Short in EFI fuse circuit when temps went to freezing
 

I realize this might not be 100% specific to my 3.4L swap but I thought I'd start here. My 3.4L swap has been running flawlessly for about a year and 8000 miles. I went through last winter with no issues.

So yesterday temps hit below 20 for the first time this year. I drove to work no issues. At lunch I drove to the post office with no issuse. I left the post office 10 minutes later, started it up, put it in reverse started going and it died. Proceeded to crank but no start. So after a couple trouble shoots I found that the 15a fuse blew. As a temp fix I replaced it with the overhead light 15a fuse and went home. Similar story today and it was even colder when I left work. Blew it again on the first attempt to back out and leave work.

So I obviously have an issue and it seems to be strangely aligned with a quick change to freezing temps. I'm hoping to trace through the circuit tonight and inspect wires but I'm hoping for a little troubleshoot advice either specific to the 3.4L swap as I obviously had to get into many wires or in general on what might trigger a circuit overload or short with the temps changing below freezing.

Thanks in advance for any help!

Well did you figure it out after typing your Post??

Both times it happened you shifted into reverse !!

Not sure what year vehicle you have but does the EFI fuse power the Back up Lights?? Is it indeed the EFI fuse??

I would check the switch for sure. Shorted switch??

The fact it got cold could be unrelated to this fun!!