Fuel Filler Caps

[Donald Whisnant]

>From: Frank Mallory <frankm at erols.com>
>Date: Tue, 11 Feb 1997 08:27:18 -0800
>Subject: Re: Fuel Filler Caps
>
>Steve wrote:
>> 
>> Hi,
>> 
>>      <snip>
>>
>> The fuel filler cap normally used with fuel injected Caterhams is
>> labelled as having a 'pressure release' facility. Is this absolutely
>> necessary in a fuel injection system? Surely the pressure in the tank
>> itself is no different to that in a carb based system? So the question
>> is :- Can I use my existing fuel filler cap - which makes not mention of
>> having pressure release?
>> 
>
>You need some kind of vent or pressure/vacuum release for your fuel
>tank; otherwise, it may collapse from atmospheric pressure as the fuel
>is used up (unless your tank contains some kind of collapsible fuel cell
>or bladder).
>
>If you have a separate vent, the type of fuel filler cap shouldn't
>matter.
>


A lot of tanks are equiped with a ventilation line (in addition to the
feed and return hose lines)...  That 3rd line typically goes to a 
canister purge tank (or charcoal box) under the hood.  A solenoid operated
by the ecm vents the output of the purge tank to the intake (which will 
pull a slight vacuum on it)...  This allows the fumes to be burnt and
actually works best with a non-vented air tight filler cap...

If your tank isn't equipped with a vent line, it might be a good addition,
as this seems to be a good method of ventilation...  Also these lines
typically have a ball-type check valve at the top of the tank so that no
back pressure can be sent into it (as would be the case with a SC or
other forced air system)...

Donald Whisnant
dewhisna at ix.netcom.com