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Old 01-08-2013, 11:27 AM
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645/333 645/333 is offline
Location: uk
Join Date: Jun 2010
Posts: 1,623
Mein Auto: BMW 640i SE Convertible
Originally Posted by Yorgi View Post
Yes, the petrol cap that you need to remove every time you fill up the car.

There is a rubber seal on this cap that dries out over time and compresses after hundreds of removals, resulting in a less-than-air-tight seal. All modern (OBDII) emission systems pressurize the fuel/petrol tank. Any loss in pressure triggers a check engine light - the assumption being if pressure is leaking from the tank so are fuel vapours into the environment.

Germans are notorious for using low silicon content plastics and rubbers because they are very environmentally conscious. They want the plastics used in cars to eventually break down once the car is retired. The problem is that the plastics start breaking down too soon, within 8 to 10 years, and you start getting all sorts of electrical connection issues and plastic hoses/tanks failing.

The Asians are not afraid to use high silicon plastics and this is one of the reasons they have greater reliability over the Germans.
Hi! Many thanks for the information, knowledge increased! If you did have a lower pressure in the tank due to the cap being faulty, how would that manifest in terms of driving the car? I appreciate a code is generated and the smell of fuel may also be an indicator, I have seen many cars with fuel stains running down from the fuel tank filler cap, indicating a less than tight seal, but would the cars ie 6 series run properly???? Would you get fuel starvation as it is not being pumped effectively?????

Always said I would go back to a 6 series
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