Fluctuating fuel pressure at high OAT's

[mistergerf]

I've noticed fluctuating fuel pressures recently. I'm fairly sure that its related to ops in high OATs. Here are the symptoms:

Normal fuel PSI is around 26 psi - pretty solid indication the majority of the time. At high OATs I first notice that the decimal on the psi readout starts flickering up and down a few tenths. Then I start noticing pressure excursions down as low as 11 psi for 5 to 10 seconds and then recovering to about 24 psi and then continued flickering of the tenths with the occasional excursion. No change in engine power during flight although I do notice some engine surging on the ground, at my destination, ranging from 800 to 1,100 RPM.

Am I looking at fuel vaporizing in the lines ?
What are my options for preventing this ?

(Here are the tech details:
AF2500 engine monitor. Standard Vans fuel pressure manifold on the forward side of the firewall connected to the mechanical fuel pump. Aerosport IO-320 D1A, AFP fuel injection with purge valve and HP fuel pump filter on the cabin floor (not running). Fuel lines FW forward are all sleeved with the orange stuff. OAT ~ 90 deg F. CHTs 375 - 405, EGTs ~1,300, oil temp ~ 205, 65% power. Basically nothing is red-lining, even the fuel PSI is within tollerances... but ...)

Any thoughts, panic warnings, suggestions ... ?

Gerry.
(N696WG, RV-9, 145 hours)

[Jamie]

Hi Gerry:

Just a couple of things come to mind. I'm not sure about the AF2500, but on my Dynon if I disconnect the lead on the pressure transducer my fuel pressure pegs to the high end. I would double-check to make sure you're getting a good ground on the pressure transducer. A friend of mine was having erratic readings for this very reason.

I'm assuming you have a fuel flow transducer installed. Where is it in relation to the fuel pressure transducer? The floscan transducer has a tiny orifice which can agitate a vapor situation if it is upstream from a pump.

[dan]

Gerf,

I see the same thing from time to time, more often in the summertime.

[mistergerf]

Jamie, my fuel flow sensor is between the fuel meter and the flow divider, so shouldn't have any bearing on the pressure transducer. I'm pretty confident the transducer is functioning since I only see this at high OATs. The transducer wiring is factory at the transducer - my wiring for the ground is at the analog unit which is inside the cabin.