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Scenic 2 air in diesel lines won't start


Topic starter

Hi I have a Renault scenic 2 , it has a 1.5dci engine and I bought it new in 2005 and has 60000km on the clock, the problem is that it doesn't start with the first attempt, hot or cold, then runs fine. my mechanic changed the diesel filter but the car was still the same then he changed the priming bulb and fuel lines but it's still problematic to start, I noticed that air in the fuel pipe that goes from the priming bulb to the filter as soon as I switch the car off and when the fuel  tank is almost empty the problem disappears until I fill it up again. 

Can you please help

Thanks and regards

Maurice from Malta🇲🇹


1 Answer

The fuel is draining back into the fuel tank. Otherwise you would see a leak since the fuel has to go somewhere. That sounds like there is a check valve somewhere that prevents back flow that's not working. Renault makes a good diesel but it is 17 years old. It could also be a stuck injector but typically it will run rough.

The primer bulb is for when you run the fuel tank and injection pump dry . Then you need a manual way of getting fuel back into the injection pump since it can't pump air.

Hi, thanks for your answer, as you said the fuel must be going back to the tank, the filter has 4 connections so I suspect that fuel is flowing back to the tank via the return system and thus the filter becomes empty when I switch the engine off, probably the check valve you mentioned is located in the filter itself or in the sender unit on top of the tank. I already changed the filter twice original Renault part with no success now I will try to examine the sender unit.
Thanks again and best regards.