[Samsung Epic 4G Touch] Adreaver:
Revamped the entire OP to make it relevant for current roms.

Many users of the Epic 4g Touch have reported various GPS inconsistencies. While this seems to happen more frequently on AOSP-based ROMs (CyanogenMOD, PAC-man, Evervolv, AOKP, etc), it has been reported on TouchWiz-based ROMs as well. Below are a few tips and tricks to help fix your GPS.

FIRST: You will need the necessary tools to troubleshoot the problem.

Google Maps - The app we will use to determine if GPS works properly or not.

GPS Status (Optional) - Provides additional information about GPS performance. This shows how many satellites are in view, coordinates, heading, and other useful information as well. This can help to confirm wether you have a GPS problem or are just in an area without GPS reception.

SECOND: You will need the tools to fix the problem.

- Root-capable file browser (ES File Explorer is my personal preference)

- Mobile ODIN (Free version is available on XDA, but Pro is well worth it, as well as supporting Chainfire, one of the most respected devs in the Android community)

THIRD: You will need some files saved to your sd card. These will be flashed in recovery or Mobile ODIN.

- The EL26+CWM recovery kernel.

- Any Jellybean ROM you want to run.

***For TouchWiz ONLY* Agat's 0.3.0 GB27 Kernel with tREC custom recovery.

- A working GPS.conf (explained later)

- Goddly's ComaDose tweaks (not required if you use a standalone GPS.conf, but highly recommended. See his thread for details.)

FOURTH: You will need these files on your sdcard to temporarily return to stock if needed.

- The EL29 CWM5 Directboot Kernel

- The EL29 Tempboot ROM

METHODS:

I will post each method of fixing GPS, in order of time investment. Test GPS with Google Maps (and optionally GPS Status) after EACH METHOD. Please provide feedback on which method worked for you so that I may improve this guide further.

Method 1 - GPS Toggle

Try this first. It only takes about 10 clicks to do the whole thing, and it saves you from having to flash anything if it works.

1. Close Maps and any other location aware apps. Make sure to clear them from Recents to ensure that they are fully closed.

2. Go the your Location tab under Settings. Toggle GPS satellites off and on, then toggle Location as well (System Settings>Location Access>Access to my Location). This should result in a popup asking if apps can have your permission to use GPS.

Method 2 - New GPS.conf

All thanks to Goddly for allowing me to use his gps.conf.

Sometimes, the GPS.conf file on your phone can become corrupted or otherwise unusable. This will prevent you from locking on to any satellites, even though you may have one (or several) in view.

1. Make sure you have a working GPS.conf on your phone. This can be a standalone GPS.conf like the one attached to this post (extract the zip first!), or it can be one contained in a tweak package such as Goddly's ComaDose v1.4

2. Copy & paste the working gps.conf into /System/App using your root file browser.

3. Set permissions to the gps.conf to 0777 (rwxrwxrwx)

4. Reboot.

5. After booting, toggle Location (triggering the popup).

Method 3 - Lock on Stock

This is a tried-and-true method that was most frequently used in the early days of CM10. It is usually not needed anymore, but I am keeping it in just in case.

1. In Mobile ODIN, flash the EL29 CWM5 Directboot kernel.

2. Reboot, you should automatically wind up in recovery. If you do not go to recovery, pull the battery, wait 10-15 seconds, replace the battery, and hold vol+ and power.

3. Flash the EL29 Tempboot ROM (This will be in the Multiboot folder on your SD card, assuming you followed the instructions in the link above.)

4. You should automatically boot into stock EL29 Gingerbread.

(Optional) 4 1/2. Update Profile and PRL (if desired, you can't do this on AOSP so you might as well do it now)

5. Open Google Maps and get a GPS lock (you will likely need to be outside to get a good lock). Sometimes it helps to navigate to a random place.

6. ***WHILE YOU STILL HAVE A GPS LOCK***, power down the phone, then hold vol+ and power until you boot to recovery.

7. In recovery, Wipe Cache, Wipe Dalvik Cache.

8. Flash your ROM of choice.

9. Reboot.

Please reply to this thread with any questions/issues/feedback.