Hi can anyone help with this please!?!?
 

i have a 1988 gt. when i got it, it had been sitting for 3 years or so. but indoors.
Anyways, I replaced fuel lines, fuel pump, fuel filter dis. egn. plugs wires did a major tune up new mas air sensor and cone filter. she ran really good was out of time a little but got it timed and set idl. Now here is the problem last week it would start drive for about 3-4 mins and shut down. and would just turn over but wouldn't start. I would let it sit for a few hours and it would fire right up. i let it run for about an hour just sitting in park. So i thought it might have been fuel pressure reg so i changed it. still did it. So i found out it was the Nersua Switch in the trunk so i replaced it. When i replaced it i did what the directions told me to do disconnected the neg batt term and installed switch. It fixed my problem. But now i will start my car and it will be fine ill run it drive it its good.
but when i turn it off and start it again it will ideal nice and as soon as i rev it it pops and cracks out of the drivers exhaust about mid way i have duel chamber flowmasters i cut the back cats out but ive done that with previous stangs never been a problem for me. When it pops its not when winding down or being cold. It dose it every other start up it seems like and it sounds nasty not a good pop sounds the same as a built 302 winding down from high rev kinda like a back fire but a lil nastyer i.d.k ive checked almost everything and cant figure it if anyone has any ideas or input it would be nice and appreciated Thanks.