I don't use this a lot so hopefully I have the right thread here. Before I start, I do know about jrichker's crank no start checklist. I am running through that, but I wanted to see if anyone here had any ideas aswell (I'm also working for a little bit longer so I have to wait to go back to working on the checklist anyway). I just swapped out a bone stock 5.0L motor to a more well built 5.0. This motor has been rebuilt, GT40 heads, upgraded springs, rockers, explorer intake, 24lb injectors and MAF, aswell as a 75mm TB. This all from a bone stock motor. The issues I'm having is idle problems (believed to be timing, it also has a serious vibration when letting off gas but I think its all timing). Now the real confusing issue.. the car starts right up like a champ when cold, but once it's warmed up if it gets turned off, itll crank and crank but wont start. Here's what I have checked.. spark is confirmed good, definitely have fuel pressure (checked the schrader valve) and I can hear the fuel pump kick on, and I checked all of the grounds. I think it could be the ECT sensor but I'm not sure if it's the wiring or the sensor itself. Im getting a new sensor anyways, but when checking for continuity with a light on the wiring, its very dim. Is this how it's supposed to be? I also ran key on engine off codes and I got code 15. Apparently this could be because the battery was left disconnected for a long period of time and the motor may just need to run for 15-30 minutes to clear it all up? The computer was not messed with at all and worked fine with the last motor so I don't think its bad. I am a little stumped with this, so if anyone has some ideas feel free to chip in. Im going to try and get some more of this checklist done today. Thanks all!