Diagnose these issues- separate or same

[GrandSport]

So timeline:

Car is track only. After running hard it will hard start. But it always started so nbd.

Engine rebuilt. No issues

Later starts having battery drain. Fast. 3 hours and it's too low to start. One time I swore I heard an electrical humming on the lift, but I couldn't investigate much as I was in a rush. I didn't really care much because I was about to install a kill switch.

2 weeks ago, while idling in hot pits, it dies wont start. Seemed like battery was low, but then even with a jump box, it wouldn't start. Definitely felt like no fuel and got Code P0087. 1/3 tank of gas (and based on normal usage, I definitely had more left in the tank). Tow to garage. Add 1 gallon of gas and starts right up! Weird. Go to fill it up and it only takes 8 gallons. Weird. No problems all day.

Next week, go back to the track. Starts right up (on battery tender). Back up, about to let it warm up and it stalls again. Wont start up again. UGh. Run a different car all day, come back and the battery is super low as expected. Gets to one "click". Push it in the garage and notice clicking coming from fuse box under the hood. Remove key and it stops.

I ordered a new fuel pump (it has an aftermarket one in there)

Engine wise, it's stock aside from CAI/Exhausts/Headers/Tune. No power adders or anything. I unplugged everything aftermarket I can think of (which is really just data loggers).

Fuel pump + unrelated battery draw?
Cam position sensor + unrelated battery draw?
Other? All 3?

[FR-S2GT86]

Originally Posted by GrandSport

So timeline:

Car is track only. After running hard it will hard start. But it always started so nbd.

Engine rebuilt. No issues

Later starts having battery drain. Fast. 3 hours and it's too low to start. One time I swore I heard an electrical humming on the lift, but I couldn't investigate much as I was in a rush. I didn't really care much because I was about to install a kill switch.

2 weeks ago, while idling in hot pits, it dies wont start. Seemed like battery was low, but then even with a jump box, it wouldn't start. Definitely felt like no fuel and got Code P0087. 1/3 tank of gas (and based on normal usage, I definitely had more left in the tank). Tow to garage. Add 1 gallon of gas and starts right up! Weird. Go to fill it up and it only takes 8 gallons. Weird. No problems all day.

Next week, go back to the track. Starts right up (on battery tender). Back up, about to let it warm up and it stalls again. Wont start up again. UGh. Run a different car all day, come back and the battery is super low as expected. Gets to one "click". Push it in the garage and notice clicking coming from fuse box under the hood. Remove key and it stops.

I ordered a new fuel pump (it has an aftermarket one in there)

Engine wise, it's stock aside from CAI/Exhausts/Headers/Tune. No power adders or anything. I unplugged everything aftermarket I can think of (which is really just data loggers).

Fuel pump + unrelated battery draw?
Cam position sensor + unrelated battery draw?
Other? All 3?

You have not mentioned anything about voltage readings. It's very difficult to diagnose vehicle electric systems without the proper tools. Have you been taking any voltage readings with your multimeter? What are the voltages at the lead battery posts and then at the clamps connected to each post while you are experiencing the problems described?

[Lantanafrs2]

I would start with alternator and battery. Motor rebuilt? Maybe there's a ground hanging off somewhere? If there's a draw, get a voltmeter on it and start pulling fuses.

[GrandSport]

I didn't see any loose grounds, but i'll look for them. I'll also get a voltage reading next time I go up the track.
Is there a diagram/schematic of all the grounds?

[Grady]

As with anything electrical get a volt meter and start checking where you are losing voltage.