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Thread: Fluctuating pressure indications

  1. #1

    Fluctuating pressure indications

    I've been flying my 3500 on an RV10 for 1-1/2 years now. Since early on the Manifold pressure indication would occasionally fluctuate (rapidly) to the low side of actual. This trend has increased and also at times showed a stable value far below actual. A few times it displayed zero value. Although I re-did the plumbing to the sensor, I didn't expect this to help since I think a leak would likely show a high value - not low. I changed out the sensor a couple weeks ago.. no fix.

    More recently the oil temp started doing the same thing. Fluctuating from a high number I believe to be accurate to as much as 80 degrees lower. Fluctuations are rapid.

    Just yesterday the fuel pressure started acting similarly. The difference being the low number seems accurate and it will peak to as high as 70 psi. On this one the sensor may be a more likely possibility as it follows a pattern of being high at idle rpm and stable/accurate at anything higher.

    Lastly, on one recent flight (only one) the engine monitor portion of the screen (lower third) would flicker every 10 to 20 seconds. The remainder of the display didn't perform this way.

    These observations don't happen on every flight nor with every pressure indication, however the frequency is increasing. All other engine monitor display items seem to be accurate. Since I ruled out the MP sensor I'm assuming also it's not the other sensors. Am I right to think that this may be related to my AFS 3500 unit? What's the next step?

  2. #2
    Your Oil temp is most likely a loose engine ground strap. Try the Oil temp with all the lights on and then off and see if it changes. Your manifold sensor is most likely the connector crimps or wiring.
    Rob Hickman
    Advanced Flight Systems Inc.

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