Finn,

Rather than coming up with a way to electronically reduce or eliminate the pressure pulse measurements, you might consider reducing or eliminating the pressure pulses in the first place.  It is my understanding that the (leak prone) stock pulsation damper results in quieter injector operation.  This makes sense if the injector, when it starts to close, is being slammed shut with pressure pulse of at least 25 psi over the normal fuel rail pressure when the damper isn’t present. It’s hard to imagine this as a good thing, but maybe that’s just me.  Similar pulses may be occurring at the dead ended primary injectors but you aren’t set up to see them.

I chose to plumb the primary and secondary fuel rails in series and installed about 2 ft of fire-sleeved hp rubber fuel injection line at the end of the series.  The hope was that this rubber line would act as a more reliable pulsation damper than the stock unit.  I say “hope” because my fuel pressure regulator, pressure sensor, fuel pumps, filters, and selector valve are all located in a module in the cockpit and vented to outside of the fuselage.  As a result, I have not tried to measure the pulse amplitude at the end of a rigid fuel rail and don’t really know how effective my setup is.  I do know it has been reliable so far (over 700 hr) and that I got steady fuel pressure readings initially with a homemade logger and later with a Dynon EMS D10.

I also provided a MAP reference to the fuel pressure sensor so the fuel pressure reading shows the pressure across only the injector and does not reflect changes in MAP or altitude.

FWIW

Steve Boese


> On May 6, 2021, at 5:47 PM, Finn Lassen finn.lassen@verizon.net <flyrotary@lancaironline.net> wrote:
>
> OK, so I hooked up a scope to the fuel pressure sensor.
> Sensor has 50mV/psi sensitivity.
> Below 20"Hg (secondaries not opening) just very slight pulses.
> But above 20"Hg -- about 4100 RPM -- I see 1.24V or 25psi peak-peak  pulses.
> So that explains the wildly fluctuating fuel pressure readings. Depending on when the pressure sensor voltage is sampled by the engine monitor there can be 25 psi or more difference in engine monitor readings and data logging.
>
> If you look at the picture I attached on May 4th, you'll see the pressure sensor is located at the end of the secondary fuel rail (solid tube) . Apparently the rubber lines from the T-fitting to primary and secondary rails are enough to somewhat dampen the primary injector fuel pressure pulses. I probably should add an R-C filter between sensor and monitor to get more reliable fuel pressure readings.
>
> With today's 15 deg F lower OAT the engine transitions smoothly at the staging point. I'm again seeing cracks in the JB-weld around primary runners, so possible that they may be collapsing somewhat under high ambient temps -- maybe not. Remember I'm using the stock exhaust manifold. Even with the stock heat shield and an additional 0.016 alum shield, the heat from the exhaust manifold is intense. That is a huge chunk of metal that'll radiate heat with low or no airflow over it after shutdown. A definite drawback from using the stock exhaust manifold. Maybe I don't have a leak in my welds on the exhaust manifold and it was just higher OATs?
>
> Another suspect for odd behavior is the engine controller's temperature sensor. I located it in the left radiator air scoop. Probably a bad idea when running on the ground.
>
> Finn