1991 gmc Sierra 5.7
Since my last oil change my oil
pressure isn't building, it used to sit
on 30psi now it barely reads on the
dial, any advice on the problem?
Well I wouldn't run it until you find the problem. You can try replacing the sending unit. How is the oil level on the dipstick. Did you change it or a shop.
Personally I would check the pump first but I have tools and equipment to do that. To test the oil pressure sending unit I use compressed air and a regulator. Pull the unit out attach the air and plug it back into the truck. Pressure up to a known pressure on a gauge and confirm the reading on the dash. If your sending unit is fine it is either the pump/pressure regulator or engine damage causing the low pressure. Start with the sending unit and we'll go from there.
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