So i dumped my exhaust right before the rear axle on my 2010 5.4 with custom tunes from MPT but ever since i took off my cat back banks monster system and dumped the exhaust i can tell i lost some power and about 2-3 miles per gallon. Is this because i havent updated my tunes yet for the new lower amount of back pressure?

 

Did you disconnect the sensors that went into the Cat Converter?
If so you are almost certainly running lean, which is NOT good for your motor. Get a custom tune or go back to stock asap...

 

No i didnt but i did disconnect the negative battery terminal to reset the ecu. So should i return to stock tune reset ecu and unplug then plug back in the sensor in the cat converter and then get my tunes updated for the dump?

 

I didnt think it would mess with much since i didnt touch the cats hopefully i can get this solved soon

 

Ive already switched back to the stock tune so now do i unplug the negative terminal of the battery to reset the ecu or do i have to unplug and plug back in the sensor on the cat converter or both?

 

Is it fine since i didnt disconnect them?

 

If your retuning you truck with a programmer you don't need to disconnect the battery since when you tune back to stock it starts the ecu back at "zero".
Sorry, I miss read your post. I think the MPT tune might be making your truck run lean due to the drop in back pressure. Try running a few weeks with no tune and see if your problem with the MPGs is fixed. Call MPT and see if they have any custom tunes for the 5.4L with low back pressure, they will try to help you out.

 

Call MPT, they made your last custom tune, they can tell you if the exhaust you have now is compatible with the tune or if you'll need to change it.