Re: SPICA injection and wear

[James Montebello <jamesm@domain.elided>]

On Sun, 24 Nov 2002, C M Smith wrote:
> Of course the main problem with adapting a diesel injection system to
> gasoline use is diesel fuel is a lubricant and gasoline is a solvent. That
> is why the SPICA distributor (some refer to it as a pump as it seems to
> fill that function, but in truth the "pump" portion is merely a distributor
> or metering device) requires an oil supply and why most problems

No. The pump is, in fact, a pump.  More accurately, it's four small
piston pumps (eight for a Montreal).  The diesel pump the SPICA is
derived from has to inject either directly into the cylinder or into a
pre-chamber very late in the compression process, so it has to be under
very high pressure to overcome the pressure in the combustion chamber.
Each little piston pump delivers the fuel in the gasoline version at
something near 100psi, which is why there are hard lines from the pump
to the injectors (which are, in fact, just spring-loaded valves, set to
only open above something like 70psi).  The fuel pressure supplied to
the injection pump is only 7-9psi.  In this, it is very similar to the
Bosch MFI, Kugelfischer, and Lucas mechanical injection systems.

The Bosch K-Jetronic system has an actual fuel distributor/metering
device.  In this system, the 100psi fuel pressure is supplied by a
separate electric pump and a fixed mechanical regulator.  The distributor
only regulates the amount of fuel based on the airflow demand of the
engine, and all of the cylinders receive the same amount of fuel, which
is constantly flowing to all of the cylinders (the K stands for the
German word for constant) the entire time the engine is running, only
the volume of the flow changes with demand.

In the pump-type mechanical systems like SPICA, the fuel only flows some
of the cylinders at any given time.  In the four-cylinder SPICA pump,
only one cylinder is fed at any given time, timed to coincide with a valve
event on that cylinder.  Such systems are referred to as sequential, and
the EFI systems fitted on most cars today are sequential over at least
part of the engine speed range, which improves emissions and economy.

james montebello
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