I was driving my '81 240d when I had several periods when power became very low and then recovered several times. Then the power became lower and lower and died. It restarted several times and drove a short distance then died again. Finally it died and wouldn't start again. I looked at the primary fuel filter and it had flecks of black stuff and looked clogged. I removed the filter and blew through it in the opposite direction of the fuel flow and replaced it in the line. The car started and ran normally for 3 or 4 miles to my house. I put in new primary and secondary filters and used the little hand plunger to refill the system and bleed the air. I hadn't done this for a while (like most people . I'm not driving much). It seemed like it took longer than usual to get the fuel to fill the secondary filter and air bubbles to stop coming out of the junction on top of secondary filter. In fact . the bubbles never disappeared. The car wouldn't start. I tried going through the bleeding process using the plunger several more times unsuccessfully. With the system closed, I noticed there were bubbles on the source side of the primary filter when I used the plunger and there was only a small amount of fuel getting through. I disconnected the line between the service fuel pump and the secondary filter to collect some fuel to see if it looked contaminated and it looked a little darker than usual diesel fuel. I messed with the thing to where I've almost lost track of what I did and in what order. At present, I can't draw fuel from the tank with the plunger and if I disconnect the primary filter at it's outlet and hold my thumb over the end of the rubber tube between the primary filter and the fuel pump and pump the plunger I can feel some vacuum but it seems weak. You may not believe me but, I've tried to state this problem as straight forwardly as possible. So, can anyone advise me on what's going on and what to do about it?

 

you seem to be describing fuel starvation. Some guesses are your tank strainer plugged likely from algae debris in the tank trashing everything downstream. I would drain the tank just enough to see if there is gunk. There should be a drain plug.If there is you may need to have the tank cleaned and the the strainer looked at or replaced. Not a bad job. Then there are the check valves in the IP, the primer pump etc. lots of posts on the net for this problem. Cars that aren't used are subject to all manner of "time termites."

 

Alas, you have SLIME growing in your fuel tank. This is BACTERIA that live on top of water, just below the fuel layer. The only way to clean-up the system is to start at the beginning---Drain all the fuel, remove the fuel tank, wash the tank out with alcohol--cheap rubbing alcohol or denatured either will work killing the bugs. After you have cleaned all the internal tank surfaces---remove the fuel strainer on tank outlet and clean.> REFILL the tank with only a gallon or two of clean fuel. Then remove the fuel line ahead of primary filter---then blow the line clean--flushing with clean alcohol
Change the filter. Reconnect the fuel pump and flush through the pump and then replace the secondary filter. Then loosen the fuel lines at the injectors. one at a time. Then flush through the filter, pump, and secondary filters and disconnected fuel line. one at a time with alcohol. Then blow air through the injector lines. Reattach the fuel lines, leaving one at a time loose. Prime the system with clean fuel all the way through to each injector. You SHOULD have sparkling clean fuel now sitting at the injector inlets. START THE ENGINE and pray the injectors are not plugged. Immediately add the full container of fuel line purge, following the instructions. Some call for attaching the can directly to the fuel pump inlet. You want to clean and treat the injectors right away. IF a cylinder is not firing--that injector is plugged and will have to be removed and cleaned by injector shop (+/-) $50 per injector
Good luck. This service can easily run more than $2000 at a dealer. To avoid future problems, in the winter add a pint of rubbing alcohol to the tank every month.

 

Welcome to the old Diesel owner's nightmare ! .

This is FUNGUS growing in your Diesel fuel. often mistaken for algae .

In any case, it can be difficult to remove, as mentioned the proper repair is to remove and clean the fuel tank but that's a daunting job for the average D.I.Y.'er .

If you have access to basic tools you can drain the fuel tank by removing the screen on the exit hose ~ this is an easy thing to do but no matter how you approach it you're going to get a Diesel fuel bath .

