Re: [MV] Diesels Suck

Richard Notton (
Fri, 15 Jan 1999 08:32:13 -0000

-----Original Message-----
From: jonathon <>
To: <>
Date: 15 January 1999 04:36
Subject: Re: [MV] Diesels Suck

>>Diesels do have suction(vacum)
>>Land Rover has a vacum control unit that fits on the intake manifold
>>uses a butterfly to control.This is for the power brake units to
>That's a strange one. With my Diesels, even a dirty air filter causes
>to start blowing black smoke, this kind of thing would do wonders on my
>engines, not to mention my niehbors.
>Life IS stranger that fiction.

Not really.

Your choked air filter produces the same restriction over the whole
engine rev range whereas the manifold butterfly is operated by the
accelerator pedal and admits air proportionally to demand.

Its an old fashioned technique but many diesels here had a vacuum
controlled injection pump. This used a regular accelerator pedal
operated manifold butterfly to produce a vacuum signal that operates a
diaphragm in the injection pump connected to the injection piston
control rack.

A relatively small depression is caused by the butterfly valve as it
would be set at something like 1/4 open to obtain idle revs and not
quite full open for maximum revs, at both limiting conditions adequate
air is passed for complete combustion.

The system can be found on several W.W.II era diesels but it was dropped
later in favour of the more accurate and reliable integral centrifugal
or oil governing system contained in the pump itself.

The vacuum system of governing can fail in a disastrous manner if the
interconnecting pipe leaks causing over revving or complete engine
run-away and is open to "unauthorised" tampering of the butterfly stop
settings. It is also common for the engine to "hunt" badly at idle
owing to insufficient control loop damping at the low end of the rev

(Southampton UK)

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