No, J Man, I have to do this in the wee morning WEEK END hours before the condo police wake up.

I will check under the clamps that hold the two fuel lines later. It is hard for me to work under the car at my current residence, but I doubt my fuel lines are the problem barring any rock damage that may have happened. I am going to replace the clear hose connections (at the fuel pump, the IP and the large filter) and hand pump first to see if I can get it going. Funola outlined what seem to be a good procedure for bleeding the air out of the system, and I will do that once the hand pump is replaced plus the return lines going from injector to injector to fuel filter.

Thx

I was referring to the return fuel lines that run between the injectors. NAPA line at $1.20, not $20.

BUBBLES
 

I am getting a solid stream of bubbles coming out of the overflow valve on the back of the IP and thru the clear line back to the large fuel filter. I have checked all the fittings, replaced the primer pump again and cannot find any leaks. I ran the engine for fifteen minutes, and still bubbles.


The clear fuel line on the lift pump (left side of the primer pump) is a compression fitting, no added "O" rings or anything else to seal it, CORRECT?


Haven't been able to see how that much air can continue to run through the overflow valve.


Any additional thoughts, yes or no?

It's a flare fitting, not compression. No o-rings on flare fittings.

Have you tried running out out a gallon tank of fuel in the engine compartment as if you were doing a diesel purge? If no bubbles by doing that, you have rusty pin hole leaks in the supply line under the car or a leaky short rubber supply line at the tank. If you still have bubbles with the gallon tank, you still have a leak some where letting air in.

Do you have a clear line in place of the cigar hose (return to tank). That is the best place (the only place IMO) to look for presence/ absence of bubbles.

I can see pin hole leaks, but
 

if air entered the hard lines from the rear, why don't I see bubble coming into the small primary filter?


Does it matter which end of the primary filter is higher than the other?


I have replaced all the rubber fuel hoses only 5 years ago.


I also am not seeing a reason to temporarily replacing the cigar hose with a clear line. I am getting bubbles from the overflow valve thru that clear line to the top of the secondary filter which feeds right into the cigar. If there are bubbles in the clear line, I would assume that they would be in the cigar line also.

Some people just don't want to listen. The clear hose in place of the cigar hose IS the single most useful diagnostic aid for air in fuel in a Mercedes diesel, that I have a permanent one on my 85 (look at my pic above, there's a 1/2" long clear line at the filter head before the cigar hose). That banjo bolt where the 3 lines meet has a small orifice which goes into the fuel filter. Any air that gets into the fuel system ends up in that short clear line. The clear line is what you should have installed before doing anything else. Of course you can replace parts by trial and error, one by one, till the problem is fixed.

I do listen
 

Funola, I sincerely appreciate the help you have given, but please remember that this is a blog, and not everyone is a Mercedes mechanic. One needs to sort out the good and maybe not so good or maybe the terrible.


Did you also replace the soft braided line coming off cylinder #1 with the clear line? See photo where X is planted.

I am not a mechanic but that clear line is THE most important tool to diagnose air in fuel issues from my 25 years of driving diesels. Any diesel mechanic that's any good will use that tool, unless he charges by the hour plus parts and replace them one by one by trial and error.

Yes I did replace the braided lines with polyurethane lines. They were clear when new but turned brown after a year.

NOT SO CLEAR TUBING ANY MORE
 

The polyurethane tubing likely is suffering from the heat. May I suggest clear silicone? Silicone tubing has a high temp range of 400-550f depending on the type. Low end is -30 to -40f.


Go to Aliexpress com and search "clear silicone tubing"


Starts at about 60 cents a foot to a little over a dollar, many with free shipping to your home, 1-5 meter minimums.


I would look at many of the food grade as many of these can be exceptionally smooth on the inside, up to 40 time smoother than stainless, which gives me an idea. It may be a replacement for the long stainless lines, although it would need many attachments (hose is very flexible) or a channel to support it. It would defy the corrosive salts here in the Midwest.


I will get some temporary tubing to try to get the car going.

Before getting more out of control with diagnosing your air in fuel issues, stay with what works. I have no issues with those Polyurethane return lines other than them turning brown, those lines has been on the car for 3 years now with no leaks. The other clear lines is Nylon and they've been also on the car for 3 years and they stay water clear. Is polyurethane the best? No, it is listed as fair in resistance to diesel fuel. Polyurethane eventually harden at the barbs and start to crack and leak, but my experience is that won't happen for 4 to 5 years. Those return lines should be replaced every few years as preventive maintenance anyway. I'll replace them soon. Viton and Nylon is best, Silicone is POOR! Nylon is not possible for the short return lines because it is too stiff and needs clamps, Viton tubing is usually too thin for my taste. Polyurethane is tough but only rated as fair. The factory braided lines is fine if you get quality ones. They're probably Nitrile.

