92 f150 5.8l truck wont start unless I prime with gas in intake. It will then start but run real bad and trans will not shift(starts out in 3rd) check engine light is on. After a couple of seconds sometimes it will stall and instantly starts right back up. Sometimes the light will go off and it runs like a new truck sometimes the light stays on and still runs like crap. Fuel pump never shuts off in either tank. Have tested the modulator and there is no gas in it and getting plenty of vacuum why will it run after priming and why does it sometimes not run right?