Had them installed last Friday, everything seemed to be good.

Now I've noticed every time I start the car, the 1st and 2nd gear have no power and I can hear the headers/exhaust make this farting noise.

After I give it more power and switch to 3rd this problem goes away until I start the car again and go into 1st and 2nd.

Anyone know what might be wrong?

 

Wow, hmmmm. There really isnt much wrong you can do when installing headers unless you ruined your O2 sensor.

When you took it out of your old pipe, did you make sure to secure it during your install?

Not much else I can think of besides the O2.

 

I had to replace the old o2 sensor with a universal one.

Could that have been it? It secured in the bung and no codes.

 

Sometimes your O2 sensor won't throw a code even if it is acting haywire. Honestly, I would just disconnect your battery for 10 minutes and reset everything and see what happens.

 

agree

 

Check to make sure you don't have an exhaust leak. When the exhaust sounds like a fart it generally means you have an exhaust leak. I would wait until the car is cold to check for the leaks so you don't burn yourself.

 

yea the farting or a hissing noise could be a leak. With a leak, you will have no backpressure and no torque. It would make the bottom end feel weak and you will have to rev it up high to get power.

 

Just go around and torque all the bolts back up. They tend to loosen up a little after the headers have been installed for a little while.

 

yea something is not right here.

 

try the battery disconnect thing, but leave it disconnected for over 3 hours.
Then wait one day of driving to see a difference. The car will feel funny when you first plug her back in but as it goes back to normal, you will know if the problem is fixed. If that fails, then do what excellerate said, exhasut leaks will do that.

 

Unplugged the battery and plugged it back in after one hour the other day, still getting the same problem.

I'm going back to the mechanic to check for exhaust leak.

Its every time I start the car and give it gas on the first & second gears this happens.