The bare facts:
IO-360 stock Lycoming with an Andair boost pump, about 400 hours on the engine
Very, very, very intermittently, I see the fuel pressure drop from a normal 25 or so PSI down to 12-14 PSI, then back up again to normal, over about 2-3 seconds; by intermittent, I mean maybe once every few *months*. This has happened perhaps 5-6 times since the plane first started flying.
I cannot correlate this with boost pump use...it's happened after turning on the pump to switch tanks, then turning it off, BUT it's also happened in straight and level flight, as well as in maneuvering flight.
I cannot correlate this to MAP or RPM, nor to a particular tank (although I'm now collecting data to try to do this).
Vents are rocket-style, coiled lines in the wing root, and appear to be clear (i.e., they're venting just fine, and occasionally belch a little fuel when the tanks are very full and get hot sitting on a ramp, etc.).
I have no working hypothesis to account for this. One which was suggested was some sort of an issue with the bypass valve on the Andair pump, but I don't know how to test this.
Needless to say, the first time this happened, 3 years ago, it got my attention (and the EFIS alarmed); 2nd time, maybe 6 months after that, I was a bit more calm. The last couple of times, over the last 6 months (or thereabouts), I just shrugged and watched it go back to normal, but *obviously* I'd like to find the source of this and fix it.
Open to any and all ideas.
IO-360 stock Lycoming with an Andair boost pump, about 400 hours on the engine
Very, very, very intermittently, I see the fuel pressure drop from a normal 25 or so PSI down to 12-14 PSI, then back up again to normal, over about 2-3 seconds; by intermittent, I mean maybe once every few *months*. This has happened perhaps 5-6 times since the plane first started flying.
I cannot correlate this with boost pump use...it's happened after turning on the pump to switch tanks, then turning it off, BUT it's also happened in straight and level flight, as well as in maneuvering flight.
I cannot correlate this to MAP or RPM, nor to a particular tank (although I'm now collecting data to try to do this).
Vents are rocket-style, coiled lines in the wing root, and appear to be clear (i.e., they're venting just fine, and occasionally belch a little fuel when the tanks are very full and get hot sitting on a ramp, etc.).
I have no working hypothesis to account for this. One which was suggested was some sort of an issue with the bypass valve on the Andair pump, but I don't know how to test this.
Needless to say, the first time this happened, 3 years ago, it got my attention (and the EFIS alarmed); 2nd time, maybe 6 months after that, I was a bit more calm. The last couple of times, over the last 6 months (or thereabouts), I just shrugged and watched it go back to normal, but *obviously* I'd like to find the source of this and fix it.
Open to any and all ideas.