[Vwdiesel] Re: [Audi-VW-Diesels] Vacuum Guage?

[Nate Wall]

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Guess what, diesels don't have manifold vacuum, only gasoline engines
do.  Its because gassers have a throttle plate that is closed to varing
degrees (hense changes in the guage reading according to throttle
position, highest at idle), and the pistons pump against this
restriction.  Its necessary because they must maintain a constant
air/fuel ratio (about 14:1), so less fuel, less air. Diesels, on the
other hand, have no throttle plate on the air intake, so no vacuum.
Engine power is controlled solely by amount of fuel injected, and A/F
ratio varies by great amounts, depending on load.  That's why they got a
vacuum pump to supply the brake booster and climate controls (on various
models), and on gas cars vacuum is obtained for these by simply plumbing
into the intake manifold.

--Nate

jon.sykes at ps.ge.com wrote:

>  I've heard that vacuum guages are a useful indicator of engine wear
> and also
> fuel economy.  I'd like to put one on my diesel Vanagon.  Can anyone
> recommend a particular brand or model - I don't want to spend very
> much.
> Also, where abouts does it hook up to the engine?
>
> Mechanical-ability lacking,
>
> Jon
>
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