Temporarily run the car from a small fuel supply under the hood. That will eliminate or condemn the fuel pump as a problem.

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'83 300D, 126K miles.

that would only eliminate the tank and hoses, i would still be utilizing the pump.

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http://i166.photobucket.com/albums/u116/OC03/240d.jpg
Current Car:
1985 300DT 55K miles

Ran bad with the cigar hose clamped off. Concentrate getting rid of the air bubbles first. You should see them being processed through the primary fuel filter.

The pretty well static bubble in there is normal. What you do not want to see is a stream of bubbles going through that filter. Perhaps a fuel line corrosion hole or tank feed rubber hose or its fittings. That is where I would look first.

thats the issue, there are no bubbles in the primary filter only between lift pump and secondary filter

lift pump must be sucking air somewhere i cant find

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http://i166.photobucket.com/albums/u116/OC03/240d.jpg
Current Car:
1985 300DT 55K miles

It may eliminate the tank and hoses. If the car runs OK, it's the hoses. If it doesn't it's the pump or its related plumbing.

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'83 300D, 126K miles.

Where did you get the primary filter? Is it an aftermarket POS or is it a well respected supplier or OE?

I don't want to tell you how much money I spent chasing the introduction of air into the SDL...........all caused by a bad primary filter.

Those clamps on the primary won't keep out air, if the primary is providing any restriction to the fuel.

If the primary isn't the culprit, one of the fittings near the tank is the next likely choice.

Finally, if any of the steel lines are compromised, air will be drawn into the system. Look carefully along all the lines for any sign of moisture. There might not be a drip, but there will be some wetness.

FIXED
advance autoparts sucks!!!!!

they sold me 5/16 PCV hose not fuel line so it wasn't getting a good seal.
replaced it with real fuel line. then the filters they sold me
two primary filters TWO!!! sucked air. purolator # F50153.
i couldnt believe it. i actually just clamped the fuel line directly to the lift pump to diag. it.

i kept an old used primary in my tool box i got from my foreign auto parts store. [the store i buy 95% of my parts] clamped it on and all is well, no bubbles.

FYI i checked the filters with a mity vac and they held vacuum fine, so you guys know i was getting crabby there for a bit. im just glad its over with.

Thanks to all of you that posted

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http://i166.photobucket.com/albums/u116/OC03/240d.jpg
Current Car:
1985 300DT 55K miles

Glad you found the issue....many times it's just something simple. I've learned to buy my MB parts from online sites like this one...you wait a few days but at least you get the right stuff and cut down on problems like you just had.

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1985 300TDT
2013 E350 Bluetec