1991f150jason

hey guys i tried searching everywhere for help on this problem but i couldnt find anything.
heres the problem - in the morning the truck wouldnt start. fuel pump wouldnt come on. then it did and the truck ran then shut right back off. after it warmed up a little bit in the day the truck started and ran just fine like normal but this would happen every morning. then my fuel pump just wouldnt come on a few days later no matter what time in the day.
so i ordered the full assembly and dropped the tank and replaced the fuel pump. they gave me a pump with a broken floater(figured that out after the full install) so i was just gonna go off mileage since i didnt feel like dropping the tank again and i needed the truck. ran great and solid for about a day and now it wont come on again. fuel pump relay has already been replaced a few days ago, but still nothing. im getting 12 V to the fuel pump. and im stuck as to why the fuel pump isnt coming on. faulty fuel pump maybe??? please any help would be great.
P.S - the truck has been idling up and down pretty bad while sitting in park or neutral or in drive with my foot off the gas.
ANY help with any of this would be great!!! thank you guys

ive already replaced ignition control module on the side of the distributor and the ignition coil for ignition problems, but that has nothing to do with the fuel pump not coming on but just thought i would add that

VickMacky

Have you checked for any codes yet?

1991f150jason

nope. have not. i have the haynes book that i can check with. what should i look for? never used a code reader. done just about everything else except that.