Issue's after installing DT headers

[Neogixxer]

I installed some long tube Doug thorley headers today with the CEL eliminators.
O2 sensors are in the right spot.
Got new manifold gaskets
New crush gaskets from the 2nd cat to the DT header

Now it feels like it has a loss of power and slightly hesitates (Boggs)upon acceleration (only from a complete stop) although the the MPG seems better.

Things I'm thinking is the problem:
The rest of the exhaust is stock, muffler seems shot tho (muffler replacement)
I crushed the gasket bolting the DT to the 2nd cat but had to remove it an re bolt it, possible air leak.
I didn't reset the ECU, although the CEL isn't on.

Does anyone with passed experiences in header installs on 1st gen xterra's come across similar issues and have any solutions?

Thanks everyone for your help.

 

[Prime]

Are you still running the factory mid pipes? If so, how many miles?

 

[Neogixxer]

Yes, truck has 167,000 miles

 

[Prime]

Sounds like your secondary cats are clogged. Problem is, there aren't readily available replacements that are any good. Since removing the primary cats with the headers, you'll burn out any of the OE cats you put behind them. So your best bet is to hit an exhaust shop and have them make you some mid-pipes with hi-temp cats in them. You have to have some cats for Federal law, and being in Vegas, you've gotta pass a sniffer. So if you get a pair of hi-temp, hi flow cats, you can have your cake and eat it too.

 

[Neogixxer]

Wouldn't that trigger my CEL? Or it probably isn't because of the CEL eliminator?

 

[Muadeeb]

The O2 sensors work by having one in the manifold, before any cats to see how the exhaust looks, then one after the cats to verify how well the exhaust is getting cleaned up which will cause the engine to adjust the fuel/air ratio. Using a CEL Eliminator causes the rear sensor to read less exhaust gas, thereby tricking the engine into thinking the front cat (which doesn't exist) is working properly. The rear cat is never monitored.

As Prime said, have a shop put in a custom pipe with a cat between the header and the Y pipe so you can pass emissions. Or go whole hog and do a fully custom exhaust.