Greetings all!
Need some help with a starting issue. About three weeks ago I went out to start my SC400('92) and it would crank but not fire. Thought it might be the fuel pump or fuel ECU...replaced both items...no luck. I did manage to create a "hot wire" at the EFI relay...started right up. Long story short...replaced the main ECU...bingo...started right up, but only lasted 3 days.
Got stuck again...same symptoms...crank but no fire. Once again the "hot wire " at the relay saved my ***. When I removed the relay it was very hot to the touch...don't know if that is normal or means anything.
All thoughts on this subject will be greatly appreciated...hope I didn't damage another ECU!
During this entire process I managed to create a hot wire at the relay

 

try bypassing the fuel pump ecu first. you may have replaced with a faulty unit. did you replace the fuel pump relay?

 

Ive had almost this same problem on my '93 Sc400. I replaced my Fuel Pressure Regulator and it's firing up just fine now.