Raise up the back of the car and scrootch under neath it, you'll see on the right hand side of the trunk floor a hose sticking out of a LARGE nut looking thing ~ this is the in tank fuel debris screen, the hexagonal part is 46MM , there is an exact fit inch equivalent but in a pinch I have used a REALLY LARGE pair of water pump pliers (NE : Channel Locks) . if you disconnect the flexible fuel hose as the chassis fuel pipe using a #2 `Phillipa you can then slide a 17MM box wrench up to the end and usually turning this will undo the big 46MM screen .

Have a LARGE DRAIN PAN READY, even if you've used an old piece of hose to siphon the fuel out first .

Once you've unscrewed the in tank screen and hose assembly, it and at least one gallon of nasty old Diesel fuel will come out and you can then easily clean the screen with dish soap and a soft toothbrush .

Be 100 % certain the screen and hose are *perfectly* dry before re assembling .

Go back under the hood and look closely at the clear plastic fuel intake screen, if it's translucent it's TRASH , go buy two clear ones, Pep Boys sells the correct ones for $6 .

Install and remove the secondary, spin on fuel filter and fill it to the brim with any sort of Diesel fuel additive and re install .

Pour two gallons of fresh & clean Diesel fuel into the tank and see if the hand primer works now ~ the color of the hand primer knob determines how you operate the primer pump :

A white knob needs to be unscrewed a bunch of times then given 30 long complete strokes followed by pushing it down and turning the white plastic part until it stops turning, then you can try starting the engine .

If the primer pump has a black knob you simply push and release it at least 35 times before trying to re start the engine .

The big thing here is : you now have a LOT of air in the system so after you've pumped the primer 45 + times, stopped and rotate the engine a 1/2 turn or so then pump the hand primer 45 + MORE times, it's going to want a -lot- of cranking with your foot holding the accelerator pedal flat on the floor until not only does the engine start but you have to keep grinding away on the starter until all 4 cylinders are going and the engine is running at full tilt boogie ~ this is where most fail : they engine starts, they let off the key and accelerator and the engine dies and doesn't want to re start .

I once did *exactly* this :I primed the system and started the engine, revved it a bit and let it return to a nice smooth idle , opened the gate and backed it into the street whereupon it stalled blocking traffic and didn't want to re start....

I know this reply is long but print it out and follow it and your engine will start and run .

I've been a German car mechanic for over 50 years and doing Mercedes diesels for 35 years, I drive them daily so I l know their foibles .

If you've run the battery down cranking, charge it overnight before your next try .

Always charge at the lowest setting possible ~ 1 to 3 amperes is all it takes, batteries don't like fast charging .

The deal with priming it then cranking the engine 1/2 turn and priming it again is to get at least two cylinders ready to fire .

The secondary spin on fuel filter holds a LOT of air so it's critical to fill it before installing it .

To kill off the fungus in the tank use this product, it's the once Mercedes approves of : https://www.google.com/search?q=wher...client=gws-wiz

The product is called : BioBor and as it kills the fungus in your fuel tank, the dead fungus will begin to clog the clear plastic intake fuel screen, why I said "BUY TWO" ~ every time it fills up with coffee grounds looking crud STOP and replace it then take the clogged one home and either buy another is simply clean it in the sink using dish or other liquid soap , rinse well, blow more or less dry and stand on one end, the rest of the moisture will dry out in 24 hours or so .

In this way you don't have to re prime the fuel system ~ you simply re start the engine and motor on .

If you're not up to doing all this or removing the dirty fuel tank, look up your local " GAS TANK RENEW" franchise, they'll do the entire job and charge you $350 or so, they may not understand how to prime it and re start it but it _will_ be 100 % clean of fungus, dirt, rust or anything else you don't want in there .

As a Journeyman Mechanic I can tell you that doing it your self is the best way to go as few shops are willing to take the time necessary to do the job properly and fully ~ maybe GAS TANK RENEW because they are planning to encounter rust and so clean every tank 100 % .

Get it running and don't sweat the injectors until it's been running to weeks or so with NO CRUD IN THE CLEAR PLASTIC INTAKE SCREEN UNDER THE HOOD .

YOU can do this ! .