My engine is so strong that it wanted to start with all four hard fuel lines loosened. BUT, I put the clear line in just as you have it.


Once I tightened all four fuel lines at the injectors, the car started right away. Even though I ran it for about 15 minutes, I was still getting bubbles coming thru the line from the overflow valve into the secondary fuel filter, and then thru the clear tubing you had me install between the secondary fuel filter and the cigar hose. All four injector lines had fuel coming out of them.


Logic tells me that air seems to be getting into the system, as opposed to just having a need to clear it out. If that is happening, it seems that there are three main culprits since they are coming out of the IP. The primer pump which I put another one in. The feed from the primary filter, which is as tight as a drum and third, the clear line on the left side of the lift pump and going to the secondary filter. Attached is a photo of the connection of this line at the lift pump. Isn't this a compression fitting, as it goes face to face, as opposed to a flare fitting having a flared end squeezed around a receiver?


Since the primer pump and fuel feed seem fine, it seems that I need to check out this connection. I don't know what else to do.

If you do not believe me that's a flare fitting, you'll have to research for yourself the difference between a flare vs a compression fitting.

Do you smell diesel in the engine compartment? Is there wetness anywhere from fuel? I think I've already asked these questions.

Take some toilet paper and go around the fittings and wipe around them. If you find any wetness, fix it till it's dry.

Yes, a flare fitting
 

as I took a closer look at the brass fitting. It is smooth on the inside edges, and should not be leaking


I have checked for leaks and see none.


The car started right up, and for a little bit, there where bubbles running from overflow to large fuel filter and thru the short clear tube you suggested installing. I had primed and opened all four injector lines and got fuel from each.


For the first time, my primary fuel filter had zero air inside, and after 5 minutes of no bubbles, the bubbles started again (same path), and the car ran roughly another ten minutes. This is getting frustrating.


After seeing the bubbles running the same path as I thought they would (back thru the cigar hose), I am not understanding how adding the clear tube helps to figure things out. I should naturally suspect the lines from the tank, BUT, with the primary fuel filter being totally filled with fuel, I am not seeing any bubbles coming thru the filter, not one.


Don't get it

That clear line is the only place to see all air that is in the system since it is the return to tank, i.e. if there is air in the secondary filter (the big one), you will see it in that short clear line and may not see it in the other lines because of the orifice on the banjo bolt mentioned earlier. WHEN YOU SEE NO MORE BUBBLES IN THE SHORT CLEAR LINE, THEN THERE IS NO MORE AIR IN THE SYSTEM!

Speaking of the secondary filter I see this in your 1st post:

"I want to spank myself. In any case, the car was running perfectly and also started instantly almost regardless of the weather. Also, the return lines coming off the tops of the injectors and are obviously leaking.


I replaced the fuel filters, but cannot quite start the car."

Assuming you've replaced the leaking return lines, maybe the act of replacing the secondary filter started your problems?

rickmay,

Your problem started when you replaced the fuel filters, that's where I would look to find your remedy.

With an 83 240D, I assume you have a "01" fuel filter head (6150920108).
Did you replace the crush washer and o-ring on the fuel filter bolt when you changed the secondary filter?

Does your primary fuel filter have bronze inserts?
This feature can prevent the filter nipples from deforming when you tighten the fuel hose clamps.

Did you replace the short fuel hoses attached to the primary fuel filter?
The hoses get dry, conform to the old primary fuel filter, and then don't seal properly on the new filter when they are re-used.

Are you using original hose clamps on your primary fuel filter hoses?
The original hose clamp bands are not very wide and the adjustment screw can bottom out.
I have wider fuel hose clamps on my setup that you can see in the second photo of the first post on my Fuel filter upgrade thread.

Many people (myself included) use 5/16 fuel hose which is slghtly oversize and can leak unless you really tighten the hose clamps so that the hose can't rotate on the fittings.
IIRC the correct metric hose size is 7mm, but 5/16 hose will work if you tighten it well.
You should not be able to rotate the hose on the fitting, even if you use a fuel line clamp (or vise grip with a rag) to grasp and twist the fuel hose.

Hope this helps.:)