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From: rickb@tekig4.UUCP (Rick Bensene)
Newsgroups: net.auto.tech
Subject: Re: Fuel Injection
Message-ID: <459@tekig4.UUCP>
Date: Tue, 14-Jan-86 20:09:31 EST
Article-I.D.: tekig4.459
Posted: Tue Jan 14 20:09:31 1986
Date-Received: Fri, 17-Jan-86 06:47:27 EST
References: <369@cbuxc.UUCP>
Distribution: net
Organization: Tektronix, Beaverton OR
Lines: 49

> Many new cars are advertising different types of fuel injection; multi-port,
> throttle-body, etc.  Would anyone care to give a short tutorial on fuel
> injection in general, and how if any these 'variants' differ from REAL
> fuel injection?  Or are they just names dreamed up by a marketing dept.
> 					Thanks In Advance,
> 						Mike Vehonsky

While I'm certainly not an expert in the field, I think I can shed a little
light on this.

Tuned-Port-Injection: This is used on the Chevy Corvettes and IROC Z/28's
and specially equipped Z/28's.  It involves 8 individual injectors which
inject fuel into the intake manifold runner just before the intake port
of the head.  The 'tuned port' comes from the curved tuned-length intake
tubes which supposedly help increase bottom and mid-range torque.

Throttle-Body Injection.  This uses carburetor-like throttle bodies
which have injectors in them.  They sit on top of an intake manifold
much like a carburetor, but have computer-controlled injector(s) in
them which spray the fuel and mix it with the air.  Used on
early 80's  Corvettes & Z/28 Camaros (with two throttle bodies), and many
newer 4-cylinder applications.

Multi-Point FI:  Much like the Tuned-Port system mentioned above, minus
the 'tuned-port' intake.  Individual injectors feed the intake ports
of the heads.  On some systems, there are more than one cylinder
served by each injector.

All of the above systems are controlled by engine control computer, which
monitors engine RPM, load, throttle position, air/fuel mixture, engine
temperature, mass airflow, and other parameters to determine optimal
fuel mixture.  Most injectors are controlled by a pulse-width modulation
system.  The longer the pulse width applied to the injector, the more
fuel is delivered.  The computer determines the proper pulse widths, and
sends pulses to the injectors to control the mixture.  Some of the
more sophisticated systems control the pulse width to each individual
injector, based on the demands of each cylinder, while others compute
one pulse width, and run the engine through one cycle before updating it,
running all of the injectors with the same pulsewidth.

Hope this is of some help.


Rick Bensene
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