4 x 4 Fuel Injection

[Michael Selig]

I am new to this list.  I am an owner of a 350 gas Hummer for the last 3
years.  Many on the Hummer mailing list have been talking about putting in a
Whipple -worm type superchargers.  I make claims that there have been
reports that the whipple is associated with bottom end going,  even with 4
bolts mains blazer engines.   Some of the problems with Off road and Fording
vehicles--are there watertigtness.  I still state that EFI is the way to go.
More low end smooth torque.  I have been waiting for this current Throttle
body injection engine to have problem, but it is hanging in there without a
whimper or a miss.   This is a post I made this week, based on several
references I have come across.  I know I have a long way to go..

----- Original Message -----
From: Michael Selig <mbs at itw.com>
To: <hml at mailinglists.org>
Sent: Monday, April 12, 1999 10:42 PM
Subject: Electronic Multiport Fuel Injection-operations 2-- long winded
alert-


For those of you gassers who may be interested in these fuel
injection systems, they are complex but really do
increase gas mileage, throttle response, Hp about 20-40, and
torque mostly at low rpms.

I have now read 1 book and several articles on fuel injection and am getting
a little more familiar with the concepts and hardware.  I revised this
twice --now it may provide some useful info.  Most of the sensors and setup
are also present on turbo diesel vehicles, so heads up.

BACKGROUND DESCRIPTION:
Fuel Injection differs from Carburetors,  in that the fuel is pressurized
before it enters the intake tract as opposed to being siphoned through a
carburetor with engine vacuum.

Early Mechanical systems were simply Nozzles and their primary function was
to atomize the fuel as it was sprayed.  The specific amount of fuel
delivered was determined by the injector pump which housed a piston for
every injector.  The displacement of the piston determined the amount of
fuel to be pumped.  The piston also pressurized the fuel.   The pump had to
be accurately, mechanically timed to the engine, like the distributor and
camshaft.

Mechanical injection systems offered several significant advantages over
carburetors, but were plagued by their lack of adaptability as well as
expensive production and maintenance costs.
Electronic injection although seemingly complex, is simpler in many ways.

There are 2 main physical types --Throttle body injection and Multiport.  In
throttle body, the injectors are placed inside the throttle body housing
above the throttle plates.  These systems look like regular carbureted
engines, and utilize wet manifolds.  Wet manifolds carries air and fuel, are
more restrictive because the runners most carry the mixture that falls out
of suspension and collects on the runner floor.  A dry manifold carries only
air.  The runners can be tailored for operating range of the engine.

Multiport injection systems (MPI) have one injector per cylinder (some have
2)  placed at the end of each runner of a dry intake manifold.  Injectors
are mounted 70-100 mm from the intake valve seat and spray atomized fuel at
the back side of the intake valve.  MPI systems still use a throttle body
with specific sized bore, not unlike a carburetor, but monitor only air.

The Injectors are specifically sized NOZZLES, but also valve actuated by
built in electric solenoids.  The electronic Control Module (ECU) determines
when each injector opens and for how long.

Fuel is provided to all the injectors by a common fuel RAIL, which is
pressurized by an electric fuel pump usually located in the fuel tank.  High
fuel pressure causes atomization of the fuel as it comes out of the nozzles.
These systems operate at standard psi and use vacuum.  Modulated pressure
regulators reduce rail pressure at times ie the amount of fuel delivered at
idle.  The regulator bleeds off excess fuel pressure back to the tank via a
return line.
Engines using forced induction are setup to provide  additional fuel under
BOOST.  As a rule,  every 1 psi of boost requires an additional 1 psi if
fuel pressure.

The injectors are sized according to their rate of flow, rather than
measured in physical dimensions of spray mechanism.  The rate is usually
calculated by the amount of fuel that the injector passes in a given time.
Aftermarket units use fuel/hour.  OEM use a more precise standard- grams or
cubic centimeters /second.

The size of the injector, pressure and volume of fuel feeding it, are fixed
characteristics that effect fuel delivery--the variable is the opening and
closing of the injectors.

The event that occurs each time an injector opens and closes is called a
DUTY CYCLE or a PULSE.  The length of time the injector stays open
determines the PULSE WIDTH.  The longer the pulse width, the more fuel being
sprayed.  During normal cruise--1 pulse/ firing cylinder.  Rapid opening of
the throttle-leads to multiple injector pulses per ignition signal.  This
provides the same enrichment function as the accelerator pump in a
carburetor.

