I've never heard of it happening on a setup with an in-tank fuel pump,
carburetor or FI. Because the fuel is constantly circulating, it never gets
that hot, and the high pressure in the system (esp. with multi-port FI)
keeps the fuel from boiling.
Robert Hancock Saskatoon, SK, Canada
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It is a laws of physics at work, gasses compress. and liquids do
not. If one were to try pulling against atmosphere one can only
draw a vacuum of 30 inches of mercury ASL, no mater how big the
pump. When the pump is above the liquid, as in older cars trying
to 'pull' gasoline to the pump, and there is vapor present in the
line, it is not possible to extract the fluid. In the case of the
pump being below the liquid, as are today's pumps there in no
'lift' on the intake side at all. The discharge side of the pump
will push liquid up to the 'head' pressure of the pump. In other
words, vapors are pushed on the discharge side of the pump, but
can stop it from pumping on the intake side of the pump.
Robert Hancock wrote:
I don't know if it was vapor lock, but some cars made in the 1970s
with Bosch CIS fuel injection (continuous, mechanical, about 70 PSI)
had hot start problems that were solved with a larger fuel
accumulator. This accumulator was a bladder that kept the fuel system
pressurized even when the engine wasn't running.
One thing some of the other posters haven't recognized is that with any type of
fuel pump that is mounted outside the fuel tank, there is a suction line.
Inside any suction line, pressure is lower than atmospheric (that's how the fuel
moves--atmospheric pressure pushes it toward the point of lower pressure). Any
time a liquid's pressure is reduced, so is the temperature at which it boils.
(Ever boiled water at high elevations and noticed it wasn't very hot?)
Anyhow, with any fuel pump mounted near the engine, the fuel line from the tank
to the pump is at a low pressure, and can be subject to heat from the
environment, or from exhaust components. This is where vapor lock problems
occur. Do away with any suction lines, and the vapor lock problem goes away
Gerard's Automobile Book, Video, and DVD Store
On Sat, 26 Jul 2003 02:01:49 GMT, firstname.lastname@example.org wrote:
Very few vehicles built in the past 15 years or so only use a single
external fuel pump. Of those that do, the 'suction' line is
intentionally as short a possible. I don't know of any that have the
fuel pump any where near the engine.
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