Could ground loops cause Serial Input to be erratic?
 

I have an MS Labs MS3 Basic + MSLabs CANBUS Module on a 97 with ODB1 Rewire, and a home made grounding kit w/ 4guage copper wire at
Battery Negative to Chassis (stock location)
Alternator to Chassis (engine bay)
Cylinder Head to Chassis (engine bay)

I think there may be a ground loop cause there's a lot of noise when I use the aux input on my radio with anything charging in the car. i.e. aux connected to phone, phone charging thru car 12v accessory it'll produce a lot of noise and whine when I'm driving.
WB Input through the CAN module is set up properly. It reads correctly 40% of the time in TunerStudio. Sometimes it reads the error amount (set to 14.8) or it'll get stuck on a number. Other times it works flawlessly and updates really fast.

Grounds seem to be the obvious answer. What if I ran the ecu ground directly to the battery would that help? I'm going to remove my grounding kit and see if there's any difference.

Appreciate any input on this Thanks!

I would not ground the alternator to the chassis. That's the biggest noisemaker in the car and should be grounded to the big lump of iron up front through its mounts.

You should also use braid for ground straps, not copper wire. Do you still have the OEM ground straps and are they in good enough shape to re-install?

Hey Hornetball thanks for your feedback. I made a mistake actually I did use braided.
Wire: Stinger Pro Series 4 Gauge Translucent Black Power Wire
Terminal: Install Bay Copper Ring Terminal 4 Gauge

I did not remove any of the old grounding points. I will remove the ground for the alternator and do some testing. Thanks again!

This is the kind of braided wire that should be used for ground strapping:

https://www.amazon.com/Small-Parts-T.../dp/B003R501JU

Thanks Hornetball, I took the home made ground off of the alternator the noise seems to have improved but there's still some. I'm going to return everything to the stock configuration and test for any improvement. After that I think I'll put the ECU and WB on a common ground.

I removed both home made grounds from the engine bay drove it a couple of times and noticed instant reading and consistent during my 2 drives. Will continue driving but this seems to have done the trick!