Excess fuel pressure new 914 pumps

Hello – we have just replaced the two Pierburg 7.21440.78.0 fuel pumps on our 914 Eurofox (connected in series with check-valves “around” each pump) as required at 1000hours.

We have a UMA fuel/airbox differential pressure gauge and above 29”Hg with just the main pump running, the pressure is just above the maximum differential of 5.08psi, but climbs well into the red (above 6psi) when the auxiliary pump is switched on.

Below atmospheric pressure, the differential is much higher (up to 7psi) and although the Fuel Pressure Checking and Adjustment e-learning video says this is normal and no cause for concern, this happened to a much lower extent with the old pumps and differential pressure always remained below the maximum of 5.08psi at higher throttle settings above 29”Hg.

The regulator was not adjusted when the original pumps were installed when the aircraft was new so I am reluctant to touch it now.

The old and new pump part numbers are identical. We have changed the check-valves to no effect. Is it possible that one or both of the new pumps is our of spec and delivering more pressure than it should – has this ever been heard of before ?

Thanks for any suggestions !

Mark