Today I changed the plugs and stuff on my 07 gt. Now my check engine light came on could someone tell please please what the problem is

 

Check to make sure you connected everything back in place. If you removed any wire to get it out of the way, maybe you forgot to connect it, or didn't get it seated back in place.

If you don't have a tuner to pull the code you can go to an AutoZone or similar store. They have a code reader and will tell you what the code is. Then you know what the problem is and where to look.

 

"Stuff"... That gives us a lot to go on.

 

I have a similar problem and still have not figured it out. I have an 06 Roush Stage 3 and just replaced the plugs, about 50 miles later the check engine light came on. The code indicated an ignition problem with #3, since I wanted to upgrade my coils anyway I installed Accel super coils. About 30 miles later the light came back on, this time it indicates an ignition problem with #1,2,3 and 4. I've cleared the problem three times and it comes back after about 30-40 miles, but the car runs great ..... Starts right up, idles fine, has good acceleration. I can't figure it out.

 

What plugs did you and the OP use?

I hate Accel coils, they suck. If your car starts to run like ****, you not need look any farther than the Accel coils.

 

Most aftermarket COPs for us are not reliable. What was your process for install. Did you feel the boot slip over the plug? Are you using the right heat range plug for your Stage III? What are your symptoms? Misfire, popping, lack of power?

 

Yep, if the check engine light wasn't on before, obviously you have to look at the plugs or look for something that was disturbed during the process of replacing the plugs.

IMO those Accel coils are a complete waste of money.

I'd stick with OE plugs and coils unless my car was supercharged. Anything else is just going to create problems.