Navigate inside the Pwnage Tool Bundle for iPhone 4 and locate “iPhone3,1_4.3_8F190.bundle". Copy this package to the FirmwareBundles folder (the folder you located above).
Step 3: This step involves installing RamDisk, which will be used for creating a custom Ramdisk for iPhone 4. Perform this step carefully. Double Click the Universal Ramdisk fixer package to install it. Continue to press the “Continue" button, until you see a message that says, “The Installation was successful".
Step 4: Launch Pwnage Tool 4.2 and click Expert mode on the top. Now, select your iPhone 4 device from the application screen. The left iPhone on the app screen is the correct device. If you are not taken to the next screen, click the right arrow located on the bottom right corner of Pwnage Tool 4.2 application screen.
Now, click on “Browser for ipsw" icon and select the iOS 4.3 ipsw file that you downloaded earlier. If you are not taken to the next screen, click the right arrow located on the bottom right corner of Pwnage Tool 4.2 application screen.
Click on “Build" icon so that Pwnage Tool can create a custom jailbroken iOS 4.3 ipsw file, which will be used to jailbreak your iPhone 4.
Exit the Pwnage Tool 4.2 application when done.
NOTE: Create a copy of the iOS 4.3 custom firmware file and place it in the same folder where you have placed all the other downloaded files. Rename this file to .zip and extract it in the same folder.
Step 5: Next step involves restoring your iPhone with the custom jailbroken iOS 4.3 Firmware created in the previous step. Connect your iPhone to the computer and run iTunes. When iTunes detects your iPhone, if you are asked to update your iPhone to the new firmware, DO NOT upgrade it.
Instead, press the Left Alt key and click “Restore" button in iTunes. This will bring a popup window, asking you to select the firmware file. Now, select the custom iOS 4.3 ipsw file you created above.