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Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 22744
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a S350 on a 11 plate. I get a fault when the fuel just

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I have a S350 on a 11 plate. I get a fault when the fuel just drops below half. it then lacks power and won,t change gear until well over 2000 revs and when you lift off it will stay in the same gear. so it is high revving when you are slowing down. if you stop the car and turn it on again the problem goes away. It stores no faults but it does say the ECU has rebooted. This fault is very intermittent, but only happens when it has less than half a tank. Also it seems to drive so much better when above half a tank.
Can you help?
Hello I'd 1st suggest loosening the fuel filler cap to see if this helpsthere's a 1 way valve in cap to allow air into the tank but not out and so prevent a vacuum building up inside which can stall the main pumpif this helps then replace the cap
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Customer: replied 2 years ago.

Many thanks will give that a go. It doesn't seem to be pressurized when I open the cap to fill up

OKif that doesn't help, then I'd say its likely the fuel pickup on the pump inside the tank is blocked or broken so struggling when there's not a lot of fuel in the tank to help with increasing pressure at the bottom of the tank

Hi Tim

do you still need help ?

Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. so if my answers have been helpful please rate my answer.

Customer: replied 2 years ago.

I will rate you, but only time will tell if its fixed, as its such a intermittent fault. But what you've suggested was helpful. Thankyou