fuel leak at pump/filter? on W126

[RKreutzer]

Hi everybody,
when I changed the diff. fluid this afternoon, I noticed some drops around the fuel pump. It looked like the second rubber protector had the drops. (see picture 1). When I came back from the test drive after diff. fluid was changed, it was a lot worse (see picture 2). I could even smell the gasoline when I approached the rear of the car to look under it.
I filled the tank this morning and just drove it 20 minutes at highway speed before taking picture 2.
Any ideas why it would leak that much?
I wanted to do the filter anyway. Do I need to replace all the hoses or is there some pressure problem somewhere? Could it be from a clogged fuel filter?
Your help is much appreciated.
Reinhard Kreutzer

[RKreutzer]

Here is picture Nr. 2

[RPM55]

The most common cause of leaks at the pumps are the copper crush seals on the fittings at the pumps. I suggest you get new crush seals for the fittings and the check valves on the pumps. The original seals between the check valves and the pumps are thick and tend to leak . The replacement seals will be thinner than the original seals. Be careful not to over tighten the cap nuts on the banjo fittings. I have seen many of these leak from being over tightened and deforming the banjo fittings.

[RKreutzer]

Thank you very much RPM55,
I guess I can see on picture 1 the rather thick copper seal versus the thin alu seal at the filter. It was hard to see where it leaks without removal of that plastic cover and by tomorrow the fuel will be evaporated...Is there any other way except driving to see where the fuel comes from. Will idling do it?
Thanks again for your help. I'll probably replace the rubber hoses as well as the filter with the washers.
Reinhard Kreutzer

[rudy]

it looks like your fuel pump is going south...

[tower]

Rudy

What in the picture tells you that the fuel pump is going south?

Tower

[MikeTangas]

Looking at the picture it sure looks like the crush washers on the banjo bolt have lost their seal. A new filter should come with replacement washers. In looking at the picture again, I see it is the banjo fitting at the pump, you might have to source those washers at the dealer.

Have you checked the leak with the engine running? I only ask to determine if it is a heavy drip or a spray. That might give some indication of what really is bad. Could possibly be a crack in the hard line (spray), but I think it's the crush washer.

[RKreutzer]

Hi there,
I looked at the CD last night to understand that fuel delivery system better. Can anybody tell me what the "check valve" is doing and how to tell it is bad? From RPM55's comment I understand each pump has a check valve. There is also mentioned a "leak off hose", looks like attached to the "fuel storage unit". What does that do.

It's kind of too cold to lie under the car this morning and I try to learn a bit more before I actually take a stab at it.
Thanks everybody and I also hope it is too early to declare the fuel pump the villain...I would think leaking is the opposite of "not enough fuel".

Reinhard Kreutzer

[RPM55]

Unless the fuel hoses are cracking you can probably repair the leak by just replacing the crush seals. You will need 2, 007 603 010 112 crush seals for where the check valves attach to the pumps and 6, 007 603 012 111 crush seals for the banjo fittings and the fuel filter fittings. Very rarely do you see the actual fuel pump leak.

[RKreutzer]

Thanks again Mike Tangas and RPM55,
I started the car and looked at the pump. You could see fuel immediately running down that tube from the first pump, while the rest of the metal tubing seems to stay dry. You can actually see a droplet forming on the tube on my picture nr. 2. There is no spray, just the drip at probably 1 every 10 seconds.
As per the CD, you can remove the whole assembly by blocking the fuel suction and delivery hoses with that special clamp MB has and then move the whole thing out. It doesn't seem to be attached to anything else. Is that the easiest way to change the filter and the 8 crush washers? Or is it easier to take it apart right at the car?
Thanks again for your help.
Reinhard Kreutzer

[RKreutzer]

To the benefit of anybody who might not have a CD, I thought I post a picture of the print-out I made from the fuel pump
(almost 20 year old dot matrix printer...). Hope the picture will turn out ok.
In my case, as can be seen on picture 1., the washer (9) between the check valve (32) and the banjo fitting is completely missing. I tightened it a bit and it is no longer leaking. I'll get the washers and do a "professional job" next week.
Thanks again for this great forum.
Reinhard Kreutzer