temperature doesn’t affect startup. The first startup video I posted was done in 0 degrees F
@hercules I do not believe this problem is from glow plugs as it started immediately after I changed the fuel filter
Thanks so far for the help everyone.

Glow plugs can burn out at any given time ,no one can say when.
Review, changed fuel filter, heavy long time cranking, more than one time. Bingo!
Burned out glow plugs.

Thanks for the replies, what you said @hercules makes sense because as i understand it, the black smoke from the exhaust if due to incomplete combustion which can result from burned out glow plugs because the cylinder with the burned out glow plug is not up to operating temperature on initial start, causing incomplete combustion.
it seems that it just so happened that after i changed the fuel filter a glow plug or 2 burned out. with this being a likely case, how can i quickly test my glow plugs to find which one is burned out?

The fuel filter head bolt may not be sealing fully, allowing air incursion into the hard lines feeding the injectors.

Did you replace the o-ring and the crush washer on the large fuel filter bolt?

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022