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!
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