o2 sensor?
 

so I finally got my car put back together and running, took it out for a test drive and in 4th and 5th gear at about 1500 rpms, if i try to accelerate hard i get a popping kind of sound coming from up front.

my dad talked to a guy at his work and said that he had the same problem. His banks were running too lean/rich on each side and said something about needing to replace the O2 sensor, which he said was about 350 bucks. I looked one up online and it was only about 50, then I heard it HAD to be Motorcraft for some reason.... what do you guys think? and are there any consequences of not getting that fixed right away?

02 sensors as i belive regulate air-fuel ratio. im not sure of any long term effects but having messed up sensors can fool your car in its mpg. my dad had his replaced in his subaru, it was $600.

I would not replace a thing till I knew what was going on and did some tests etc.. Is that car throwing any codes?

I'll be taking it to Schucks today to find out what codes are going off. My check engine light has been on since I bought the car, but I haven't had time or money enough to care. The check engine light recently started flashing, for about a minute and then going solid....for a few mins, flashing.... solid. back and forth. Does the flashing mean its something urgent? cuz it makes it look that way...

When it flashes it means its either a miss fire in the engine or a tranny problem (auto cars only). Gonna take a wild guess and say its a miss fire code. I don't know what schucks is but if they do not read codes for free any other parts stores do now days, minus napa I think they still do not do that.

Thought I'd might add O'reillys doesn't do it either... I used to work for them but I did love the free stuff :D
And the if you hear the popping noise along with the CEL I would agree with spike probably a misfire. I just fixed one in my car and that's what it sounded like a popping noise with the CEL.