Changing injector pulse rate at idle?

[Michael F. Sargent]

The standard Bosch fuel pressure regulators (and probably everone elses) are
referenced to manifold pressure. That results in a lower fuel pressure at
idle (low manifold pressure), and a higher fuel pressure at WOT (higher
manifold pressure). Typically these regulators produce around 30 PSI fuel
pressure at idle, and go up to about 45 PSI at WOT. Note that as the
intake manifold pressure increased by 15 PSI, so did the fuel pressure.
This results in a consistant pressure across the injector, as well as
providing higher flow as the throttle opens.

There are companies which make "rising rate" fuel pressure regulators.
These regulators increase the fuel pressure at a rate greater than the
increase in manifold pressure. For example, as the manifold pressure
increases from 0 to 15 PSI, the fuel pressure might increase from 30 to
60 PSI, increasing at a 2:1 rate over the manifold pressure.

If you really want to go with computer controlled fuel pressure, I would
suggest measuring the fuel pressure, feeding that into the DIY ECU, and
using a proportional speed controller for DC motors to control the fuel
pump. These controllers are used in radio controlled cars, and produce
full voltage output, but vary the duty cycle. The good controllers use
massive power FETs, and some of the top of the line speed controllers
can handle up to 100 Amps. I don't know the current draw of an EFI fuel
pump, but I suspect that most of the racing speed controllers would work
correctly.

BTW: With this set up, you may be able to get away without a fuel return
line.

Mike
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| Michael F. Sargent   | Net: msargent at gallium.com | Phone: 1(613)721-0902 |
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