Thread: Fuel Filter/Regulator: hose to charcoal canister; why?
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Old Jul 24, 2013 | 10:52 PM
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onehundred80
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Default Re: Fuel Filter/Regulator: hose to charcoal canister; why?
Originally Posted by boostmonkey
I am trying to understand this fuel system on the SRT6 / AMG cars.

The fuel pressure regulator is integrated into the fuel filter. I understand that. I even understand the "returnless fuel rail" and that it reduces evaporative emissions by not returning heated fuel to the tank. I don't like it, but; ok.

I do not understand why the fuel filter/regulator has a hose going from what appears to be the regulator diaphragm to the charcoal canister. It is not a boost/vacuum referenced fuel pressure regulator, right? Does anyone have data logs of fuel pressure? Is it constant relative to atmospheric pressure? The fuel pressure seems to be constant, regardless of boost or vacuum in the intake manifold. So why the hose connection? Does the ECU selectively use vacuum/boost to adjust the fuel pressure for emissions?
I think the reason is because the pressure is controlled by the spring rate, so the outer side of the diaphragm has to be at atmospheric pressure, any other pressure that side of the diaphragm would alter the fuel pressure relative to the atmospheric pressure. As there is fuel in the area the air, has to go through the filter, which is at atmospheric pressure, to lessen possible pollution by fuel fumes.
These fumes are sucked into the engine at times, how and when I do not know.
 
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