Re: [MV] Authorities

James Shanks (
Thu, 14 Jan 1999 05:32:44 -0500

-----Original Message-----
From: Bob, Jeff and Hoot Gallagher <>
To: mil-veh <>
Date: Thursday, January 14, 1999 1:47 AM
Subject: Re: [MV] Authorities

>>To further
>> enlighten you--a diesel engine does not produce vacuum.
>I admit to not knowing much about diesel engines, is air sucked
>into the combustion chamber without creating a vacuum?

Simply? The same way a gas engine sucks in a mixture of air and fuel, a
piston draws it in as it goes down in the cylinder. A gas engine be it fuel
injected (port injected is one fuel injector per cylinder) or TBI (Throttle
Body Injector is one or two injectors. The number of injectors on a TBI
depends on whether it is a 1 or 2 barrel TBI unit. To a layman it looks like
an old style carburetor). A port injected engine uses a throttle plate which
controls how much air the engine gets. The throttle plate restricts the air
flow to the engine thereby creating the vacuum to run vacuum auxiliaries.
Port and TBI throttle plates all have at the end of the throttle shaft what
is known as a "TPI" (Throttle Position Indicator), this sends a signal to
the computer so it knows (the computer) how far open or closed the throttle
plate is so it can inject the proper amount of fuel to the engine. A Diesel
on the other hand is controlled by controlling fuel injected directly into
the cylinders at high fuel pressure, (there is no throttle plate on a diesel
so they have to use a mechanical device to create vacuum) between depending
on the design 1500 to 2700 PSI (pounds per square inch). Diesels are
mechanically injected where most gas engines still suck the fuel into the
cylinder on the intake stroke (piston going down after the exhaust stroke
sucking in fresh air). Big difference is gas engines use a spark plug to
ignite the fuel/air mix just before the piston hits top dead
center where a Diesel compresses the air thereby raising the temperature to
around 800-900 degrees, the diesel fuel is mechanically injected just before
the piston would be at TDC top dead high as the piston will
rise on it's compression stroke. My apologies at getting long winded here in
my explanation.

James Shanks
(N1VBN is my Ham Radio callsign)

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