Fuel pump questions

[James Tidwell]

At 11:02 PM 12/11/97 -1000, you wrote:
>
>
>James Tidwell wrote:
>
>> At 01:03 PM 12/10/97 -0800, you wrote:
>> >Fuel splash tends to generate large amounts of vapor that must
>> >go through the purge canister to eventually exit to the engine.  In
>> >theory this should all be accounted for by the EFI system.  In practice,
>> >you can find driveability problems associated with large amounts of
>> >purge vapors.
>> >
>> >Jim Boughton
>> >jpb01 at ibm.net
>> >
>> >----------
>> >> From: Bruce Bowling <bowling at cebaf.gov>
>> >> To: diy_efi at efi332.eng.ohio-state.edu
>> >> Subject: Re: Re[2]: Fuel pump questions
>> >> Date: Monday, December 08, 1997 5:07 PM
>> >>
>> >> >
>> >> > The return line must have a min of pressure.
>> >> > All gas tanks have a line at the bottom of the tank, for the pick-up,
>> >> > and then various others, they can be mounted all over the place.
>> >> > I beleive it was some Chry. where they had some mounted on the
sides at
>> >> > about what would be 7/8 full.  On some tanks there is a large trapped
>> >> > air bubble, all I was making the point was not to let the return
line be
>> >> > covered, if the return is sometimes covered the return line pressure
>> >> > goes up, the regulator can't bleed the pressure down, and the motor
goes
>> >> > very rich.
>> >> >   Hope that better explains it   Bruce  nacelp at bright.net
>> >> >
>> >>
>> >> I have heard that the return line must exit at the bottom of the
>> >> tank, so there is no "fuel splash". I think I got this from the
>> >> JTR book. Is this true? Does it matter?
>> >>
>> >> - Bruce
>> >>
>> >> --
>> >> -----------------------------------------------------
>> >> <<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>> >> -----------------------------------------------------
>> >>                  Bruce A. Bowling
>> >>                  Staff Scientist
>> >>    Thomas Jefferson National Accelerator Facility
>> >>     12000 Jefferson Ave - Newport News, VA 23606
>> >>                  (804) 249-7240
>> >> bowling at cebaf.gov  http://devserve.cebaf.gov/~bowling
>> >> -----------------------------------------------------
>> >> <<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
>> >> -----------------------------------------------------
>> >
>> > Question: Isn't fuel vapor pressure a function of temperature or some
>> such thing? And if that is the case, then with a closed system (as in the
>> case of a gas tank with the lid on) the vapor would reach a certain
>> pressure and remain at that pressure as long as the temp remained the same.
>> Perhaps minor variations with sloshing, but always returning to the
>> appropriate pressure for a particular tem.
>
>  Yes, except that the fuel is heated by the engine.  If the fuel cap has no
>pressure release built in, the tank can build much pressure.
>
>
> I realize that, but until pressure relief occurs the system is closed and
the temp-press relationship applies does it not? Also, in my experience
many tanks seem to be below atmospheric pressure based on the inrush of air
when removing the fuel cap.Also, some fuel vapor cannisters  act as a
relief in that they are connected directly to carb float bowls (Not FI I
know) never allowing pressure to build for whatever reason, while others
have a solenoid valve closing off the system at that point until the PCM
says open. My motorcycle gas tanks get a hell of a lot of sloshing,
especially the dirt bike variety, and they never seem to notice.
					Janes Tidwell