Fiesta fuel tank pressure / breather - Vinnie
Has anyone else had this problem. My daughters N reg petrol Fiesta gets jerky after a while and stalls fairly often when coming to a stop. Releasing the fuel filler cap produces a hiss of escaping air/gas and driving with the cap loose is perfect. It seems like a build up of tank pressure is the problem. Is there a breather or pressure relief valve anywhere that could be blocked? Can it be removed or cleared easily if so?
Any thoughts please.

Thanks to all who wrote to me regarding the wet drivers carpet in my Mondeo. I have just posted a thank you in this list but in case you can't see it was coming in through a cutout above the ECU/immobiliser. Not much rain in Somerset hence the delay in thanking you all.
Fiesta fuel tank pressure / breather - jc2
A hiss when you remove the cap is normal.
Fiesta fuel tank pressure / breather - Altea Ego
Is there a breather or pressure relief valve anywhere that could be blocked? Can it be removed or cleared easily if so?
Any thoughts please.


Yes a sligh his is normal, but a large hiss is not. I had this the wifes Fiesta. The vacuum built up so much it was hard to remove the cap. It was as you say a blocked breather system somewhere. It wasnt worth spening a huge amount of time or effort on it so I drilled a small (1/16th inch) hole in the cap.

Like all cars used to have.

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TourVanMan TM < Ex RF >
Fiesta fuel tank pressure / breather - jc2
Whic destroys the evaporative emission system.
Fiesta fuel tank pressure / breather - bell boy
im with the poster jc2, it wont be the cap look elsewhere for your problem ,first stop tps on the injection unit
Fiesta fuel tank pressure / breather - Vinnie
Thanks for replying so quick. I'm not as familiar as you and jc2 on modern cars - what is ment by destroying the emissive system and what is the tps and where do I find/check/repair it please?
Best wishes, vinnie.
Fiesta fuel tank pressure / breather - bell boy
they have what is called a closed system to prevent fumes going to atmosphere and killing ozone thingies
the tps is next to the stepper motor under the air box it looks like a large trebor mint and is either coloured black or red,these are slightly adjustable to conpensate but are basically a potentiometer and they go faulty ,have a mess and see what you find,a new one is about £20 if it needs one,or try a s/h one from the scrappy first ?
Fiesta fuel tank pressure / breather - bell boy
nearly forgot check all breather pipes are clear as well including the one to the black box on the bulkhead (map senser)
Fiesta fuel tank pressure / breather - jc2
Fumes from the tank are collected in a canister loaded with activated charcoal;this is purged when the engine is running "closed loop";ie. controlled by the HEGO(lambda) sensor.
Fiesta fuel tank pressure / breather - Civic8
>>this is purged when the engine is running

Usually at high engine revs,but as jc2 said.

I thought the tank cap had a valve built in to introduce air pressure in as vacuum got too great in tank,ie if this failed its a new petrol tank cap needed??
--
Steve
Fiesta fuel tank pressure / breather - Vinnie
Thank you to all who replied to me. I had a good look round, breather to map sensor was clear, took off tps & lubricated it with a little WD40 (couldn't do much else), cleaned around the butterfly in case dust or gunge was holding it and its bypass was clear. It still stalls so spoke to daughter and she is going to run the car with the fuel filler cap loose (and remember not to overfill the tank & tighten cap for the MOT!)
Thanks again for all your thoughts & time. Bast wishes, Vinnie.
 

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