Make sure the oil level in crankcase is full as well as the HPOP res and the oil psi gauge on dash shows oil pressure. There could be debris in the IPR cavity even though you replaced IPR
To isolate the heads as a potential large leak: 1) Remove the line from the right head and cap with a suitable plug. 2) Remove the left-hand line and connect an oil pressure gauge capable of reading 3,000 psi or greater to it. 3) Crank the engine while watching the gauge for actual pressure. If the reading is low, the problem lies in the high-pressure pump or the IPR. But to determine which is the guilty culprit, you first need to replace the IPR to evaluate. If that doesn't correct it, the pump will need replacing.
IPR pump can go bad / not unherd of. Also I have seen where the HPOP was installed and the gear was not installed correctly and caused low HPOP
To isolate the heads as a potential large leak: 1) Remove the line from the right head and cap with a suitable plug. 2) Remove the left-hand line and connect an oil pressure gauge capable of reading 3,000 psi or greater to it. 3) Crank the engine while watching the gauge for actual pressure. If the reading is low, the problem lies in the high-pressure pump or the IPR. But to determine which is the guilty culprit, you first need to replace the IPR to evaluate. If that doesn't correct it, the pump will need replacing.
IPR pump can go bad / not unherd of. Also I have seen where the HPOP was installed and the gear was not installed correctly and caused low HPOP
