[DML] Re: Warm Start Issue (Steve Alves)

["content22207" <brobertson@xxxxxxxxxxxx>]

Loss of resting fuel pressure is not the same thing as vapor lock.
They are two totally different problems.

Vapor lock is caused when fuel evaporates in the fuel system, and the
fuel pump is unable to pump liquid gasoline past those vapors into the
metering device. The fuel delivery system is literally "locked up" by
those vapors. The metering device runs dry, the engine starves for
fuel, and ultimately dies if running.

I'd argue that vapor lock is only an issue for exceptionally low PSI
pumps, like carbureted systems use (4-6 PSI). An 80 PSI injection pump
isn't going to have any trouble forcing liquid fuel past fuel vapors,
especially since a closed loop system like the DeLorean uses provides
somewhere for those vapors to go.

BTW: Additives such as MBTE reduce the chance of vapor lock, not
increase it. That's why they're ratcheted up in the summertime. In the
bad old days (1950's & 1960's) there were no additives other than lead
(an anti knock agent), and vapor lock was a much more common problem.
It's pretty rare now. I've only heard reports of it in rush hour traffic.

"Continuous" may not have been the best choice of words, but the
DeLorean fuel system is definitely a circulatory loop. Whatever isn't
metered out to the injectors returns to the tank. This is radically
different from carbureted systems, in which fuel only flows one way
from the tank to the carb. That's how they can vapor lock -- if the
vapors can not escape, they're stuck in line ahead of the gasoline.

BTW: The particular carb I use on my DeLorean has TWO chimneys from
the bowl (where gasoline is stored until metered into the engine). I
do not anticipate any vapor issues.

Curiosity point for those who don't know: Carburetors receive fuel
using the same methodology as toilet tanks. The fuel line is
pressurized just like a household water line, albeit at a much lower
pressure. The carburetor bowl is just like a miniature toilet tank,
with a float attached to a cutoff valve. When the bowl is full, the
float rises and shuts off reception of any more fuel. As fuel level
drops, the float drops with it, opening the valve back up for more
fuel to come in. Pretty simple.

You are correct that K-Jet uses several devices to build and hold fuel
pressure: fuel pump check valve, accumulator, primary pressure piston,
and so forth. Loss of resting pressure seems to be a much bigger
problem than inability to build primary pressure. But loss of resting 
pressure means only that. The system isn't "locked up." As soon as
primary pressure is restored, it will be back in operation. The system
isn't locked up -- it just isn't primed and ready to roll. 

Bill Robertson
#5939

>--- In dmcnews@xxxxxxxxxxxxxxx, "Steven Alves" <steve@...> wrote:
>
> You would think that would be the case but it is not. All the
Delorean forums are peppered with posts describing this problem. My
thought was it may have been something else because I just did the
water pump. I have also read that it is far more common at this time
of the year because of fuel additives. The system cannot be truly
continuous or it would never build up pressure. Something has to hold
the pressure and release the excess back to the tank. I am not as
knowledgeable as many of the others here but i think it is a sping
loaded valve in the bottom of the fuel distributer. I read that the
"O" ring going on that will also cause this problem.
> 
> Steve
> #2700 




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