moyassine

The other day we installed a new built 2.0 long rod in my car and got it all fired up on the dyno. Once we started tuning we had a sputter/backfire starting around 2krpms and clears up after 4k rpms. So I took the car home and started diagnosing it two days later and I still couldn't find any bad sensor or electric problem. So I started swapping sensors since I had all of them laying around. Started with cam sensor. Then crank sensor. Then knock sensor. Then tps. Only thing I didnt replace is the map sensor since its reading fine and what not. Problem still occurred. So I went ahead and replaced the whole engine harness because at one point I had code for knock sensor high voltage and tps high voltage. So I thought it's a ground or a short in the wiring. We tried new plugs. And I have a cdi box. We tried different ignition qnd the car still sputters at 2k. Also one of my fuel pumps went out. (I had a surge tank) so I redid the whole fuel system with two walbro hellcats Intank. Any help would be appreciated. Timing is spot on. Fic 2150s recently cleaned and flow tested.