Some context: I drove the car for a half hour this morning, no problems at all. Parked it. 15 minutes later the fuel pump stopped priming.

Here's what I found and what I tried:
Cleaned the following grounds even though they were already clean for the most part- battery ground, transmission ground, thermostat housing ground. The only ones I didn't clean were the valve cover & alternator ground but I'm pretty sure they're clean as well.
Checked my ecu fuse under the hood, its fine. Checked fuses 24 and 31 under the dash, they're good too.
I hooked up my multimeter to the fuse box & checked for voltage on fuse 24 and 31. With the key in the on position, I get 12 volts from fuse slot 24. Fuse slot 31 has nothing..
I popped open the cover above the fuel pump, hit the plugs with brake cleaner because they were a bit dirty. But I still have the same problem.

Another thing I found was one of the brown wires that are grounded to the thermostat housing came disconnected. I don't have the tools to fix this properly right now so what I did was stripped the wire back, I cleaned the surface of the connector and I had vice grips holding the wire onto ground. I figured this should work just to see if that's my problem but the fuel pump still isn't priming.

The car cranks over & fires up on the remaining fuel in the cylinders but it won't run for more than 2-3 seconds without the fuel pump working. I'm hoping I don't have to replace the ECU so I'm here looking for pointers. I don't even have a spare ECU to see if that's my problem.

Also when I turn the key, CEL comes on as usual, and once it goes out ~2 seconds later I can hear the relay click.

Pictures of the wire that separated from the thermostat housing, as well as my hacky fix just to see if thats my problem: https://imgur.com/a/M2D9uhD

Thanks in advance for your help guys.

 

Sounds like the fuel pump is failing.

 

That's what I'm hoping is the case. But I'm not sure why I don't get voltage from fuse slot 31. Appreciate your words though.

 

Try switching your fuel pump relay with another relay that's the same

 

Apparently the "back up (radio)" fuse under the hood is for the fuel pump too, but that fuse is fine. I was reading about it here: https://www.nthefastlane.com/car-cra...-start-no-fuel

And then there's a main relay but I don't have a spare one to test right now. I guess I'll get that ordered, hopefully it's either that or the fuel pump itself.

 

Solved but for how long I don't know. I pulled the positive terminal off the battery and let it hang for a minute. Put it back on and the pump is priming again.

 

Saw you said you checked grounds on engine area, more work to tear apart interior but there's 3 grounds on the main harness inside the cabin not sure if you've checked those?

 

I didn't check those but I'll see if I can locate them. Thanks!

 

Do you have a hatch/coupe or a sedan? I can tell you where they're located. 👍

 

There is 3 on each, two are in the same place left kick panel and left side of drivers seat behind front left bolt.

Third on HB is under the rear body trim, sedan the 3rd one is on the top shelf/package tray area behind rear seat.

 

Definitely could be the main relay. They are notorious for dry soldered joints which can cause intermittent problems. Easy to fix with even the smallest amount of experience.

 

Yeah I've been looking at this too but mine looks great, it was replaced a couple years ago. Previously this was solved by pulling the positive battery terminal, let it sit for a minute and after hooking it back up everything started working again. Its been fine up until today. So if you check the pictures one of the ground wires on the thermostat housing came off, the car has been running fine without that but all of a sudden the fuel pump didn't prime with it disconnected. I ended up fixing that and its priming again.

It's also worth mentioning my car uses a jumper harness since it has an OBD2 harness and a OBD1 ECU. These jumper harnesses suck. If they move slightly and it completely changes how the car runs, if it runs at all.. So I can't wait to get rid of it. I have a rywire harness that isn't installed yet, I'm just waiting for a couple adapter harnesses from rywire so that it can button up to my setup.