PULSING is controlled by the Electronic control unit or computer.  Raw data
is processed and compared to data that has been programmed by the
manufacturer, but the unit can  also learn about operational or driver
patterns of a specific vehicle.  The ECU adjusts engine management via
Activators..

These systems also come in 2 varieties--SEQUENTIAL vs BATCH Firing.
Sequential--fires one injector at a time in a the sequence of the firing
order.  This offers better performance and fuel economy --but needs more
precise controls.

BATCH firing--triggers multiple injectors at a time, sometimes according to
cylinder bank-as in our gas engines.  Injectors open to 1/2 of the
programmed
pulse width and fire more than one pulse/cylinder/cycle.  Therefore only a
portion of the total fuel is injected and has to wait for the second half to
be delivered, when the intake valve opens.

The stock GM Throttle body computer pairs injection pulses.  The
ideal system sequences the injection pulses individually.


There are 2 basic control types--
MAF---MASS AIR FLOW sensed, before 1990 GM and after the
SPEED DENSITY SYSTEM.
These systems give optimal fuel mixture at all RPMs and have
made gas engines very reliable.

They involve the Electronic Control Unit (ECU) with a
Programmable Read Only Memory (PROM -our favorite) and multiple sensors.
These modules are mapped units and sense changes in
hardware --lower resistance filters, less exhaust resistance, camshaft
changes, ie and adjust accordingly.  These units have learning capability
and also
adjust to gas octane variability, air temp and driving mode (floored).

The systems have many sensors, but have been found to be extremely reliable
over many years:

Mass Air Flow Sensor-MAF--Located in the air intake and measures air flow
before reaching the engine.  It measures air volume to the cylinder by
monitoring the electrical resistance in a thin heated wire as it
is cooled by incoming air.  The more air that passes though the sensor the
more voltage is required to heat it up.  This sensor is less affected by
engine mods.

Air Change Temp sensor.  Usually located in the duct from the air cleaner
or in the intake manifold.  Measure temp of incoming air.  Used in
conjunction with the TPS. MAP/MAF to determine volumetric efficiency.

Idle air control (IAC)-Adjusts idle speed to engine load and
temp.  Threads into the housing below air intake.  Coolant is routed through
the IAC housing to enhance cold run operation.

Throttle position switch (TPS)- Tells the ECM amount and speed at
which the throttle is being opened or closed.  Measures angle of throttle
plates and how much throttle the operator is using.  Calculates Air/fuel
mixture needed during acceleration. Stock 0.54 volts. located on the
passenger side.

Knock Sensor-Works like a microphone to hear knock or pings
and retards timing..  Is imperative.  Must be installed in tge lower portion
of the block.  It must correspond with the MAP orMAF.  Safeguards against
poor quality gas.

Engine coolant temp sensor- Usually threaded into the coolant passage of the
intake manifold.  Data is used to determine cold start or warm up
enrichment, idle speed control, spark advance and Air/Fuel mixture.

Oil pressure sensor--Cuts fuel in event of oil loss.  Acts as a backup if
the relay fails.  After cranking for 5 seconds with a fail pump relay, the
oil sender will detect oil and trigger the pump.

Vehicle speed sensor--VVS --The ECU for most factory units use its input.
Aftermarket unit eliminate the VSS hookup.  The EFI will operate more
efficiently ans smoothly with it.  Most EFI vehicles use this for the
electronic speedometer, eliminating the cable drive.
===

The SPEED DENSITY SYSTEMS are basically the same as the Mass
Air Flow sensed but without the MAF and uses a Manifold
absolute sensor (MAP) instead.

Later systems use a MAP-manifold absolute pressure sensor.  This one is
cheaper, simpler, requires only a vacuum connection in addition to a harness
connection.  Factory systems mount the sensor to the intake manifold and
reads manifold pressure.  These vehicles need to be reprogrammed if
modified.

Manifold air temp sensor (MAT)-Sends air temp data to ECM.
The MAP--functions like an electronic vacuum gauge--does not
change A/F mixture.

