Custom CAN/GPS/Oil Pressure Sensor Powering Issue

Hello,

I am intending on making a custom CCA that will extract CAN from the Car, oil pressure measurements, and have a GPS receiver collecting data, all to be sent over bluetooth to my phone for RaceChrono. For background I am using the ASC connector on the GR86. See this for more information: https://github.com/timurrrr/ft86/blob/main/can_bus/gen2.md.

On the bench, using a linear power supply at 12v, I can successfully power all modules at proper power levels and wrote the esp32 firmware to functionally work. I get GPS NMEA, CAN messages with USB tx/rx dummy, and analog sensor measurements from my AWG properly shown in the app.

However, when I actually use the car everything seemingly has power, but it does not work. The 5v line is more like 4.5v, sometimes it even oscillates between 3.3v and 4.5v. The gps has proper power but is not getting fixes despite being outside (works on bench in a closet indoors), the CAN system works sometimes but sometimes does not, and the oil pressure sensor does not work at all.

I am sort of at my wits end with this and am debating just fabbing the board since I suspect this is a power/noise/grounding issue which may be easier resolved on a PCB instead of a bunch of breadboard wires in a 3d printed enclosure.

What I don't get is how it works fine on the bench but not at all in the car. The grounds are all common to that of the esp32 breakout board and the only thing changing between the cars is using the real male connector instead of the test one I made so I can stimulate power and CAN with usb and power supply.

Any insight would be greatly appreciated. Attached is my 'functional diagram', the 'formal' schematic with my test setup (likely has errors), and the physical layout. The part with the connector includes a fuse, TVS, and shottky diode in line, all of which works fine on bench.

Here are the associated part numbers:

Oil pressure sensor - MIPAN2XX150PSAAX

Metripack sensor connector - 734-1164-ND

ASC connector - A142498-ND

ASC Connector 2 - A106550-ND

GPS board - 1528-1272-ND

Buck - 1738-DFR1015-ND

Fuse holder - F8428-ND

ESP32 - FNK0060B

ESP32 BoB - FNK0091

CAN receiver - Waveshare SN65HVD230

Again, any insight would be amazing, thanks

Duplicate -- sorry