As you can see in my signature, I have long tubes and a catted X-pipe on my car. It has been throwing a check engine light with the code P0430. I don't notice any drivability issues, rough idling, or anything like that, so I turned my rear O2 sensors off last night.

After passing a little Saturn ricer this morning, I realized that my speedometer was off. I think when I turned my sensors off, it reset my computer and erased my tune for the 4.10's. Now I am about 10-15mph off.

Did I do something wrong? Do they cancel each other out? Can I even have both tunes on my car, or can I only have one at a time?

Sorry for all the questions, guys. I just don't understand this tuning stuff.

 

That shouldn't have happened, unless you put in a completely new tune instead of the slight modification for the rear O2s.

 

I very well could have. I will try it again when I get home and see what happens. Thank you.