O2 sensor-Required. Measures O2 in rhe system and converts date to voltage
which keeps incoming mixture at STOICHIOMETRIC or chemically ideal Air/Fuel
mixture of around 14.7:1.

Be they carbureted or injected, engines need to run at specific metered air
fuel mixtures.  This value changes with rpm and load.  Lean or Rich has been
used.  Lean -too much air.  Rich --too much fuel.
Air fuel has been stated in N parts of air to a constant 1 part of fuel.
Contemporary theory dictates the ideal is 14:1 for catalytic converter
operation.  Peak horsepower is attained at 13:1 ratio, but Max torque at
12.9:1 at wide open throttle.  16.7:1 is best for fuel economy and a sharp
rise in emissions, rendering a catalytic converter ineffective.  12:1 is too
rich to produce adequate horsepower and causes converter meltdown, due to
inability to burn unused fuel.  Excess fuel or too rich also washes oil from
the cylinder walls--increasing ring and bore wear.
Too lean-leads to cataclysmic event.  O2 burns at extremely high temps.
Higher combustion temps can lead to pre-ignition which can blow head gaskets
and melt pistons.

MODES:
There is a Limp home mode--in case of major system malfunction.
a OPEN LOOP mode-when not under control of the O2 sensor or
during warm up or wide open operation. Air fuel is adjusted according to the
TPS, engine rpm and other data.
CLOSED LOOP-When up to temp, wide open, and gives good gas
mileage.

GM unit notes:

There have been many variations from 1985 to now,  so there is a problem
with
compatibility of parts.

The angle of the bolt holes in the intake manifolds vary if you are
considering picking up parts a yard.  85-86 manifolds angles same as rest,
bolt to older engines.  87-92 center hole drilled at unique angle.

Always get complete setup -- sensors, harness, computer, fuel pump and
manifold from the same donor car.
There are conflicts with Beltdrive accessories, exhaust plumbing, air
cleaner.
Stand alone wiring harnesses are available.

Injectors for the 305 rated at 19 lbs/hour
For 350 22 lbs/hour.
If using small units and adapting to a 350. install adjustable fuel pressure
regular in place if stock.  Need higher pressure for smaller injectors.

Fuel Lines:
Need to be plumbed for High pressure operation--uses flare nut fittings.
Need a low pressure return line that should be at least 2/3 tge size of the
feed.  A vent tube is also needed.
Corvette  fuel lines on the passenger side,  F cars on drivers side.

FUEL RAILS:
Lines that distribute fuel to all the injectors.
Fed by incoming fuel lines, pressurized by the fuel pump and pressure
adjusted by the regulator via the Manifold vacuum signal.
Connected also to the return line.

Fuel pump:
Most TPI systems use a min fuel pressure of 40-45 psi, so an electric fuel
pump is necessary.
Factory pumps are in the fuel tanks.  OE tanks have problematic baffling to
keep fuel from running away from the sump, during low fuel cornering.  If
the pump runs dry, the engine stumbles and stalls.
The fuel pump also keep cool in the tank.  When the pump runs dry it can
quickly kill itself.  Use an EFI tank with baffling or an external pump with
fuel reservoir.

PLENUM or upper manifold:
All have cast in Passenger EGRS
Pre 89s have another passage for cold start system--a triangular port
between the 2 throttle openings for the Idle Air Control Circuit.
All Plenums have a port for inlet air temp sensor and a power brake vacuum.
90-92 incorporate vacuum for the map sensor.

SIDE RUNNERS:
The big tubes that connect from Plenum to manifold.
Passenger sides are all the same.
Drivers side varies.  Pre 89 uses the auxiliary injector.
Street and Performance offers a plug kit to mate early runners with later
electronics.
Small tube feeds air to 9th injector--all drivers side units have it.
Smaller runners support higher rpm.

Throttle bodies:
Usually around 48 mm butterflies.
Pre 89 have a small triangular port on bottom which matches to the plenum to
receive air for the IAC.

Distributor:
Ignition systems must be compatible with EFI.
The ECU reads a signal from the distributor to determine injector firing
order.

What do you think?  Does anyone know anymore??  ms


Good judgment comes from experience, and a lotta that comes from bad
judgment.
"Reality will kill you unless you deal with it through myths and metaphors."
Ray Bradbury
Michael Selig, MD, FACC.
www.lifelinecardiology.com