7MGE oil pressure

[Arne (Denmark)]

Hi there. My first time here.

I have a 1987 MKiii Supra (7MGE) which I bought three months ago.
I topped up the oil with some Mobil 10W40 oil even though the guy I bought it from said I should use 15W-40, because the mileage is about 250.000 km
.
The problem is that after that the oil pressure has tuned down quite a bit. Normally the pressure idling was 1.7 kg/cm3.
Now I can hardly get the pressure to rise to more than 2.0 and it's generally too low. -Only about 1.0 idling.
AND there is a rattling, knocking from the engine!? Nothing when it's idling but gets bad about 2000-3000 rpm. Hmmmm.

Have you guys ever had or heard an oil pump go bad?
What is your normal oil pressure reading on the cars?
Can a faulty bearing cause the oil pressure to fall?

After all I hope it is only my oil pump otherwise I got to look around for another engine.

I will be happy for your comments.