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Thread: Fuel Flow Indication Abnormality

  1. #1
    Steve Pierce's Avatar
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    Fuel Flow Indication Abnormality

    Cathy and I flew my Super Cub up to Kirby's fly-in east of Tulsa lat weekend. Had a great time playing on the sand bars on the river with the guys and at Sand Springs for a pumpkin drop and lunch. My Super Cub has an Electronics International FP5L fuel flow gauge which I really like in my Super Cub because I rarely fill the tanks up and 90 percent of my flying is local with 6-12 gallons of gas banging around on local gravel bars. The FP5L makes it easy to know how much fuel I have when the site gauges don't show anything in the 3 point attitude. It was 28 degrees the morning we left so I drug the airplane up to the fuel pumps with my small tilting trailer instead of starting it up in the cold. Our planned departure was several hours later. I topped off the tanks and took the airplane down to my main work hanger. Cathy flew the 2.5 hours up to the fly-in and informed me I had not programmed the fuel I had put on. I added some fuel at Sand Springs and guessed at what I had onboard, I didn't want to top off because we intended to do some more playing on the river and a full fuel load makes for poor performance and with the guys I was flying with I needed everything to my advantage because we tend to push the envelope a bit. The next morning we departed our friends strip and flew over to Okmulgee where I topped off and entered my fuel load. On the return trip we were paying for our 110 mph ground speed up seeing 55-75 mph ground speeds averaging 65-68 staying just above the tree tops most of the way so the ground speeds weren't even worse. I usually cruise at 2500 rpm and 7 GPH with the 8241 Borer prop, fuel flow goes up a gallon plus with a Sensenich 7258. I noticed the FP5L wa showng about 12 plus gallons an hour which got my attention. Monitoring the fuel gaug I could tell we were not burning that much fuel and could make the 3.5 hr trip home with one pit stop to pee.

    I had to call Electronics International on another matter so I asked them what they thought of my abnormal fuel flow reading. the tech guy I spoke with thought I had inadvertantly hit a button wrong and changed the K factor on the fuel flow transducer when I entered the fuel on board. Yesterday after work I went out and checked the K factor and it seemed to be in line with the factory K factor, not almost double what it would be to show the fuel flows I was seeing. I called EI back and got a different tech guy and explained to him what was going on and he thought I might have some air bubbles trapped at the transducer. I kind of doubted this since it has worked flawlessly for many years. I hit the quick drain on the gascolator and say a lot of red liquid come out. Ah oh, I know what that looks like. I went and got my sump jar and sure enough I had some rusty water. Sumped both tanks and got a little more but most was in the gascolator. Let it sit a bit several more times until I got nothing. I took it up and stayed in the pattern and noticed my fule flow indications were back to normal. Called EI back and told them what I had found for future reference. I will for sure store it away for mine. Not sure where the water came from but have a sneaking suspicion it was last week when I pulled up to the gas pump and the airport manager said there was an issue with the pump on their fuel tank. He filled a couple of 5 gallon cans from the tank bottom and I checked it for water but found none but was prudent in sumping my tanks later. Lesson learned. Thought others might find this interesting and might helps someone else down the road sometime.
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    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
    Thanks CharlieN, Sam D, KevinJ, CamTom12, 8GCBC and 2 others thanked for this post

  2. #2

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    You set K factor with EI instruments? I had to do the K factor procedure with my JPI but with the Garmin they say the EI red cube is dead-on so there’s no K factor adjustment.

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    Steve Pierce's Avatar
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    It comes preset and is pretty dang close. It depends on how you fly, lots of short hops with many landings or long cross countries but still within 1/2 gallon.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

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    A good reminder to sump your tanks. I admit to not doing it near enough.

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    Water makes your indication go up? Odd. It makes mine with the JPI go down.

    Run some isopropyl through the tanks. There’s probably some water left in the carb. Ever use MMO in fuel? The red dye sticks to water. It’ll teach you a lot about condensation, and your TX temp swings could lead to some of that.

    So you guys don’t sump before the first flight of the day? I can’t imagine not doing it. That and checking oil.
    Last edited by stewartb; 11-09-2019 at 10:08 AM.

  6. #6
    wireweinie's Avatar
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    Water has a different density than gas (gallon of water weighs more than gallon of av gas). Weirds out the transducer, which results in incorrect reading.

    Web
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    Steve, is your transducer upstream of your strainer?

  8. #8
    TurboBeaver's Avatar
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    Steve,
    I have same set up you do. This system is down again for the fifth
    transducer........... Have no idea why last one went on in August lasted only,
    7 hrs. Shut plane down working perfectly, however next morning , it was dead again . Tech called and told me how to troubleshoot the system. I did and it confirmed the transducer has failed again.........others get years out of a transducer , but this one has a horrible history of loosing transducers. Wonderfull instrument to have with " waterlogged" corks in original 12 site guages that indicate empty when there is over 2 hrs fuel onboard!

    Sent from my LM-X210 using SuperCub.Org mobile app

  9. #9
    Steve Pierce's Avatar
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    I didn't sump this past weekend, lesson learned for sure. I just drained both tanks, pulled the gascolator bowl and drained the carburetor. About to pull the gascolator screen and carb inlet screen. Bottom of gascolator is pretty nasty. Since I am certified I installed the transducer per EI's instructions, short flex line off the gascolator to the transducer and another short flex line to the carb. Slight uphill cant to the transducer on the way to the carb which EI told me will keep from trapping air bubbles. I got complacent and it took a good slap of reality but lesson learned.
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    Steve Pierce

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  10. #10
    jrussl's Avatar
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    Quote Originally Posted by Steve Pierce View Post
    It depends on how you fly, lots of short hops with many landings or long cross countries but still within 1/2 gallon.
    Somewhat off topic.........I have noticed the above too with my EI CGR-30. The fuel flow is dead on with long legs but it over estimates the flow when doing local flying with lots of landings.

    Have you ever discussed this issue with EI? Curious as to what is going on. I wish mine was correct all the time.

    Thanks

    Jeff

  11. #11
    Steve Pierce's Avatar
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    I did, I tweaked my K factor a long trip to Idaho and EI told me it would be different than if I tweaked with short flights. Mine is still pretty close most of the time but when I was adding out of 5 gallon cans I would get off a bit. Since I very rarely fill up because I don't usually go far I drain the system from time to time and adjust the amount I have onboard in the monitor.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
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