SO i just completed my B18a1 swap into my '90 DX. The car idles well, But when you drive the car feels like it have a lack of power and it hesitates. The thing i am most worried about is that the header all the way back to the cat smokes as if oil is on it. At first i thought it was just stuff burning off but it keeps doing it. I have a new o2 sensor and its in the correct spot.

 

what ecu are you using?

seems to me you're either running lean and extra hot because of it, or you might have a plugged up cat.

 

or your timing is off

 

Wiring or timing; I'd start there. It being the DX, I'd start with looking at the wiring.

 

It almost sounds as if your cat is bad. It could be restrictive. Possibly plugged. Once you've checked what ECU you're running I would take that cat down and inspect it.

 

i didnt think of this earlier, but it could be that the donut gaskets on the manifold are bad, and you're seeing seeping exhaust.