If I put Ex 02 sensors on my Hx will they make the CEL go on?

PS. Is there anything I need to worry about if I buy a brand new 50 dollar header of ebay, or should I just expect minimal hp gains?

Thanks

 

hx is 5wire, ex is 4wire.

hx has 1 5wire and 1 4wire.

depends on which o2 you're trying to replace.

 

to put what Bense said a different way...
since your HX is an OBD2 car is has two O2 sensors.
one before the cat and one after.
the one before the cat is a 5 wire wideband O2 that is not swapable with any other civic other than the VX. (see NGK L1H1 or L2H2)
the O2 after the cat is a standard four wire O2.