Ford focus 2001 a smell of petrol sometimes weak sometimes strong i have had it checked by mechanic and no leaks could it be a oxygen sensor but no lights on the dash

SOURCE: smell oil but no oil leak

this sounds like a "crankcase vent valve"issue this part typically fails in colder whether as condensed water in the oil freezes and causes the engine to seep oil from the crankcase itself valve cover oil filter housing at block,the main part is located behing throttle valve but you can see the plastic hose that attatched to the valve cover,if you were to have removed the oil cap you can notice a cream like substance which is a mixture of oil and water,this is conformation of this problem also this would cause excessive oil to be consumed.google this part to get a better idea of what it looks like and what it does as it is basically a pcv system,this should be changed as it can cause engine failure

SOURCE: 2001 318c1 1.9 petrol . serious power loss

Test o2 sensor and fuel pressure