ML 270 (W163) Fuel pump not pulling fuel from the tank but works fine with fuel in a jar

[ants-uk]

So I've put the engine back together after a dirty job of cleaning the air intake manifold and replacing the swirl flaps etc. but then had problems trying to get the car to start.

After a lot of head scratching and testing, it was clear no fuel was getting into the system so I removed the fuel-in hose from the line and whacked it in a jar of fuel and the engine spluttered into life for the duration of the fuel in the jar. Result!

I'm assuming the fuel is sucked from the fuel tank (by the low pressure fuel pump?) rather than a fuel pump being in the back of the car pushing the fuel towards the engine. Is that correct?

If so, why isn't it pulling the fuel from the tank but is capable of sucking fuel from a jar?

Any tips would be much appreciated, thank you.

 

[Uncle Benz]

Did you remove any of the fuel lines during the work? I guess you probably did. The O rings on them tend to go hard and don’t seal very well. They let air get sucked in when the pump is trying to draw fuel from the tank. It needs a lot more suck to drag fuel up all the way from the tank, but less to pull it from a jar close to the pump. Imagine you sucking the fuel up from the jar with a straw vs trying to suck it from the jar up an eight foot straw. That’s probably why it runs out of the jar. Take another look at the O rings on the pipes is my advice.

 

[ajlsl600]

Does that system have a tea bag filter in the tank?

 

[mersum1es]

Is jar put before of after fuel filter? Sometimes there has been crack on fuel filter housing (if plastic housing system), or fuel lines been very brittle. As above o-ring leaks are common problem, perhaps now when fuel travel distance is much shorter than normally, even leaking lines are capable getting fuel to hp hp pump.

 

[oigle]

My last issue was similar and turned out to be a leaking O ring seal in the low pressure pump sandwich. They compress and go flat from age. I could'nt buy one and had to get one made.