lml@lancaironline.net Mailing List Archive

Gents,

Be careful. Continental injected engines can make use of metered fuel pressure as an indication of fuel flow (consider the pressure regulation returns excess fuel back to the tank from whence it came). See the last chart at

http://www.navion.com/performance/IO550B.pdf

Indeed, my old Skymaster, equipped with Continental engines, used fuel pressure for the fuel flow panel indication.

Generally, Lycoming injected engines generally need some minimally high fuel pressure and the servo controls how much gets sent to the spider. There is no return line in such a set up and the fuel pressure is measured before it is metered. Lyc IO 320 specs call for fuel pressure in the range of 12-46 psi. Generally, you will see many 320/360 maintain a pressure of around 26 psi.

Scott Krueger

IO320

In a message dated 12/6/2011 7:55:27 A.M. Central Standard Time, scottekeighan@sympatico.ca writes:

I routinely see fuel pressures in the 9 to 14 range all the time. I have never had any problems.
This past weekend I was running at 14psi at 6500ft, 2400rpm and 21.5mp, 14.7gph ROP, indicating 190kts with no issues.
It seems the higher I fly the lower the PSI. I believe that it is recommended to run low boost above
10,000ft to help with this issue.

Now, I must admit the first time I saw 9psi it did get my attention.

Scott Keighan
LIV IO-550N

To: lml@lancaironline.net
Date: Mon, 5 Dec 2011 19:24:13 -0500
From: randy@aoaircrafters.com
Subject: [LML] Holy crap

I have been seeing indicated fuel pressures (9 - 13 PSI) on my VM1000 that are too low for the fuel servo (requires around 20 PSI) to operate at - but it continues to operate.

So after checking and modifying the fuel lines (changed from series to parallel for the boost and mechanical pump), removing the mechanical fuel pump and having it checked out at the manufacturer, we decided to just replace the fuel pressure sensor - figuring it would be under $100 to replace.

I called JP Instruments and got a quote of $650. Holy crap.

The technician told me I could field-test the sensor and that it has an output of 1mv per PSI input. ie 5 mv for 5 PSI, 10 mv for 10 PSI, 50 mv for 50 PSI etc..

Does anyone out there want to sell a working-but-not-using VM1000 fuel pressure sensor (the higher pressure one) for fuel injected engines?

Does a guy have any options or FP sensors other than VM1000 brand that put out that kind of output?

Randy Hartman

LNC 2 - N360DE - 450 hours
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