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Message
Ain't that what they are supposed to do
? Keep it steady as outside pressure diminishes ?
The point is to keep the pressure difference the same
between each end of the injector. Say you have 40 psi of
pressure in your injector fuel rail, and the engine isn't running.
When the injector opens, the fuel rushes from the higher 40 psi end,
to the lower 0 psi end. If you only had 10 psi on your fuel rail, it would
still flow, but not nearly as fast, because there isn't as much pressure
difference. This part is pretty easy to see, but what people forget about
is that the pressure on the intake side of the injector matters too.
Say you have your same 40 psi on the fuel rail, but now the
engine is running at idle, with 20 inches of vacuum (-10 psi
roughly). Now, there's a 50 psi difference from one end to the
other. Say you run the engine with a turbo set to 10 psi of
boost. Now there's only 30 psi of difference in pressure. This
relationship is exactly opposite of what we want, because we want more fuel at
high power, and less at low
power. The
computer can compensate for this to some extent, but at some point, there are
limits to what you can do with injector
timing.
The best way to handle this is to use the intake
pressure as a reference, to vary the fuel rail pressure. Now, if the
intake pressure rises, or falls, the fuel rail pressure follows it, so the
pressure difference on each end of the injector stays the same, and fuel sprays
the same when you open the injector. Make
sense?
Cheers,
Rusty (stop me before I buy another
project)
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