"High Pressure SPICA pump"

[JHertzman@domain.elided]

In AD7-524 Jack Hagerty suggests that a reference to "High Pressure SPICA
pump" usually refers to the output of the injector pump, rather than the
supply pump. I believe he is incorrect. In the early days there was much
discussion about the Spica fuel-supply pump. Joe Benson, tech ed of 'Alfa
Owner in he mid and late seventies, wrote (June 1995) "The least reliable part
of the otherwise excellent injection system seems to be the electric Spica
fuelpump. The new Bosch pump is apparently the best cure-"  George Whitcomb,
the prior tech ed, had written (December 1970) of "the noisy, motor-gear type
fuel pump" that "pressure regulation is nowhere near that stated in the f.i.
manual (16-18 psi). Fuel starvation is usually noted below 6 psi". This was
critical because the plungers are both cooled and lubricated by the
recirculating gasoline, and when/if fuel starvation occurs the most wear-
critical parts of the system are going uncooled and unlubricated, which is the
quick route to crankcase dilution and a bill for a new F.I. unit. Several
people tried replacing the Spica pump with other brands of electric pumps,
including some advertised as "high pressure" and ran into problems because
what is considered high pressure for a carburetor system is far lower than
that required for the injection pump.

Also in AD7-524 Eric Hambleton writes "I recall that the Bosch 3-nozzle pump
had to develop the same or higher pressure than the L-Jetronic 2-nozzle pump.
The 3-nozzle variety contained a built-in pressure regulator and provided a
return path via the third tube. Here memory fails me: is there a fuel return
from the Spica injection pump? If so, why?"

There indeed is a fuel return. The FI manual 1502 (4/1969) says "The gasoline
flows from the tank through the tank filter and main filter and feeds the
injection pump. The excess fuel, acting also as a coolant for the injection
pump, before returning to the tank, passes through a calibrated orifice which
regulates the pressure within the injection pump. A pressure relief valve in
the main filter limits the fuel pump outlet pressure bypassing fuel to the
recovery pipe." The original description of the system in Alfa Owner (January
1969) had said "the excess fuel being returned to the tank helps keep the fuel
cool and precludes evaporation of unused surplus fuel- another step toward the
reduction of unburned hydrocarnbons in the air" but this is, of course
incorrect; heating of the fuel through cooling of the pump contributed to
vapor-lock tendencies, particularly on hot days with low tanks.

John H.
Raleigh, N.C.

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