my mazda B2600I spontaniously started blowing oil out of the filler cap knocking as no oil pressure and stalled when allowed to come to an idle.. when i checked the dip stick it indicated no oil so in order to start figuringing out a cause i added 1 qt of oil. the truck had sat for about 45 mins.before i did this. i then rechecked the level and it was overfull. we started it and it ran normally while we drove it onto a trailer to transport it to a shop where we drove it off the trailer. while it was still idiling i removed the oil filler cap and got a rather loud blowback sound and pressure out of the filler hole. any ideas as what to look for probable cause

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1992 Mazda B2600I 2.6l