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Getting Started

Requirements

Warning

It is recommend to mod Gran Turismo 4 Online Public Beta as opposed to retail, as retail uses dual-layer discs which cannot be built easily.

Extracting ISO

Refer to the ISO Extraction/Building guide first.

Extracting the game

All PS2 GT titles use the volume system, which will need to be extracted in order to gain access to game contents.

If you haven't already, extract the .iso file using 7-Zip or by any other means. You should be able to see a GT4.VOL file.

Using GT4FS, extract the volume file as such

Extracting GT4.VOL
GT4FS extract -r GT4.VOL

This may take a while, but when complete, you should be able to see a new extracted folder that follows this file structure.

Warning

This section currently only applies to GT4 Online US (SCUS-97436).

HostFS is a feature normally available on PS2 devkits which allows loading files loose without a volume file. This avoids the need of normally creating a new volume file and ISO file for every change you want to make.

PCSX2 supports HostFS, but games needs to have explicit support for it.

As of 30/09/2023 it is possible to patch GT4 to implement and use HostFS thanks to Nenkai.

Requirements

Tip

Ensure that you have the volume extracted into a VOL_extract folder, next to the ISO file before starting this section.

Creating a patched executable

First, use PDTools.GT4ElfBuilderTool to decrypt and decompress CORE.GT4 into its own game executable.

Converting CORE.GT4
PDTools.GT4ElfBuilderTool.exe CORE.GT4 BASE_SCUS_974.36

Then, use PS2 Plugin Injector to inject GT4Hook.elf into the game executable as such:

Injecting GT4Hook.elf
ps2plugininjector.exe -i GT4Hook.elf -o SCUS_974.36.elf BASE_SCUS_974.36

You should now have a file named SCUS_974.36.elf. Make sure that it sits next to the main game ISO.

Setting up PCSX2

QT PCSX2

  1. Add search directory to the ELF file
  2. Actually rename the elf file to have the elf extension to show up i.e SCUS_974.36.elf
  3. Right click on the elf entry, properties
  4. Summary -> Disc Path -> Browse -> Select ISO file
  5. Emulation -> Tick "Enable Host Filesystem"

Non-QT PCSX2

Select your ISO file

  • CDVD -> ISO Selector -> ...

Then, boot through the ELF file (important!)

  • System -> Run ELF... -> SCUS_974.36 (example)

If the game boots, you are good to go and can begin editing files.

Warning

Almost every file should now be available to edit loose, but there are exceptions; you can not edit streamed files such as:

  • pss files (videos)
  • es files
  • sqt files
  • ins files
  • ads files
  • Anything in carsound

These sound/movie files needs to be streamed from the PS2 IOP, they will be specifically loaded from the volume still. Build a volume if you need to edit any.

Additionally, the SpecDB is fully loaded at boot, you will need to restart if you are making any changes there.

Packing a volume

Note

Only use the following sections if you are not using HostFS, if you're making sound modifications, or publishing a mod.

After making edits to game files, you'll need to repack the volume. There are two ways described below, the first being the most convenient.

Method 1 - Appending to the volume

You can "pack" a new volume containing your new content by appending the changes to your existing volume. This avoids having to wait for a full VOL build for what may only be a few changed files.

You would need to create a new folder with the edited files, while preserving the original paths. An example:

Packing Example

.
├─ MyMod/ # Always preserve game paths
│  └─ rtext/
│     └─ US.rt2
│
├─ GT4.VOL
├─ GT4FS.exe
...

Using GT4FS, you would then run the following command:

Appending to the Volume
GT4FS pack-append --read GT4.VOL --append MyMod

Warning

Make a backup of your original volume file. It will be edited.

Method 2 - Building a brand new volume

This is the slow method, building an entirely new volume from an extracted folder.

Using GT4FS, you can run the following command to build a volume from a game directory:

Building a brand new volume
GT4FS pack --read <path to extracted volume with edited contents> --output MyNewVolume.VOL

Once you're done, you can build your iso file (refer to the ISO building guide).