Fuel Pressure fluctuating

[Leaph737]

I have a Aersport I-0360 engine with a Silverhawk Ex-5AV servo and a Dynon Skyview system in my Rv-7A and recently I have noticed that my fuel pressure will start to fluctuate every onece in a while when I go above 5,000 ft. Normally it would remain steady at 24 psi but when I have it leaned out it will fluctuate down to 21 and sometime goes down to 18psi and then stay at 24 for for a while. It is only intermittent. Most of the time time it hangs at 24. I usually cruise at 23 squared. I have changed out the Kavlico sensor to no avail. There are no other indications that lead me to believe there is a lack of fuel. fuel flow is normal and remains steady. I have checked all my fuel connections and they are tight. I only have 230 hours on the engine and I spoke with a Lycoming engine builder and he said the fuel pump should last till overhaul and it is very doubtful it is that. Has anyone ever seen this before or have any suggestions? I will be calling Precision Airmotive and Dynon to see what they have to say.

[brad walton]

I have had a similar problem on my Superior IO-360 with the Silver Hawk fuel injection. My problem only manifested itself when I was flying long cross country for several hours at a time. Never on local flights or two hour flights. My fuel pressure would vary widely from normal of 24 to 26. It would go up to 28 and down to 18. Of course, I thought faulty pressure gauge, faulty fuel pump, faulty EFIS. It was none of those. I have a quarter inch SS braided line going from the fuel pump to a Vans supplied manifold on the firewall. There was a miniscule leak where the fuel pressure sending unit attached to the manifold. So small it only showed very tiny bubbles/foam when sprayed with soapy water and the electric fuel pump used to pressure up the connection. I believe what was happening is pressurized fuel would displace air in the quarter inch fuel pressure line to the manifold through the very small leak and work a hydraulic hammer effect on the sending unit. So if my EFIS had (for example) a one second fuel pressure refresh rate, it would periodically measure the pulse of the fuel pump. If the EFIS fuel pressure refresh occurred on the pump compression stroke it, it would show high pressure. If it happened between strokes, it would show low pressure. When the hose is full of air, it dampens this out. But full of liquid and it shows whatever part of the pump stoke pressure present. Fixed the small air leak and no more problems. It would take me a couple of 4 hour legs to have this occur. I discovered the problem when I disconnected the fuel pressure sending line and found it had an ounce or two of fuel in it. It doesn't take much to fill a quarter inch 18 inch long line. Hope this helps.

[Leaph737]

Brad you are spot on with your adivce and thank you. I just got off the phone with Aerosport Tech and they are pointing me in that direction as well. Guess its time to take the cowls off and pressurize the system and hit it with some soapy water.