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Theschultzfamily(at)comca
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 Posted: Tue Jun 30, 2009 7:03 pm Post subject: Fuel system - More Questions! |
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Fuel problems are just what I am currently looking at as the possible cause of my intermittent rough running engine. Has anyone taken the time to check the calibration of there sender unit to see how accurate it is? And if so what fuel pressure you are seeing at different manifold pressures?
I don’t trust the accuracy of my gauge and am I the process of running a calibration table to see how it responds over the range of 3 – 15 psi. I hooked up an analog pressure gauge I picked up from AutoZone over the weekend and it gave me a moment of pause. The base reading at idle was about 4.2PSI as I went up to about 31 inches the gauge was seen to slowly climb to about 6 and then was jumping rapidly between 6 and about 10psi. Not sure what if anything the gauge has for damping but it did not look like any. My UMA gauge never shows a pressure fluctuation of more then maybe .1.
I am taking a small air regulator and making a calibration stand to check the analog gauge against the sender unit and a calibrated pressure gauge I have. This should allow me to know voltages and pressure readings and set up the EIS to read correctly over our pressure range.
I want to know what people see from the 914 at say 15, 20. 25, 30 MP. Not differential but actual pressure.
Problem remains intermittent rough running engine starting about 25MP. When is runs rough both carb vacuum readings are in sync, Changing left or right mags has no effect, Left or right tank has no effect, One, both or other fuel pump has no effect. Going to manual on the prop has no effect as does switching the disable on the TCU. Start and re try and still runs rough. Put the plane away and come back two days latter and it works great. Let it sit a day and it might work or it might not….. Oshkosh is calling and I am afraid I’ll be hanging out in my hanger at this rate L
Rich Schultz
N262AE
180 Hours
[quote][b]
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rparigor(at)suffolk.lib.n
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| Posted: Tue Jun 30, 2009 11:35 pm Post subject: Fuel system - More Questions! |
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Hi RichAs far as your intermittent rough running, a few ideas:When motor begins to run rough, what happens if you turn off both pumps? Does that help? If so you may be above 5 lbs differential or your needle valve and seat may be leaking.Is rubber holding your carbs the Kevlar reinforced and no cracks or leaks?Are you absoluetly certain that you are getting butterflys opening the same? Intermittent throttle cable kinking?Are both your choke cables allowing full closure?Did you check if carb diaphragms have hole or rip and that slides are free to move up and down?Is your fuel tank vent clear?Are you certain plumbing that allows airbox pressure to pressurize carb float bowls are in order?Ron Parigoris [quote][b]
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Theschultzfamily(at)comca
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| Posted: Thu Jul 02, 2009 5:12 pm Post subject: Fuel system - More Questions! |
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Can anyone verify these “non” differential fuel pressure readings?
MP = 14.3 Fuel = 4.6
MP – 14 Fuel = 4.9
MP = 20 Fuel = 4.9
MP = 25 Fuel = 6.4
MP = 30 Fuel = 9.1
MP = 39.5 Fuel = 11.6
Engine seems to be running fine with these but earlier in the process the engine was once again surging. Everyone that hears the surging thinks I have a fuel problem????
Monitoring and testing continues…..
Rich Schultz
N262AE
[quote][b]
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rparigor(at)suffolk.lib.n
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| Posted: Thu Jul 02, 2009 6:48 pm Post subject: Fuel system - More Questions! |
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Hi Rich"Can anyone verify these "non" differential fuel pressure readings?""Non" differential numbers are useless unless you know a lot more information.You need to know differential pressure going to the carb float bowls over airbox pressure to help you figure if you have a problem >>>>>>>>>>> period.Measure airbox pressure in absolute terms and fuel pressure in absolute terms and make sure fuel pressure is between 2 and 5 PSI over airbox pressure. Now when you start increasing MP tell us if it ever falls below 2 PSI. I guess if you really wanted to, if you think your fuel pressure gauge is accurate, add to it the weight of the air that is above you, then add an inch to MP pressure, now subtract what your fuel pressure gauge is reading plus the air above you, from the MP plus one inch. If you are between 2 and 5 PSI above with fuel pressure you are OK. That is the verification you can do yourself.Why don't you just buy a differential transducer from UMA and either one of their gauges or run one of yours from it? This way you can see if you have a problem "RIGHT AWAY" when something is going on.If you take off and either overboost or something else has a problem, instead of waiting for your motor to play silent night or slump, you can reduce MP till you get at least 2 PSI and can be fairly sure you can maintain that power setting.If you fly a 914 IMHO you want differential pressure information.Ron Parigoris [quote][b]
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budyerly(at)msn.com
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| Posted: Thu Jul 02, 2009 8:12 pm Post subject: Fuel system - More Questions! |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Rich,
I'll run mine or Bakers tomorrow, weather permitting, and see what my fuel pressure does. If memory serves, I start at 4 psi at idle and at full throttle still see about 4 in line, and about 10.0 off the regulator (my sender reads a little low). My gut feel is that regulated fuel pressure is going up with manifold pressure as it should, but if line pressure is going up to the regulator, that does not pass the common sense test. On ground tests, the fuel pressure goes up as the resistance goes up.
