"Jamie Calder" <jcalder3@cfl.rr.com> wrote:
> From:jon@dakota-truck.net
> ...thus 1993 was the last year for the return style with a pressure
> regulator in the engine bay. The reason I say that is because you
> can use an inexpensive, "dry" style nitrous system on Dakotas
> through the 1993 model year because they can play with the regulator
> for additional fuel delivery...
> Is it also possible to play with the regulator to decrease the fuel
> delivery? Would you know how?
The fuel pressure regulator uses a diaphragm with a metering
spring and engine vacuum on one side and fuel pressure on the other.
(The fuel pressure is about 10psi higher without vacuum than it is
during a high vacuum situation like idle.) Basically the fuel pressure
generated by the pump is constantly pushing against the spring, and
when it pushes enough to open the spring, the return valve is exposed
and the fuel pressure stabilizes at that point. The vacuum assist
works "with" the fuel pressure in fighting against the spring to open
the return port. (So at idle when vacuum is high, it does not take as
much fuel pressure to push open the spring, hence the fuel pressure at
the injectors is lower, and vice versa, at WOT when there is little
vacuum, the fuel pressure must do all the work and the fuel pressure
will naturally be higher.) (Fuel pressure with this '92-93 regulator
at idle with the vacuum line connected should be about 31psi and about
39psi with the line disconnected.)
Its fairly easy to increase the fuel pressure in a system like
this by basically just blocking off or restricting the return port and
allowing the pressure to build, even after there is enough pressure to
open the spring in the regulator. Decreasing fuel pressure is another
story. I suppose you could increase the vacuum to the pressure
regulator to do this, but that seems overly complex, so the easiest
way to decrease fuel pressure would seem to be decreasing the spring
pressure. (Unfortunately the regulators themselves are non
adjustable.) I have never tried to take one apart, but it may be
possible to dissasemble the regulator and shave down or cut the
spring; this would basically be trial and error. (Dissasemble, shave
the spring a bit, reassemble and test, rinse, repeat.) :-)
You could also install an adjustable, aftermarket fuel pressure
regulator in place of the stock one. You'd probably want to make sure
it uses a vacuum reference though and that the pressure difference
between idle and WOT will be approximately 10psi, as that is what your
computer is expecting. (If it were non-adjustable, it seems like you
would have to set the fuel pressure at about 39psi in order to ensure
adequate fuel at WOT, but this will mean excess pressure at idle
without that vacuum reference. Wether the computer would compensate
by decreasing injector pulse width during high vacuum conditions
without throwing a code I do not know.)
--
-Jon-
.- Jon Steiger -- jon@dakota-truck.net or jon@jonsteiger.com -.
| '96 Kolb Firefly, '96 Suzuki Intruder, Miscellaneous Mopars |
`-------------------------------- http://www.jonsteiger.com --'
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