What about fuel flow readings?
Not being sure that my skin is as thick as Sam B's, I throw in a few observations anyway.
First off, in a former life at GM-Pontiac, we learned that vapor pressure of fuel increases with temp, altitude, and octane. In the mid 80's, we had vapor lock issues particularly with the Firebird 5.0L, carb and later FI, that would actually cause the car to run rough at altitude on a hot day, eg Tahoe/Denver in the Summer, or be difficult to restart at all. On the carb model, could actually smell fuel vapor if it had been sitting for a few minutes shutoff, hi alt/temp. Fuel lines would get hot, especially fuel injection lines to injectors, and boil fuel inside, etc.. Precisely metered FI systems and injectors, carbs with throttle body injectors, or float type did not like that, for various reasons.
With airplanes we have all the same conditions present, i.e. even higher octane, altitude, temps. Recipe for vapor lock. Remember that in a pressure reading situation, vapor/air is far more compressible than fuel, so if vapor is acting on the FP sensor, not as much pressure will be sensed, assuming sensor is working as designed. And if the fuel pressure sensor happens to be at the highest point of the system, well there you have it, especially if you've ever tried to keep the air bled out of that high up oil pressure line/sensor, avoid that few second wait for oil pressure at start up. If you say well how does air get in the closed fuel system prior to the engine pump or sensor, consider how a diver gets the bends fm nitrogen bubbles forming in a closed blood circulatory system. I'll defer here to the chemical engineers and the seasoned SCUBA divers among us.
In climb vs level flight, angle of air entering AND exiting cowling changes, as does flow rate. In fact, the flow pattern in the engine compartment could very well change. This goes to cooling of fuel pumps, sensors, cylinders, anything under cowling. With a C/S prop, prop pitch changes also change air flow.
Since we can't really control altitude or octane, and if this is a vapor lock issue, cooling is left, with one caveat, pressure on the supply side of the system. More pressure on the supply side, especially at higher FF/power settings tends to alleviate vapor lock in many applications, i.e. at the FP sensor. If the engine mechanical pump is demanding more flow, it tends to put more suction on the supply side, better chance of forming vapor bubbles somewhere, i.e. FP sensor. This is alleviated somewhat by an electric (pre) boost pump.
But getting to MY question, for those with fuel flow and fuel pressure sensors co-located, what is the fuel flow doing while the fuel pressure is fluctuating? In my case, this fluctuating reading issue is definitely better after just refueling on a cool day (i.e. fuel farm tank fuel is cooler), and worse in climbs, and especially if doing a lot of pattern work with prop at lower/flatter pitch settings, higher deck angles.
Here it's an O-360 with C/S prop, VM1000 system (early), and with a prior history of a fuel flow sensor swap to no avail. Fuel pressure sensor has never been swapped out to my knowledge. Boost pump off, FP can be anywhere from near zero to 5 psi. Boost pump on, always an increase, max 6 psi. Now fuel flow, that has a mind of its own. Only other comment is that my fuel line takes a 90 degree turn a little sooner after the FF/FP sensor manifold than might be ideal. A no-no at least with my swimming pool water flow sensor, flow disruption, etc..
Thanks to all that risk abuse by giving answers.