Twin whippled 509s. Port motor starts, idles and shifts fine but once you push throttle over 1000 rpm it coughs, sputters and dies instantly or sometimes it may lose rpm down to 3-400, catch itself and slowly come back up to idle. They have new cap, new rotors, swapped fuel pumps, swapped coils and swapped ECMs. They have thrown no trouble codes other than low voltage on the throttle body sensor. Also had the fuel tank drained and cleaned. All fuel filters are clean or new. Any ideas?

I would start by checking fuel pressure

you can pull the IAC and cycle the key on and off to see if its functioning normal..........I had one do similar issues engine would die when put in gear under load, swap the IAC's see if it follows...........what blowers are these 3.3 ?

Fuel pressure 45-50

2.3 whipples

seems high, is that what whipple calls for ? to much fuel pressure injectors wont fire correctly

Think so or so I was told

they'll fire just fine up to 70psi,i tested mine up to 100psi,had to tap start them to fire,but once going,they did fine.I was just testing them to make sure they were fine.

are you talking about the throttle position sensor,,if voltage is low,need to find out what connection is bad.

Yes throttle position sensor

I'd say you have a bad sensor or a sensor ground was missed.