help!!! i have a 2 leter v reg xsi and i am having problems, it seems to be building up alot of pressure in the petrol tank and when i take the cap off it hisses at me, i have had my fuel feeder pipes and vent pipes cleaned so its not that. my machanic drilled a small hole in my petrol cap to let some of the pressure out and now my petrol is glugging about in the tank it sounds like its bubbling. there is nothing in my tank as i have had it checked out. can any body help me Thanks xxxxxxxxx
Its 100% normal to have a pressurised tank on a fuel injected car! Your mechanic is an idiot. My car, which is perfectly normal, will blow the fuel cap off into my hands, depending on how i was driving it just before filling. The car only vents its fuel pressure/vapours when the engine is over a set rpm (usually around
3000) and if certain parameters are correct. It vents this through a filter and into the intake where the vapours are burned off. It cant do this if you rarely spend time above the magical rpm figure (different on each model of engine) as it would interfere with the air/fuel ratio too much at low revs and cause stalling/revving. Even so unless the pressure is excessive (read as expanding fuel tank/running rich/too high fuel pressure) its not a problem. On and EFI car (as the xsi is) the fuel is pumped up to the fuel rail. The fuel rail is mounted on the engine and tends to be hot. The combination of pumping and heating on the rail means the excess fuel that isnt used by the injectors (the pump only runs at one speed generally) returns to the tank. This means that the fuel gets hotter, vapourises and pressurises the tank.
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