Gas Tank Removal-71 280se

[el sea]

Checkout absolute tank cleaning in st petersburg florida. I utilize the fuel in your tanks and circulate this through my filtration unit.


Luther

[mbgingerbread]

This post reflects follow-up to gas tank removal-1971 280SE.
I have conquered the fuel system as I know it:
Removed Battery
Drained tank
Cut/Removed all old rubber hose connections
Removed sending unit and gasket
Waited a couple of days for the tank to air out-Filter at tank bottom removed and rag in opening for sending unit
Scoped ( Pro Vision ) the tank-clean, clean-no trash in the flower pot-did find the remnants of an old sending unit-the replacement unit must have been replaced with fuel in the tank-found the aluminum housing, steel washer plate as well as the plastic piece which lies underneath.
Scoped flower pot thoroughly-no trash......
Used compressed air and blew thru all lines-no obstructions
Very carefully checked the fuel outlet line in the tank and the return line in the tank
Removed fuel filter, replaced fuel filter
Renewed all rubber hose connections with fuel injection hose rubber
Removed filter at fuel pump inlet and cleaned-some trash
Checked fuel pump outlet check valve-worked ok
The fitting at the fuel pump outlet was turned to the rear-reset the position for a direct shot at the fuel line( prior had excess fuel line)
Installed Fuel Tank filter
Checked the vent lines-hard plastic lines leading from the filler neck to the canister mounted in wheel well on passenger side as well as the vacuum line leading to the engine. Reconnected all vent lines.
Made all connections to the fuel filter, the injection pump inlet and outlet and the return line fitting which has the spring loaded diaghram in it.
I think I double checked everything!!!
Re-installed battery and.....
Put 5 Gallons of gas in the tank.
Fired right up and is running fine now
To be honest I am not sure if I did what needed to be done; however, I feel pretty strong that I did a comprehensive check of the fuel delivery and return system.
Running normally.......

[Todd Miller]

Nicely done!!

[Arthur Dalton]

The problems that system has is not when the tank has enough gas to go over the top of the swirl-pot , but when there is 3-4 gallons and the gas has to enter the swirl from the intake orfice at the bottom of the swirl. The return line preessure aids in keeping the pot full , so that is the test you want to verify. You want to test flow volume when you know the swirl pot is being used , which is not the case when the tank has enough gas to be above the pot
When the gas overflows the pot, the pot scavaging action is acually not being used in the feed of gas to the pump as it's function is only when the gas volume line is below it's open top.
That is when these systems run into gas feed problems. And that is why , when one does have a feed problem, our first recommend is to add some gas to the tank to assure the pot is overflowing from the top...that eliminates screens and filter as the cause of fuel feed in the diagnosis.

[el sea]

MB Ginderbread,

Nice job and well stated.

Now that the tank has been cleaned and fresh fuel is in place, I would recommend a fuel treatment that will minimize phase separation and eliminate the water that may collect. There are products that specific to ethanol and the bio-fuels.

Again, nice job, well done.

Luther

[cth350]

This is a great thread. It ties together the mercedesshop forum, www.m-100.cc and www.sl113.org. -CTH

[mbgingerbread]

Arthur;
I should be making the next test according to your recent post here-shortly, as I will be off with about 3 gallons on the next trip......
I am a simple wrencher-documentation,first, therefore, gives me great pleasure in the steps I take and from my point of view are an answer to the "Problem". The second enjoyment is to be a part of this forum which generates the whole truth such as is stated above.
Hopefully, this is the last word in so far as this sequence of trying to diagnose the fuel system is concerned..
Thanks to all.....

[Arthur Dalton]

Very Good..
That should do it ...I only mention it b/c the fuel feed system diagnostics and working principles are completely different depending on if the system is simply gravity feeding the electric pump from tank head pressure when the level is ABOVE the swirl pot then it will be when the level is BELOW the pots open top lip.
Many are not aware of these two, completely different type feed systems on tanks that use the swirl feature.
You can have perfect fuel feed when fuel level is above the open pot, only to have a non-existant or terribly slow one when the fuel level gets below the pot rim. And that is when most of the fuel flow problems on these seem to occur the most...mainly b/c good flow then requires both return line flow and pot feed hole being clear ..whereas , when the tank is full, the feed does not have to contend with any of that..just a clean screen and enough fuel to be over the top of pot.

The main reason for these pots was so the MFI would never suffer from air in the feed line to the injection pump when the tank got low..[ specially when cornering, etc]..
By having a small tank [ pot ] within the big tank, they could use the return line flow pressure to suck fuel from the main tank into the pot by scavageing thru the small hole in the pots bottom. The swirl action of the pots design does this action, making for an always full, but small reservoir of fuel when below 4 gals. Between the return line flow and the scavenge characteristics of the pot and feed hole, the design capacity/flow of the pot volume is adequate enough to meet full engines demands. And the pots scavenge ability actually allows for the pots fuel level to maintain a higher level then the main tank when the tanks fuel level gets real low.
The '80s Ford FI cars used this same design, but they had the pot feed hole up above the return line port rather then the Benz style of below the port. That was an improvement b/c the Benz one is so low in the tank that most old tanks with sediment would always plug that small pot feed hole up..whereas the Ford one was high enough not to have that problem with bottom sediment. That is why the Benz systems have the common complaint of poor fuel feed when the tank is getting low..and why we just add fuel to get the level above the lip/rim as a diagnostics tool to verify a plugged pot fill hole/return line problem. Narrows down the diagnostics real fast.
So, as long as one also has good flow when the tank only has 2-3 gallons,
you can be assured the pot feed hole is open and the return line has good flow back to the pot.
I have seen so many pumps and other expensive componenets get changed over the years to no avail..when all that was needed was to clean out the pot feed hole with a poke of a brass rod...so this is good info to have here in the Archieves. [ my main concern]
You seem like you cleaned it up well, so I suspect you are set to go...........

[mbgingerbread]

Yes; You are correct-today I was good to go and then some. Drove till the reserve light came on then added 10 gallons. I had done so much experimenting with this and that, the old girl needed a good " German tune-up" and all systems responded nicely.
I have searched the archive here several times looking for information on one subject or another. Is there a viable index in this forum which would be more convenient than the somewhat hit or miss function of the search engine?
I guess to answer my own question there has to be considerable restraint exercised on the part of experts for one reason or another.
Thanks,
Turner

[Arthur Dalton]

Your best bet on that is to go over to the 113 Group..the 113s use many of the same systems/engine.... and they have an Indexed Tech Manual in the works.....many will be applicable to your chassis..