Paul,

I pulled this quote off a discussion group.
The last line is very pertinent.

Also here is a site with lots of in tank fuel pumps to
offer.

http://www.car-stuff.com/store/?Ntt=lexus+gs400+fuel+pump

You're probably familiar with "return-type"
fuel injection systems,
but have you worked on a "returnless" system?
Returnless systems are found on many late model cars and
trucks. The
first ones appeared back in 1993 on certain Chrysler V6 and
V8 truck
engines. By 1998, all Chrysler cars and light trucks had
them. In 1996,
Toyota introduced its first returnless system, followed by
General
Motors and Ford in 1999. Honda went "returnless"
in 2001, and today
you'll find returnless fuel injection systems on almost
all new
vehicles.
In the older return-type systems, the fuel pump delivers
more fuel to the
engine than it actually needs. The excess fuel is then
routed back to
the fuel tank through a pressure regulator and return line.
But in a
returnless system, there is no pressure regulator on the
fuel supply
rail and no return line back to the tank. The regulator is
mounted in
the fuel tank and is usually part of the fuel pump module.
A returnless fuel injection system, by comparison, manages
fuel pressure
a little differently. Instead of using a spring-loaded
vacuum diaphragm
in the regulator to change fuel delivery when throttle
opening and
intake vacuum change, the regulator in a returnless system
operates at a
constant pressure. The older return-type systems need to
vary fuel
pressure to maintain the same pressure differential across
the injectors
when intake vacuum drops. When vacuum drops, the regulator
increases
pressure to compensate. But in a returnless system, this
isn't
necessary because the line pressure is always the same.
So how does the system compensate for changes in engine
load and vacuum?
A returnless system uses the Powertrain Control Module
(PCM) to regulate
fuel delivery. A fuel pressure sensor mounted on the supply
rail allows
the PCM to monitor fuel pressure. When pressure in the
supply rail drops
as engine load or speed increase, the PCM compensates by
increasing
injector duration (on time) and/or the operating speed of
the fuel pump.
Some systems (Ford, for example), vary the fuel pump's
output by
changing the voltage supply to the fuel pump module. When
more fuel is
needed, pump speed is increased by increasing the
pulse-width (on-time)
of the pump's voltage signal (pulse-width modulation).


Doug in Japan

How does it purge air out of the system in a hot soak
situation?
How does it deal with water in the fuel?

Paul Lamar

Paul

Not sure on the first question.  Assuming the use of
injectors how does
air get in the system unless the tanks are run dry.  In
that case there
is an greater problem to worry about:)

Second question.  It doesn't. That is pilot
responsibility to sump the
tanks during preflight. Minor amounts of water mixed with
hydrocarbon
based fuel is common, if not unavoidable in any motorized
equipment.

From another site informing over the counter sales staff:

"In a Returnless fuel system, a fuel rail pressure
sensor replaces the
fuel pressure regulator, and the ECM controls the fuel pump
either
directly or indirectly through a fuel pump driver module.
Fuel pressure
is varied by the amount of voltage applied to the fuel pump
as commanded
by the ECM. This has the benefits of active fuel pressure
control, full
compatibility with On-Board Diagnostics, and no heat
transfer to the
fuel tank as the pumped fuel has a one-way ticket to the
combustion
chamber. Since the system is actively monitored by the OBD
system,
faults with returnless systems rarely go undetected. One
thing to watch
for is warranty fuel pump driver modules. In many
performance
applications, the vehicle owner may have fitted an
aftermarket high-flow
fuel pump to the vehicle in place of the OE pump that
isnB!GBt compatible
with the fuel pump driver module. If a fuel pump driver
module comes
back under warranty, double check with the customer to see
if a non-OE
style pump was installed or have the installer check the
fuel pump
current draw to prevent further problems or failures."

Doug in Japan

Air gets in a fuel injection system during heat soak
expanding the
desolved air in the fuel I think. Starting an AC fuel
injection
systems when hot has been a problem for years. When you
park your
airplane it is not always level.

I thought (I'm no expert) that the problen with hot start returnless
FI such as on the late model Cessnas I have operated was due to fuel
vaporizing in the delivery plumbing, not the presence of "air". It may
be a matter of semantics here. Sorry. There were several methods that
old hands had come up with to purge the vapor out of the lines, while
trying not to flood the engine. Sometimes ya got it right, sometimes,
ya had to give it a rest, then try again. Never had to sit more than
10 minutes from a botched hot start, 2 or 3 attempts, before I got it
running.
I don't know whether or not my aircraft had ever ingested a slug of water.
Never experienced a power loss of any kind. fuel drains in tanks, and
gascolator, always checked for water contamination, only saw it maybe a
couple times, just a few little blobs.

I have no idea how it is handled in auto applications. I have experienced
a slow/weak start in my little focus, after a long run @ 85 mph. Stopping
the car to run into a store, then restart within a few minutes of shutdown.
But it always did eventually start, maybe 7-10 seconds of cranknig tops.
Your results may vary.
C. Smith