[G3 Q&A, Help & Troubleshooting] HuffleStumps:
UPDATED METHOD [9/08/2016]

I updated this post after learning a lot from people who posted here(thanks) I was kind of away for a while but now I'm back and had no idea that many people have replied, so sorry for taking so long to update this, but this should have plenty of information (the right kind) and hopefully you're all successful in improving the GPS on the G3 (it's always been flaky for me).

Hi, this is my first major thread / tutorial here on G3 Troubleshooting. I was having issues with GPS since I replaced the entire housing to replace the touchscreen and display so I figured it was an hardware problem.

This is meant for you if you've tried all kinds of roms / kernels and still aren't getting decent GPS reception.

I am not responsible if you damage your own phone by doing something stupid. Do as I say at your own risk. Stop reading if you don't understand this.

NEW METHOD

The main part responsible for GPS reception on the G3 is the little board that serves as an antenna on the lower part of the phone, left of the usb port. "According to the service manual (page 139; paragraph 3.9.2) GPS antenna should be connected to the two contacts near upper left corner of backside of the mainboard (up and to the right from TP1 ). According to the service manual, post mentioned by [MENTION=6206580]SIPHOR3ON[/MENTION] makes perfect sense." - [MENTION=4234598]DavisNT[/MENTION]

This is the right answer.

Start by disassembling your phone following any popular guide on youtube. Stop when the main board is fully removed.

This is the old "fix". It can improve cellular reception (probably won't) but it won't hurt performance either:

Some photos by [MENTION=2686348]UvarovG[/MENTION] (Make sure to thank him!)

http://xdaforums.com/showpost.php?p=68587899&postcount=11

I don't think this is worth doing at this point, but if you wan't, the photos are there...

The real solution, as pointed out by both [MENTION=6206580]SIPHOR3ON[/MENTION] and [MENTION=4234598]DavisNT[/MENTION] (You both are right), is to lift up the pins slightly on the two contacts near upper left corner of backside of the mainboard (up and to the right from TP1 ). You should also scratch the pads that the pins make contact with SLIGHTLY with something abrasive (this is optional). I would also lift up the two TINY pins on the little board near the micro USB port (the board I mention in the OLD tutorial that I scratched off).

Photos of the NEW Method (External Post)

Check out this post by http://xdaforums.com/showpost.php?p=66294079&postcount=6 by [MENTION=4512619]gbb14[/MENTION] he has some photos and explains how to do the NEW method (the one that actually improves GPS performance)

MY RESULTS

Indoors:​

Before - No fix / No signals | After - 6 satellites with medium SNR and a fix after 5 seconds; Acc: 10m

Outdoors:​

Before - Fix after 10 seconds / losing signal while in a car or cities with big buildings | After: Fix in 3 seconds; 10+ satellites; acc: 3m best, 4-5m average

This was MY EXPERIENCE. I really believe that if your antenna for one reason or another is going flaky, this should at least improve it.

I learned a lot from this, but take this with a grain of salt, results may vary.

Thanks for reading and hope you get good results :)