New to the list and need some advise on a problem I'm having with a 96 LT1/4L60E conversion in an 89 FJ62. Computer was reprogrammed and harness gone through by FI spec. in Texas. Motor/Trans installed. I can fire it up, but runs very rough and dies. Used the stock in tank pump and get 45 psi with key on and 35 psi when motor starts. Crimped return line and get 60 psi with key on and 50 psi when running, but still dies. It has the four O2 sensor system and the rear two sensor are just plugged in to the harness and not tied into the exhaust pipe because no exhaust yet just about a foot or two of pipe coming off the manifolds. Could the rear two O2 sensor not being tied into the exhaust be giving the computer an inccorect air/fuel mixture reading or should it still run? This motor ran great in the Camaro it came out of and only has 67k miles. Any advise will be greatly appreciated!!