Seems like to begin with the system wasn't properly bled. I don't know what the problem is now that it runs on its own. The FSM has a spec on how much the lift pump should displace while cranking as a crude test.

Sixto
MB-less

There is a screen on the outlet tube from the fuel tank, at least on 82-85 300D's. Search for info. You need just the right socket to remove them. Even easier, try blowing air back thru the outlet tube at the engine to unclog the screen. Then, use the hand primer pump per the manual to get fuel to the spin-on filter. Also, try pumping the primer pump as you run the engine from the tank. Wouldn't hurt and might help diagnose.

No primer pump on the '87 603s. Pull the secondary (canister) filter and fill to the brim with diesel or purge.

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WARNING: this post may contain dangerous free thinking.

Try running it on a outboard engine tank, pumping the primer ball. Alternatively, use a electric fuel pump and a remote tank.

May have a air leak in the fuel line under the car at the retaining mounts.

If you pull the tank screen a 46MM or 1 13/16 socket is needed.

How much fuel in the fuel tank?

As Jim pointed out, check the air intake side for a plugged air filter or some other obstruction. Not likely given that you had it running on the diesel purge and then a temp. fuel tank under the hood, but nevertheless easy/quick to check.

Have you tried removing the vacuum line from the fuel shut-off valve to make sure you don't have a messed-up vacuum system (i.e. fault in the vacuum switch at the ignition switch)?

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

With the additional info posted by the OP, I'm going with the fuel system as the problem.

If it runs on diesel purge and on diesel when sourced from an external source, then the problem is back further....

If it runs on the external source, I'd be inclined to eliminate the pump and filters.

The primary filter (non canister) never fills up completely when running.
Here's a question, does the primary filter show any air bubbles in the fuel?

If so, you've got a leak in the line.

If the pump works on an external source, but not on the car's tank, and an air leak is not the problem, it's pretty likely you've got blockage. Tank strainer, collapsed hose, etc.

Jim

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You shouldnt have the prefilter full of air. There is usually a small bubble of air in the filter but that's it. If it's filling with air then your rubber lines at the back going into the fuel tank may be allowing air to get sucked in.

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1987 300E

So this past week I have pulled the tank and cleaned it. Put in a new tank strainer and replaced rubber lines from the tank. The strainer was pretty dirty, but not as bad as some I've seen on here. I also cleaned the metal lines with some purge and compressed air. Checked the metal lines with a mityvac to see if they're leaking and they were good. Put everything back together with a new inline filter. Started it up and same thing runs for a few seconds then dies.

Now I'm thinking the metal supply line is the issue. When I cleaned it out with compressed air it was filthy and a couple little solid black chunks came out. So I think there is either a blockage or a crushed section restrict fuel flow. One weird thing that happened is when I put fuel in the tank I was getting flow out both the supply and return hard lines. I put the supply hose on and realized I forgot the clamp when I pulled it off nothing came out of the line. I blew some low pressure air into it and the it started flowing again.

It still seems like it starts and runs with the fuel in the inline then the fuel level in the filter drops and it stalls out.

Do you think I'm headed in the right direction? What's a good way way to make sure this line is clear? Thanks again for all the help!!

Temporary jump the tank ports direct to the filter ports with rubber hose.

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sounds like a blockage in fuel supply.
"The metal supply line is the issue. When I cleaned it out with compressed air it was filthy and a couple little solid black chunks came out" assume there is a semisolid mass in the fuel line (cooties,algae fungus) physically removing the mass may be the option left to you
then treating the tank with a biocide or at least Startron to dissolve
the remainder.

Get a long enough piece of heavy duty weed wacker line and use that to ensure your lines are clear, melt one end a bit to allow the plastic to form a rounded ball rather than any sharp edge on the end and then feed that front to rear into the steel lines until it comes out the other end.

This past week I cleaned out the metal fuel line with the weed Wacker line (thanks happy happy that was a great idea). It was a little funky, but no solid mass came out. Then I decided to set up the temp tank and run another can of purge to make sure it was running and all air was bleed before hooking it back up to the tank. This time even running purge I was getting the hesitation between 1000 and 2000 rpms. Every time it's been running on purge it has smoked a lot, I thought this was just the purge burning up gunk. This time what I thought was condensation coming out of tailpipe is actually fuel. The smoke it's putting out also burns your eyes.
From doing a little research it looks like this is from bad injector/injectors or lift pump timing. Any other possibilities?
Are these things that could go bad overnight? I definitely also had a fuel supply issue because I was having the prefilter drain all the way down when it would start. Maybe running the purge dislodged some gunk that got into the injectors? The prefilter now stays completely full when I start it, but I'm still getting the same start then stall. I think my next step is to pull the injectors and have them tested. Is this the logical next step? I'm really starting to feel like a dog chasing his tail!
Thanks again for taking your time to read this and helping me out!

Well you've pretty much gotten to a point where you know it isn't a fuel supply to the IP problem because it still runs like crap when the tank and lines are out of the loop. So what is left is some other engine restriction exhaust or something mechanical/timing/control related.

It will be difficult to figure out any mechanical, timing, control issue and it would seem unlikely that something along that line would happen "overnight" as well.

You stated you removed the plug located in the exhaust manifold and there was know change, the purpose of that plug is to allow a 'back pressure" test using a gauge attached to that port, simply removing that plug would not necessarily allow enough back pressure to escape to offset a plugged cat.

I would next remove the trap oxidizer replacement pipe from the exhaust circuit, two nuts at the rear end and four at the front. Removing that takes the turbo and the rest of the exhaust out of the loop and allows the engine to run completely open exhaust. If the engine still runs crappy you know it's mechanical/timing/ control not exhaust restriction.

The fuel exiting the exhaust is hard to understand based on the engine seemingly running well when you brought it home.

I assume you've verified there is no intake air restrictions, disconnecting the crossover pipe from the turbo to the intake would eliminate that as a possible factor.

Why not contact the party that sold you the car, briefly describe the problem and see if they had the same issue and what they did to repair it? If they had a garage "fix" it, get the name/number and also call that garage. It could be they sold the car knowing there was a serious problem but had figured out a band-aid fix to get it running right so they could sell it.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

When you say it starts up and then dies - It only does this sometimes? Because you talk about getting it running, but it runs rough right?

I think you have an injector that's stuck open. Maybe some fudge got inside it and it's stuck open, so that's why you're seeing a ton of fuel in the exhaust. Just take them out and see how they spray. You need a very deep socket that is really deep inside to get them out. I've seen a few around for sale, but those sockets, at least for my car, are hard to find.

Or just take it to a certified Bosch diesel shop in your area and get them to pop test your injectors. A few hours labour. Not a big deal.

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1987 300E