Oil Pump

Good news, yes there is a spring that can be shimmed to increase the oil pressure or put a weaker spring in to lower the pressure.

Bad news, you have to drop the oil pan to get to it. The oil pump can then be taken off the main bearing cap and taken apart. There is a pin holding the spring in, that has to be driven out. While you have the spring out you may as well pull the relief valve out and clean it, chances are you have dirt in the relief valve, if the problem is truly the oil pump. The other reason for low pressure is worn bearings.

Hope this helps!

Thanks that's what I thought. I replaced it with a new pump and the pressure is 50psi instead of 40psi when the engine is warm.