More Fuel Return

[Greg Hermann]

>On Tue, 20 Oct 1998, Vogt Family wrote:
>> I have read about even high pressure fuel injection systems with tank
>> return still having vapor lock problems with frame rail mounted pumps.
>> They even have pump overheating problems even though the full fuel flow
>> is running THROUGH the pump motor.  The only thing that will solve some
>> of these is going to an in the tank pump.
>
>Ummmm, i dunno about that...There are an awful lot of Fords similar
>to mine running around here with frame rail mounted pumps. We've
>had our share of hot summers since it was manufactured in '89.
>BTW--see also Volvo, Peugot, and other Bosch systems that use an
>external pump (link available on the DIY_EFI website though the
>material only hints at where the pump is actually mounted).
>
>I think this whole thread started innocently enuf as someone
>mentioned that even an in-tank pump will not be submersed when
>fuel level gets low in the tank.
>
>Please don't take this as a personal attack, I'm just trying
>to point out that you can't believe everything you read.
>Especially not here!  :)
>
OK, enough BS and mis-information!!-- I have had SEVERAL Volvos with
D-jet--both four and six cylinder. They have a frame mounted pump.
ESPECIALLY with the sixes (164's with the B-30, in line motor) you can make
them vapor lock AT WILL!! They do not have a cross flow head, and the
radiated heat from the top of the exhaust ports and exhaust manifolds COOKS
the fuel in the rails. Only simple solution is to shield and insulate the
rails AND run small coolers (about like a power steering cooler on BOTH the
supply and return lines. Anyone who wants to argue that a tank of literally
boiling hot fuel is safer then having the coolers--I'm ready!! I have heard
that Mercedes with the D-Jet injection have similar problems.

The bottom line on this is that it appears that none of the manufacturers
have too much more of a clue as to how to how to handle fuel properly than
most of the comments on this subject indicate that we do!!  It appears that
rather than hire a few engineers who know how to design systems for pumping
"difficult" (translation =  low boiling point) liquids, such as propane,
butane, anhydrous ammonia, freons, etc. (and also the water from the
condensate hot well in steam turbine power plants) the manufacturers have
collectively groped around for decades and let the general public act as
their proving grounds. (And probably jump anxiously at the excuse that less
fuel line makes it safer then doing it right!!!) (When the truth is more
like: Not only is it more expensive to build it right, but it also costs
more money to hire people who know how to design it right!!!)

Assuming anything found stock on any vehicle fuel system to be well
designed is a serious, possibly extremely dangerous and or expensive,
mistake, particularly if you are doing ANYTHING which will generate more
heat than the assumed stock operating conditions.

I have an old IH truck (10 K GVW, 4x4) whose exhaust manifolds (under load)
radiate enough heat to get the front portion of the frame rails hot enough
to SPIT when water  is splashed onto them. Before the truck got an electric
fuel pump (and a re-routed fuel line) it vapor locked. The (metal) fuel
SUCTION line (to the mechanical pump)  was clipped onto the outside of the
hot part of the frame rail with metal clips!!! GUESS WHAT!!?!!--the truck
vapor-locked regularly. Yep--I learned how hot the frame rails get by using
water to cool down the fuel line during a vapor lock episode. And, at least
IMHO, Cornbinder engineers were generally a LOT sharper than GM's or
Ford's!!

If you think that all the bubbles (really fuel vapor, not air) in the fuel
are going away and not causing trouble by the time the gas gets up to the
rails, you are likely DREAMING! I will bet that many stray episodes of
detonation are initiated when a stray vapor bubble gets into an injector
and causes a couple of lean cycles. Re-read what Bruce said about using a
bleed orifice and how it made the thing run better. Then think about it.

Don't have time right now do do more than rant. No insult, but you guys
have all been groping around the edges of this problem. No bragging, but I
DO know how to do fuel systems right, and have spent much time pondering on
how to do it, but it would take pages and pages to describe in words. And I
have not seen much more than little bits and snips of how to do it right
described in the recent thread. If enough interest exists, maybe I could do
up some sketches plus explainations and post them, but time is limited
right now. Let me know if there is serious interest in putting something
together.

Regards, Greg (Colorado P.E. #17422) (P. Eng. to the UK and Dominion types)