w202 95 c220 runs out of gas early
 

Hey guys,
I thought I had this nailed but I had some misinformation. I understood there to be a transfer pump that moved fuel from one side of the saddle tank to the other that died. Well when I called the dealer for the part, he couldnt help me saying there is a "sensor with pump" and a fuel pump. WEll the thing runs fine so i know its not the main fuel pump. I had taken out the fuel level senders (I assume that is what he means by sensor) from a 96 before and I never saw any pump attached to them. Is there something I am missing? Is it different from 95 to 96 and I should assume there is actually a pump built in to one of my senders?

thanks, Darren

If I recall correctly, the main pump supplies pressure to a venturi that transfers fuel over the hump.

I believe that there should be a hose between the senders from one side to the other to keep an even fuel level. Also, the senders are wired in series, so if one goes bad it might still show a half tank when it goes empty. Maybe reach your arm inside the tank with the sender removed and try to find the crossover hose.

If the fuel pressure is just slightly LOW, there won't be any returning fuel to create the suction action on the driver side venturi.

Hmm...Ok. So a little history here.

The senders have never functioned very properly. When you fill the tank, it reads empty for about 150 miles then it reads full and as you approach 425 miles or so the warning light would come on. Never a big deal. Well now it reads full when you fill it so it seems like the problem rectified itself but it was around this time that this problem started. Maybe its just coincidence or maybe there is something to this. In any event, the engine doesnt get fuel when there is still gas in the tank.

So my big question now is: The fuel transfer from side to side is purely mechanical and driven off the main fuel pump by venturi? This means the pump is weak or there is a tube broken or misplaced right?

Correct,

If the fuel pressure is too LOW & doesn't push the regulator open so that fuel can return to the driverside & create the vacuum effect to suck the fuel back into the passenger side of the tank.

Checking the pressure at the rail would be my starting point.

well $hit howdy! As I got in there to do some actual probing I figured I might as well look at the pump and therefore filter (since they are right next to eachother) and realized I cant remember the last time (if ever) changed the fuel filter. Pulled it out and drained it and tried to blow through it.. Its pretty clogged! So maybe this is all I need! Will keep you posted in about another 1/8 of a tank. I have a suspicion I will be able to run it all the way to the normal 400+ miles this time though! Thanks guys!

Well I probably spoke too soon.. I ran out of gas again at 350 miles in to the tank.

Have you checked carefully for any leaks? My wife's C280 had a tiny leak, so small it created a mist that was barely visible, in the hose going from the filter to the feed line. I had issues with the sender for a couple of weeks before finding the leak and the issues disappeared, perhaps because of what mbdoc mentioned?

I never smell gas or see drips.. besides, its not that my mileage seems to suck its that I have a half tank of gas that isn't making it Into the fuel rail. Hmmm

I found this thread using the site search. I have exactly the same problem with a 1996 C200 petrol, auto, euro spec. At about 300 miles it runs out of gas. To refill the tank takes 52 litres, while the owners manual states that the tank is 62 litres. Therefore it is leaving 10 litres (a little over 2 gallons) in the tank. Once refilled it starts and drives well. The fuel gauge is AWOL, reading randomly. Occasionally there is a very slight miss or hesitation in the engine revs.
Having searched the 'net it sounds like maybe a fuel tank filter problem? or a fuel tank "balancing" problem.
Does anybody know for sure? I have EPC for part numbers if somebody could tell me what part(s) I need.
Thanks in advance for any help. Greetings from Ireland.
Eddie.