rotorman Posted July 31, 2022 Report Posted July 31, 2022 To start with, there was a discussion on this topic a while back but the issue went unresolved. In my case my fuel pressure had been normal in my 100 hr IO360 A3B6. Normal to me is somewhere close to the middle between 15 and 30, boost off. I can't say exactly because it wasn't memorable. But it has become memorable during the last couple of flights since it is sitting at the max limit of 30. Powering back to 2500 rpm brings it back about 1 psi so it does stay in limits. The concern is the change. What could be the cause of a sudden noticeable increase? Quote
PT20J Posted July 31, 2022 Report Posted July 31, 2022 First thing I would do is verify that it's not an instrumentation issue by plumbing in an analog gauge and comparing it to the installed gauge during a ground run. 1 Quote
rotorman Posted July 31, 2022 Author Report Posted July 31, 2022 I agree. That would be the first and easiest step. It would put to bed any question of the gauge or the transducer. But assuming that works out OK what could cause OP to run high? Is the pump adjustable? Is there anything else in the oil system that could cause high pressure? As a quick check without putting a gauge on it, how much pressure does the electric pump put out? Mine shows about 20 psi. which has remained constant as opposed to the sudden rise of the engine driven pump. Quote
PT20J Posted July 31, 2022 Report Posted July 31, 2022 The the pump pressure is not adjustable. The fuel pressure should vary inversely to the flow. The highest pressure should be at idle and the lowest pressure should be at rated power. You mentioned that you a 100 hr IO-360-A3B6. If it came from Lycoming, I know that Lycoming switched fuel injection vendors a while back from Precision Airmotive to AvStar. The AvStar seems to have much tighter idle cutoff valve than the Precision units. The original RSA design is supposed to have a small amount of leakage at idle cutoff to provide an air bleed for any gas bubbles that form in the fuel lines in the hot engine compartment after shutdown. I have an AvStar and note that the pressure quickly climbs off scale after shutdown. It hasn't seemed to harm the transducer for my G3X, but I did have the original Kulite fuel pressure transducer fail (it read 0). I don't know if that was caused by this overpressure or not. Skip 1 Quote
cnoe Posted July 31, 2022 Report Posted July 31, 2022 I had the (electric) fuel pump from my J (IO360-A3B6D) overhauled recently and the spec'd fuel pressure for the Dukes 1499-00-19 (14V) is: 35 GPH @ 21 PSI and 25 PSI Max. As Skip mentioned, the mechanical pump isn't field-adjustable. First thing I'd do is make sure that the hose to your transducer isn't full of liquid fuel. Also the tiny orifice into the transducer may be gunked up causing inaccuracy. Then tee'ing into the line at the transducer will tell you if it's an indication error. CNoe Quote
Fly Boomer Posted July 31, 2022 Report Posted July 31, 2022 2 hours ago, rotorman said: what could cause OP to run high? Is the pump adjustable? Is there anything else in the oil system that could cause high pressure? As a quick check without putting a gauge on it, how much pressure does the electric pump put out? Oil pressure or fuel pressure? Quote
carusoam Posted August 1, 2022 Report Posted August 1, 2022 Things to consider…. 1) Flow of liquid… more gph can generate more pressure, given a few other details being in place…. 2) Increased viscosity of fluid… if the fuel viscosity increased… but it doesn’t discernibly….. 3) Tightened tolerances in the fuel plumbing…. If something is blocking the fuel from flowing, the FuelP is going to go higher…. While the FF gets cut down… 4) Instrument or measuring system error… know that some calibrated dampers may be used with some sensors, that may intentionally include air in the line… make sure air is in the line if it is required…. 5) Some digital FuelP sensors have a computer onboard…. Some of their electronics may fail over time… PP thoughts only, not a mechanic… Best regards, -a- Quote
rotorman Posted August 1, 2022 Author Report Posted August 1, 2022 15 hours ago, Fly Boomer said: Oil pressure or fuel pressure? Sorry. FP fuel pressure. Quote
rotorman Posted August 1, 2022 Author Report Posted August 1, 2022 17 hours ago, PT20J said: The the pump pressure is not adjustable. The fuel pressure should vary inversely to the flow. The highest pressure should be at idle and the lowest pressure should be at rated power. I see the opposite. After landing the fuel pressure drops. Before take off it is lower than in the climb. Then reduces a 1 or 2 psi as climb power is reduced. Quote
rotorman Posted February 27, 2023 Author Report Posted February 27, 2023 (edited) Resolution to the high fuel pressure was a broken wire. I had purchased a new sending unit and gave it to the shop to install during my annual but they found the break and repaired it Edited February 27, 2023 by rotorman misspelled word 3 Quote
M20F Posted February 27, 2023 Report Posted February 27, 2023 21 hours ago, rotorman said: Resolution to the high fuel pressure was a broken wire. I had purchased a new sending unit and gave it to the shop to install during my annual but they found the break and repaired it @PT20J which was the first response is the right response. Easy and cheap first it generally works. Glad it worked out. Quote
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