Why is my iPhone always on E?

I have a jail broke iPhone 4S which one day I rebooted and it always says E instead of 4G how do I fix it

You can't, you jailbroke it, now live with the consequences. What is really the point of doing this?

I'd like to inform you that your phone is not broken. I will happily give you some information about possible ways to fix your iPhone's problem.

About E:
• E, like 3G, 4G, and 4G LTE, is a cellular data network. E, also known as the EDGE network, is the 1st Generation cellular data network. It's slow, and it's not even really useful on the iPhone.

Solution 1:
Try this solution first.
1. Go to Settings.
2.In Settings go to General.
3.In General go to Cellular.
• It should show cellular data as being on when you arrive to the page.
4. Turn Cellular Data OFF.
5. Restart your iPhone, or re-spring it in your case.
6. Once your iPhone is back on, go back into Settings.
7. Once again, go to General and then to Cellular.
• It should show cellular data as being off when you arrive to the page this time.
8. Turn Cellular Data ON.
• The 4G icon should appear shortly if this worked. If this didn't work go on to the next step (9).
9. Go back to General, then go back to Settings.
10. At the top of everything, you will see something that says Airplane Mode, turn this on.
• Airplane mode will disable Wi-Fi, Cellular Data, and Bluetooth while it's on. Once you turn Airplane Mode back off, you will be able to use everything again. Also, you have the option to turn Wi-Fi on while in Airplane mode.
11. Restart your iPhone.
12. When your iPhone is back on, go back into Settings and turn off Airplane Mode.
• If this solution did not work for you, continue onto the next solution.

Solution 2:
1. Check to see if there's anything you've installed that contains the words E, 3G, 4G, LTE, Wi-Fi, or network.
• If you have anything installed on your iPhone that contains those words in its name or description, it's possible that that's what may be causing your problem.
2. If you're not able to find anything obvious that may have caused this, continue onto the next step.
3. Uninstall all things you've installed onto your phone while it has been jailbroken. Doing so will help you to discover the cause of why you're unable to use the 4G network on your iPhone. (When uninstalling stuff, uninstall the things that are closely related to settings changes).

Solution 3:
1. Check springboard, winterboard, or summerboard (All are pretty much the same thing) for anything containing the word E, 3G, 4G, LTE, Wi-Fi, or Network.
2. If you find something similar to the words above, disable it and Re-Spring your iPhone's SpringBoard.

I hope you are able to resolve this problem, and good luck.