-----Original Message-----
From: owner-dakota-truck@bent.twistedbits.net
[mailto:owner-dakota-truck@bent.twistedbits.net] On Behalf Of
jon@dakota-truck.net
Sent: Saturday, April 28, 2007 5:26 PM
To: dakota-truck-moderator@bent.twistedbits.net
Subject: Re: DML: Can I put an '04 gas tank in a '95 truck?
"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 --'
So if I have a lumpy cam with some overlap (I'd have to look up the exact
specs) which reduced the vacuum at idle, that could cause a rich condition
when idling?
The reason I think it's rich is because it smells rich at idle and 2 new
high flow cats (dual exhaust) got ruined a couple months after the engine
was built (a few years ago now, been running without them).
If this were my case, how could I fix this (besides replacing the cam :)?
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