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Clearly not crucial ):<), Barry.
Based on my experience with Tracy's Default EC2
settings - it appears that my engine always runs bit rich at idle.
Yes, I can/have adjusted the MAP values to compensate for this but still have a
rather irregular idle at times - acts as if too rich. With the fuel
pressure adjusted to compensate for manifold pressure, then each millisecond of
injector time injectors the same amount of fuel. So I am not certain
as to whether this has any bearing on my idle but when you seem to have
eliminated all else - this remains and makes me wonder.
In my research, I have found this type of description of
what a pressure regulator (manifold referenced) is suppose to do so causes
me to wonder whether I have the correct type. I know I do not have a 0.49
psi drop for each inch Hg drop in manifold pressure. If I have 43 psi at
WOT then according to the description below I should have approx 0.49 * 15 = 7
psi drop in fuel pressure at 15 inch Hg in manifold pressure or - it should drop
from 43 to 35 psi (approx) which it does not.
Ed
To take a fuel pressure reading, you have to remember that during idle, the
vacuum causes the fuel pressure regulator to lower the fuel pressure to maintain
55psi between the fuel pressure and the manifold pressure. For every 1inHg
of vacuum, there is a 0.49psi drop in pressure at the rail. So, 15inHg of
vacuum will make about 47.6psi of fuel pressure on a stock regulator. To
accurately set the fuel pressure, you either have to calculate the proper fuel
pressure by measuring the manifold vacuum, or you need to unplug the vacuum line
from the regulator. This will make the regulator think the manifold is at
0psi of pressure and the fuel pressure will rise to 55psi. Do not leave
the regulator unplugged when you are done! If you drive your car with the
regulator unplugged, the engine will lean-out and severe engine damage could
result! While at idle, the engine will run rich because of the rise in
fuel pressure, so don't do it for too long. With your fuel pressure now at
a constant, atmospheric pressure, you can reliably adjust it. To lower the
fuel pressure, turn the adjusting screw on the adjustable regulator
counter-clockwise. To raise it, turn it clockwise. With the engine
idling, you will see the pressure change on your guage.
----- Original Message -----
Sent: Thursday, September 21, 2006 2:06
PM
Subject: [FlyRotary] Re: Fuel Pressure
Regulator Vacuum or Boost??
Ed,
If stock automotive regulators don't take vacuum
into account (to the best of my knowledge, anyhow), is it
important?
Barry Gardner
Wheaton, IL
----- Original Message -----
Sent: Thursday, September 21, 2006
12:57 PM
Subject: [FlyRotary] Fuel Pressure
Regulator Vacuum or Boost??
For the entire life of my rotary powered RV-6A, I have
flown with a "Boost Referenced" adjustable fuel pressure regulator from
MSD. As you know, it is desirable to keep the pressure differential
between the injector fuel rail pressure and the manifold pressure a constant
for best fuel injection control.
I flew for several years thinking that since my
pressure regulator was manifold reference that it was indeed doing
this. Then the light bulb came on - my fuel pressure holds rock-steady
at 43 PSI - and does not vary between idle and WOT! This certainly
implies that the fuel pressure IS NOT varying as a function of manifold
pressure.
Then doing some recent research on fuel pressure
regulators, I noticed that some say they are "Boost Referenced" and other's
say "Vacuum/Boost Referenced". My conclusion (which may be
incorrect) is that while my pressure regulator is "Boost Referenced"
it is not "Vacuum Referenced". The difference (If I understand it
correctly ) is that my regulator would increase fuel pressure IF it ever
encounter manifold pressure greater than ambient - since I am not used
forced induction that never happens - which in turn appears to be the reason
I never see the fuel pressure changing in response to manifold
"vacuum".
So my question to those who realllllllyyyyyy know -
is it correct that for my NA 13B I need a fuel pressure regulator that
responses to manifold "Vacuum" or is the difference in description between
"vacuum referenced and boost referenced " just semantics in
advertising?
Thanks
Ed
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