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Thread: Fuel Pressure Sender - Failure Mode?

  1. #1

    Fuel Pressure Sender - Failure Mode?

    Every once in a while I get a high fuel pressure indication and warning in cruise flight, where pressure spikes up to 50ish psi for a few seconds (fuel injected engine, Bendix RSA-5 servo). Research tells me that the engine mounted mechanical fuel pump is not capable of making this pressure (electric fuel pump is off).

    Could this be an intermittent fuel pressure sensor electrical connection? Any idea what the fuel pressure displays when the sensor is disconnected? Do any known failure modes explain this behavior?

    Thanks,
    Highest Regards,

    Noah F
    RV-7A
    Rhode Island

  2. #2
    Quote Originally Posted by NoahF View Post
    Every once in a while I get a high fuel pressure indication and warning in cruise flight, where pressure spikes up to 50ish psi for a few seconds (fuel injected engine, Bendix RSA-5 servo). Research tells me that the engine mounted mechanical fuel pump is not capable of making this pressure (electric fuel pump is off).

    Could this be an intermittent fuel pressure sensor electrical connection? Any idea what the fuel pressure displays when the sensor is disconnected? Do any known failure modes explain this behavior?

    Thanks,
    Could be a loose wire or sensor going bad.
    Rob Hickman
    Advanced Flight Systems Inc.

  3. #3
    Quote Originally Posted by Rob Hickman View Post
    Could be a loose wire or sensor going bad.
    Right, but does the sensor indicate 50+ psi when the wire is disconnected? Mine is hardwired so there is no easy way to disconnect it.
    Highest Regards,

    Noah F
    RV-7A
    Rhode Island

  4. #4
    Similar issue with mine recently - had the cowl open so I released the pressure (if any) by disconnecting the sense fuel line from the mechanical pump to the sensor...then I gently tapped on the sensor. Similar issue with mine recently - had the cowl open so I released the pressure (if any) by disconnecting the sense fuel line from the mechanical pump to the sensor...then I gently tapped on the sensor. Things returned to normal. Next flight was fine...next one had the PSI elevated until after warm-up and take-off.

    I have also recently had an issue with the AN-6 sized fuel inlet finger strainer (50 micron - I think) being clogged with a fine black substance. It is after the outlet from the mechanical pump - if some of that has migrated up to the fuel pressure sensor, it could be causing this type of failure mode. I'm adding another more easily serviceable filter in front of that which will be part of the annual inspection sequence

    I'll be taking mine off this weekend as part of an oil change cycle - I'll try to clean it. I think the best I'll be able to do though is rinse it out as the sensor intake hole is small. Probably going to order a spare sensor - just in case....remembering there are at least two types of high pressure FI applicable sensors - I have the newer VDO/silver/80PSI...replacing the earlier SW/gold/60PSI unit a couple of years ago.

    I'll post cleaning and post-cleaning flight results here as it might be pertinent.

    Hope this helps,
    Ralph

  5. #5
    Thanks for the info Ralph.

    Quote Originally Posted by recapen View Post
    there are at least two types of high pressure FI applicable sensors - I have the newer VDO/silver/80PSI...replacing the earlier SW/gold/60PSI unit a couple of years ago.
    Any idea why the pressure sensor changed from a 0-60 to a 0-80 psi model? Any changes required in the EFIS for the new sensor? I think I'll need to pick up a new sensor as well.

    If you're talking about the strainer at the fuel injector servo inlet, I have taken mine off at every annual and never seen anything in it.
    Highest Regards,

    Noah F
    RV-7A
    Rhode Island

  6. #6
    In my case, the sensor failed internally - vibration took out the internal ground - right after take-off. Other indications were normal but I circled back around to an uneventful landing.
    If I recall correctly, the follow-on conversation centered around the SW being less tolerant of the vibration that aircraft are subjected to during landings - but both are still available. I used VDO stuff in my old air-cooled VW's years ago. You do need to change settings in the Engine Monitor to accommodate the different device type.

    By now, I think I have had the new one installed longer than the original lasted so I am inclined to stick with the later version.

    Yes, same strainer - mine was able to actually hold fuel instead of filtering it when I removed it for cleaning. I have an AirFlowPerformance system - Don and his crew have been very good support-wise!

  7. #7
    I was able to get mine removed this weekend as part of a scheduled oil change.
    I shook out the original fuel that was in it - the hole was small so I am not sure how much I was able to get back in there to rinse out with.
    Dried it off, fresh fuel-lube on the threads, back in it went - wired it up and couldn't fly cuz of the weather....

    I'll be ordering the spare sender regardless....

    Let you know the results of the flight - after it happens!

  8. #8
    Flight results were good - sender acted like it was a brand new one.
    Don't know whether I was able to actually clean it or simply shaking the old fuel out was sufficient.

    New sender to be ordered shortly as a spare....

    Ralph

  9. #9
    Are any calibration changes required if going from the old silver VDO to the new gold Stewart Warner fuel pressure sensors?
    Last edited by NoahF; 08-04-2014 at 01:10 PM.
    Highest Regards,

    Noah F
    RV-7A
    Rhode Island

  10. #10
    Advanced Flight Systems Shawn McGinnis's Avatar
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    You should be able to select the part number from the fuel pressure calibration page.
    Shawn McGinnis

    Advanced Flight Systems
    support@advanced-flight-systems.com

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