1999 Ford Crown Victoria troubleshooting

My 1999 crown Vic is the best car i ever had,but now i facing difficulties, its a V8 with a 4.6 its a x state car, highway patrol i think its the P51. my car was running great i had just got in town ,before i was speeding about 90 miles per hour ,so forth i got in to town and the car was running great.I seen my grandmother and she waved me down ,so i stopped .she asked me to do something and i said OK .so when took off i squealed the tire,not crazy but did,and then i herd a knocking sound so i slowed down and listen ,i went to turn around and the knocking was gone but then it stared missing.i changed the oil and filter come to find out that i was 2 and a half quarts low. so i checked the spark plug but it was fine so i check the the coil,but it was fine,and then i check the injector,but that was fine too..the car is not knocking anymore,so then i checked the compression,and fine..its the four piston that is missing and i cant find out why, can u guys help me i think this is a very good one for you guys thank you for any help you give me yours truly gerry P.S the knocking was about 15 seconds and the just missing and still missing no knocking thank you