fuel pressure

[erich weaver]

I have 7.5 hours of flight time on my -7A with a IO-360B1B and AFP boost pump. Got most of my initial problems worked out, but one is lingering:

My fuel pressure reading, determined with GRTs sensor and EIS, is usually normal at 27 psi, but occasionally goes erratic for a few seconds at a time. The reading is ALWAYS high for these 2-5 second intervals, but not steady - its bouncing around in the 40-70 psi range before returning back to normal, where it remains rock steady until the next episode. I have not noticed any changes in engine sound or performance during the time of the high fuel pressure readings. It occurs regardless of whether my boost pump is on or off. THis has happened on every flight, usually at least a couple of times over a 45 min.- 1 hr flight. I have noticed that it definitely always occurs near the conclusion of my flights, after I reduce power, slow down, and enter the pattern to land, but sometimes it occurs at other times as well.

I initially suspected that the readings were not real and replaced the sensor, changed the sensor grounding point, and moved the wires a little further away from other wires that were bundled together. No joy there.

I am now suspecting the readings are real and are indicating a brief boiling of fuel somewhere, but I havent heard of anyone else having this problem. I could run a blast tube to the engine driven pump and/or install a heat shield around it and see if that has any effect.

Anybody have this happen to them or have some alternative ideas?

thanks

erich

[airguy]

My first thought is grounding, but you should have taken care of that by changing the ground path.

You might be correct about the fuel getting hot and "flashing" into vapor causing a brief spike in pressure in the line. Do you have an extra OAT sensor you can put on the pump to see what temps you are seeing in this area when the pressure spikes?