Fuel pressure tests should be done with the engine not running, ColdDna - to 36 +/- a tad. With engine running; manifold vacuum influences pressure, and there is no specs for that. Recheck pressure in ‘D’.
However, 28 psi rail pressure with the engine running is not abnormal. No specs are given for pump current, and your ‘0,57A’ seems low - but 7 - 10 A indicates a stalled pump. Pump stuck in debris, or whatever; usually the pump will ‘harmlessly’ chew up particles that passes the in-tank filters. Pump may be worn and sticking…?
To test pump itself; connect pressure gauge to rail inlet hose to check ‘raw’ pump pressure. If the pump runs; it should show 100+ psi (‘new’) - below 40 psi it will not sustain all engine demands. Generally; if the pressure is below some 60 to 70 psi - change the pump…
If the pump is intermittently stalling; the cause should be investigated - if stuck in debris, clean up. If ‘raw’ pressure is low; the problem is the pump itself - but if it continuously ‘chews the cud’, it wears over time, and cruds up the filter…
xj6 85 Sov Europe (UK/NZ)