Example:
When I set up a fuel system, I disconnect the feed and pressure gauge from the engine fuel regulator and pump fuel through the lines past a direct reading pressure gauge (Tee'd to the aircrafts sender) and through a valve to a gas can. This allows me to filter the system, verify flow rates (by timing) and by closing off the valve, I can verify the fuel pressure, the fuel flow decreases and the pressure goes up well above 7 psi as I check flows and verify pressure readings. Note: These readings are done before the regulator.
11.6 psi indicates a strong reduction in flow if reading prior to the regulator, however if you are reading from the regulator, the regulated pressure at full power 39.5 MP is about 5 psi boost, and 11.6 psi fuel pressure is a tad high.
From Page 9.2.3 of the Rotax maintenance manual, Fuel pressure =Airbox pressure + 250hPa At takeoff performance the fuel pressure is going to be about 700hPa or around . 7bar or about 10.15 psi
I'll talk to you after testing.
The shop took a lightning strike and power surge, so I have only one shop phone left and it blew my shop computer, even with the surge protectors. Pretty spectacular really. Snap crackle pop all in one. I will be slow at answering emails for a few more days.
Bud
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Theschultzfamily(at)comca
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| Posted: Fri Jul 03, 2009 5:53 am Post subject: Fuel system - More Questions! |
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Bud,
The reading was taken off the double banjo that feeds the passenger side carb. This as done when the engine seemed to be running correctly.
Being at sea level and with about a 29.8pressure day I figured these did not sound too bad. I do have the original differential pressure sender. I will fire it up at work on Monday and see if it is reading correctly before installing it or ordering a new one. Aircraft spruce is very proud of that little sender now days.
From: owner-europa-list-server(at)matronics.com [mailto:owner-europa-list-server(at)matronics.com] On Behalf Of ofamerica.com YERLY
Sent: Thursday, July 02, 2009 11:11 PM
To: europa-list(at)matronics.com
Subject: Re: Fuel system - More Questions!
Rich,
I'll run mine or Bakers tomorrow, weather permitting, and see what my fuel pressure does. If memory serves, I start at 4 psi at idle and at full throttle still see about 4 in line, and about 10.0 off the regulator (my sender reads a little low). My gut feel is that regulated fuel pressure is going up with manifold pressure as it should, but if line pressure is going up to the regulator, that does not pass the common sense test. On ground tests, the fuel pressure goes up as the resistance goes up.
Example:
When I set up a fuel system, I disconnect the feed and pressure gauge from the engine fuel regulator and pump fuel through the lines past a direct reading pressure gauge (Tee'd to the aircrafts sender) and through a valve to a gas can. This allows me to filter the system, verify flow rates (by timing) and by closing off the valve, I can verify the fuel pressure, the fuel flow decreases and the pressure goes up well above 7 psi as I check flows and verify pressure readings. Note: These readings are done before the regulator.
11.6 psi indicates a strong reduction in flow if reading prior to the regulator, however if you are reading from the regulator, the regulated pressure at full power 39.5 MP is about 5 psi boost, and 11.6 psi fuel pressure is a tad high.
From Page 9.2.3 of the Rotax maintenance manual, Fuel pressure =Airbox pressure + 250hPa At takeoff performance the fuel pressure is going to be about 700hPa or around . 7bar or about 10.15 psi
I'll talk to you after testing.
The shop took a lightning strike and power surge, so I have only one shop phone left and it blew my shop computer, even with the surge protectors. Pretty spectacular really. Snap crackle pop all in one. I will be slow at answering emails for a few more days.
Bud
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budyerly(at)msn.com
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| Posted: Fri Jul 03, 2009 3:51 pm Post subject: Fuel system - More Questions! |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Rich,
Like I said, just a tad high. I'm going to the airport tomorrow again. Rained out today and had to clean up the shop for the UCF senior design team coming in and pushing to get another plane finished up. The boys seem to be going two steps forward and one back on projects, and we're running a bit behind....
Hope the sender works OK. That in conjunction with the data download from the computer and other readings of pressure etc. will tell the story.
Bud
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budyerly(at)msn.com
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| Posted: Sun Jul 05, 2009 5:45 am Post subject: Fuel system - More Questions! |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Rich,
Call on the cell as I'm all over the place this week.
My runup on Saturday was on Baker's 914
The FP was 4 psi solid until boost started to kick in.
4 PSI until passing 30 inches.
Max continuous 100% throttle at 35 inches mp, airbox at about 2.5 psi boost fuel pressure 5.9 to 6.2
Full 115% throttle at 40 inched mp, airbox at about 4.8 psi boost, fuel pressure 9.8-10.
At full it should have only gone to about 9 for the atmospheric pressure, but I read 10, and that's in limits.
Setup was a boost gauge on the airbox, direct reading gauge on the fuel pressure nipple with the restrictor pressed into the end of the brass banjo. Sure wish I had it mounted better, what a vibrating nightmare until I wire tied the mess together.
Look at the maintenance manual and you can see by all accounts you are reading just a little high.
Pay attention to the chart on page 9.5.2 of the maintenance manual, and do the conversions for the airbox pressure, and fuel pressure.
I'll be on the cell as I have UCF students doing their project and test flying this evening weather permitting.
Bud
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