I put a 1996 4.6 engine and ecu wiring into a 1991 mustang. I made a custom harness to connect the 96 ecu harness to the 91 car harness and added the diagnostic port. the fuel pump primes and the car starts, and then stalls after about 1 sec of running. If I try to restart it it just spins over. If I turn it to the off position it starts right back up. I had a custom tune and the pats turned off on my ecu but it still does the same thing. All the gauges work tach, oil pressure, alt, and water temp. I also used the fuel tank and lines from the 96.

SOURCE: 66 mustang engine running out of fuel

Do you have any of you fuel lines close to the exhaust? (vapor lock)

SOURCE: 1996 Ford Windstar engine runs rough

DIS ignition, no distributor to " get in there " with....

SOURCE: I have a 87 ford

the ecu is located on the passenger side under the dash along the kick panel.the connector for the ecu is under the hood on the same side and it is held to the ecu that sticks out a little with a single bolt.this system used an 90 wire plug,and is bolted to the firewall with 2 bolts.

SOURCE: 4.9L straight six: Hard start when cold, black

Considering the regulator has no effect on starting lets save that for later. You are surely getting too much fuel. Try unplugging the TPS (hot, cold, and startup). The computer will substitute a default value and you will notice a difference if it's as bad as you say.