[Diy_efi] Donegan ECU

[bearbvd at mindspring.com]

Original Message:
-----------------
From: Bernd Felsche bernie at innovative.iinet.net.au

> When you say 'geared to', do you mean mechanically
> coupled?

Probably not...

> No rules that say the pressure pump can't be close to,

Try the rule of not operating the pump in an environment hotter than
allowed by its specifications. :-)

It is possible to build pumps that'll tolerate under-bonnet
temperatures but off-the-shelf ones, designed for under-tank or
under-body mounting, typically don't.

> or right next to, the fuel rail. In fact, for

Or "in" the fuel rail.

> retrofitting, that can make things easier. That
> eliminates the 'dead end piping' issue.

Diesel engines have worked like that for ages... especially the ones
with unit injector pumps.

Heat is more of a problem with gasoline than diesel; especially
heat-soak. However, the feed pump from the fuel tank can be set up
to flush the high-pressure pump and rail before starting. There are
half a dozen ways that I can immediately think of doing that.

There are a few niggly problems about there being enough of a fluid
pressure damper in the system so that pulsations of fuel pressure
from the pump and the injectors don't wreak havoc with the fuel
pressure control system and to ensure a consistent (intended) fuel
pressure at the injectors. There is sometimes a pressure
accummulator between the high pressure pump and the injectors, and
in some systems a separate damper to handly dynamic fluctuations
(typically when the fuel rail volume isn't "huge" wrt injected
quantity).

The potential problems from fuel piping (and rail) dynamics are HARDLY
'niggling'!!

NOR are the needs to pay attention to keeping vapor OUT of the piping and
rails and for providing adequate NPSH to the high pressure pump under ALL
possible operating conditions.

Those who do not know the words behind the above 'NPSH' acronym, AND
_FULLY_ understand their meaning, but who PLAY with the design of such
systems anyway, quite likely are fully deserving of ALL of the negative
consequences of doing so --after all, there are even reputable vehicle
MANUFACTURERS who reaped serious negative consequences from such ignorance
in the past!!! (Volvo's application of D-jetronic, for instance !!)

Greg

-- 
/"\ Bernd Felsche - Innovative Reckoning, Perth, Western Australia
\ /  ASCII ribbon campaign | "If we let things terrify us,
 X   against HTML mail     |  life will not be worth living."
/ \  and postings          | Lucius Annaeus Seneca, c. 4BC - 65AD.


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