Re: Fuel Pump - Vapor Lock Woes

["Jay Mackro" <jmackro@domain.elided>]

ARV28@domain.elided  had written:

>Subject: 76 fuel pump hick-ups
>
>Scenario: Fuel pump runs well for a while (1 hr driving or so), then low
>pressure light goes onLet it sit for 1 hr, did not try to start it until it
>built enough pressure and light went out
>During acceleration, light comes on sporadically, changed the  main fuel
>filter in the engine compartment,
>There is the famous 1/2" in/out inline filter still to replace. Does
anyboody
>carry these? IAP states no longer made....

I too own a '76 spider, and I could write a book about this problem.
It's vapor lock - it is aggreviated by several factors:

- - Rear fuel filter (yea, that one you haven't yet replaced) creating
a restriction which the fuel pump must pull against

- - Fuel in tank getting warmed by exhaust, ambient air, and fuel
returned from FI pump

- - Low level of gas in tank, which both decreases mass of fuel which
is warmed by factor #2, as well as increases the height that the fuel
pump must draw the gas up.

So, the quickie fix is simply to top off your tank, and keep it above
half full.  The medium term fix is to replace that rear fuel filter - any
aftermarket, metal filter with the appropriate sized inlet/outlets
will work (yea, I know - someone is going to challenge this - well,
I still say that a new aftermarket filter is better than an OE filter
of unknown condition).

You might also check the fuel evaporation emission control
system.  There is a vacuum line from the engine back to a
charcoal canister in the trunk.  I don't fully understand this
system, but supposedly if a valve sticks shut, it will subject
the fuel tank to a vacuum that makes it harder for the fuel
pump to draw out the gasoline.

There is probably nothing wrong with your fuel pump, and there
may not even be anything wrong with that rear fuel filter (though
I would change it if it hasn't been done in awhile).  This is just
a weakness on the mid '70's spiders.  In later years, Alfa
added a second fuel pump in the tank, so that the line between
the tank and pump wasn't under vacuum.

Jay Mackro

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