* Oil Pressure: This varies with engine speed and temperature. A cold engine will have higher pressure than a warmed-up one. A normal operating range is typically between 10 and 50 PSI at idle and 30-60 PSI at higher RPMs. However, the exact specification will be in your owner's manual. Anything significantly outside that range warrants investigation.
* Fuel Pressure: This is also variable and depends on engine load and speed. It's regulated by a fuel pressure regulator. You'd need a fuel pressure gauge to measure it, and the specification will be in your repair manual or from a parts supplier. It's much higher than oil pressure.
* Tire Pressure: This is completely separate and depends on the tire size and the recommended inflation pressure found on a sticker inside your driver's side door jamb or in your owner's manual. It's typically expressed in PSI (pounds per square inch).
To find the correct PSI, you need to specify *which* pressure you're interested in and consult your owner's manual or a reliable repair manual for that year and model vehicle.
