These were very nearly my exact symptoms and it turned out to be the screen in the fuel tank. We had previously changed every fuel filter and eliminated other fuel considerations. It seemed like the crud would wash out and it would work again for a bit, then after driving a while it would happen again, until it eventually cut out altogether.
Did you happen to use a fuel system cleaner recently? That is what made all the crap inside my fuel tank loosen up in the first place, but simple age can do this too. If you do find that you have lots of fine particles then you may as well have the tank cleaned and sealed inside to get rid of the rusting that's likely happening (water in modern ethanol accelerates this).

 

Nope no cleaners used recently. Its diesel so no ethanol gas here haha. Although I have been burning a lot of crap so maybe Ill drop the tank this weekend and clean it out.

 

You don't need to drop the tank unless you're going to really give it a thorough clean and inspection, the screen should be accessible on it's own. This is for a W123 diesel but maybe your car is similar enough that it's useful:
Episode 1: Changing the Fuel Tank Strainer on a Mercedes Diesel - YouTube
and another where he describes your symptoms right from the start and shows you how to make a simple took for removal. At the 3:30 mark he explains the earlier car type screen fitment:
http://youtu.be/QCUGMZiFys0

 

^Thanks for the links man! Im just gonna pull the screen and depending, guess Ill either drop the tank or not. I havent dropped it since Ive owned the car so im kinda curious to see how bad it is inside.

 

to test , [ takes some practice ] , but if you use the prime pump handle , and pump for some time , like 20 sec , at a good clip , if the tank screen is plugged , when you reach the up stroke , the handle will want to snap back down due to the vacuum created .assuming the plastic prefilter is clean .on the other hand if the main filter is dirty , the handle will become hard to push down . when you replace the main filter , always fill it first .

 

Well pulled my filter screen out of the tank today at work...and guess what.....it was like brand new! My diesel was clean as a pin too! So I filtered it, put the screen back in and refilled the car. Drove it down the road and it started cutting out again so I picked up a primary and secondary fuel filter while on my lunch break, and changed em at work.....On the way home today she ran like a champ. Pretty sure that was the deal.

I cut the old secondary filter (canister type) in half and it was definitely full of crap. Also it was completely paper instead of the newly made metal inner and outer filters, so no telling how long its been in the car haha. Im gonna say its fixed for now! Cant wait to put some miles on her this weekend and make sure!

Thanks everyone for the info should have known it would be this simple haha.

 

Congrats on fixing your problem. It's always nice to see people post the solution so the next guy can learn from it.

 

Glad it was an easy fix. I'm not sure if it would work with diesel fuel, but on my M130 I installed a clear plastic inline fuel filter, so that visually I can inspect it every time that I open the hood.

 

Yeah thats my primary filter...secondary is the stock canister filter.

 

Could the filter be my problem? My recently purchased '68 250S ran fine, all of a sudden it lost power. Can't even get up my driveway that has slight grade. Changed the inline fuel filter (was really dirty). It starts and runs ok, but as soon as I try to move, it falls flat. It does not have a miss. Is there a screen filter in the tank?

 

Yes there should be and also should be a canister filter too on those I think. Im not 100% on thpse models though.