need help f150
 

<TABLE><TBODY><TR><TD vAlign=top width="100%">i have a 97 f150 4.2l with a 120,000 miles on it. when the truck warms up and sitting at a stop with the brake on i start to loose oil pressure, but when i touch the gas or shift into park it goes right back up, and is soild as a rock. i changed the oil pump and relieve valve.
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My 01 F150, 4.2 has done the same thing for several years. Still don't know what the deal is. Seams to do it more when I'm near due for an oil change.