1999 Ford F 150 W4 6 V8 Wean Hit Gas Oil Pressure Normal Break Empty Checked

i have a 1999 ford f-150 with a w4.6 v8. wean i hit the gas my oil pressure says its normal but wean i hit the break it says its empty. i checked the oil and the water there both full. i done a oil change to make sure there is no water in the oil and the was no water in my oil. my truck dont run hot or smoke but it just started to knock. i thought it might be the oil pump but im not sure.